Adding fractions with unlike denominators introduction

WEBVTT
Kind: captions
Language: en

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- [Instructor] In this video
we're gonna try to figure out

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what 1/2 plus 1/3 is equal to.

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And like always, I encourage
you to pause this video

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and try to figure it out on your own.

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All right, now let's work
through this together.

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And it might be helpful
to visualize 1/2 and 1/3.

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So this is a visualization of 1/2

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if you viewed this entire bar as whole,

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then we have shaded in half of it.

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And if you wanted to visualize
1/3 it looks like that.

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So you could view this as this half

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plus this gray third here,

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what is that going to be equal to?

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Now one of the difficult
things is we know how to add

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if we have the same denominator.

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So if we had a certain
number of halves here

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and a certain number of halves here,

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well then we would know how
many halves we have here.

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But here we're trying
to add halves to thirds.

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So how do we do that?

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Well we try to set up
a common denominator.

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Now, what do we mean by
a common denominator?

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Well what if we could
express this quantity

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and this quantity in terms
of some other denominator.

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And a good way to think about it is

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is there a multiple of two and three

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and it's simplest when you
use the least common multiple

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and the least common multiple
of two and three is six.

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So can we express 1/2 in terms of sixths

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and can we express 1/3 in terms of sixths?

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So we can just start with one over two

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and I made this little fraction
bar a little bit longer

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'cause you'll see why in a second.

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Well if I wanna express
it in terms of sixths,

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to go from halves to sixths,

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I would have to multiply
the denominator by three.

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But if I want to multiply
the denominator by three

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and not change the value of the fraction,

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I have to multiply the
numerator by three as well.

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And to see why that makes
sense, think about this.

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So this, what we have in green,

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is exactly what we had before but now

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if I multiply it the numerator
and the denominator by three,

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I've expressed it into sixths.

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So notice, I have six
times as many divisions

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of the whole bar.

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And the green part which you
could view as the numerator,

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I now have three times as many.

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So these are now sixths.

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So I now have 3/6 instead of 1/2.

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So this is the same
thing as three over six

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and I want to add that or if
I want to add this to what?

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Well how do I express
1/3 in terms of sixths?

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Well the way that I could do
that, it's one over three,

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I would want to take each of these thirds

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and make them into two sections.

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So to go from thirds to sixths
I'd multiply the denominator

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by two but I'd also be
multiplying the numerator by two.

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And to see why that makes sense,

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notice this shaded in gray part is exactly

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what we have here but now we
took each of these sections

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and we made them into two sections.

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So you multiply the numerator
and the denominator by two.

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Instead of thirds, instead
of three equal sections,

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we now have six equal sections.

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That's what the denominator times two did.

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Instead of shading in just one of them,

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I now have shaded in two of them

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because that one thing that I shaded

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has now turned into two sections.

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And that's what multiplying
the numerator by two does.

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And so this is the same thing as 3/6

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plus this is going to be 2/6.

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And you can see it here.

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This is 1/6, 2/6, and now
that everything is in terms

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of sixths, what is it going to be?

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Well it's going to be a
certain number of sixths.

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If I have three of something
plus two of that something,

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well it's going to be
five of that something.

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In this case, the something is sixths.

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So it's going to be 5/6.

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I have trouble saying that.

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And you can visualize it right over here.

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This is three of the
sixths, one, two, three,

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plus two of the sixths,
one, two, gets us to 5/6.

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But you could also view
it as this green part

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was the original half and this gray part

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was the original 1/3, but
to be able to compute it,

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we expressed both of
them in terms of sixths.


Fraction multiplication as scaling examples

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Kind: captions
Language: en

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- [Instructor] This right over here

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is an image from an exercise
on Khan Academy and it says

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compare using greater than,
less than, or equal to.

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And on the left, we have 1/4 times 5,000,

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and we wanna compare that to 5,000.

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On Khan Academy, you would
click on this drop-down

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and you would pick greater
than, less than, or equal to.

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So what do you think it is?

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How does 1/4 times 5,000 compare to 5,000?

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And how do you know
your answer is correct?

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Pick one of these choices as well.

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Pause the video and have a go at that.

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Well, one way to think about it,

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if I'm multiplying 5,000 times some value,

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that value is going to scale 5,000.

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It's going to make it smaller or bigger

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or in certain cases, might
not change the size at all.

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In fact, the ones where
you don't change 5,000

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was you multiply it by one.

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So one times 5,000 is equal to 5,000.

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But what do you think is going to happen

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when you multiply a value

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that is between zero and one times 5,000?

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Is that going to be
greater than, equal to,

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or less than 5,000?

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Well one way to imagine
it is on a number line.

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If this is zero, this is 5,000.

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This would be halfway
between zero and 5,000.

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And if I then make it the
space between zero and 5,000

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into fourths, this would be 1/4 of the way

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between zero and 5,000.

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So this value right over here,

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that is 1/4 times 5,000.

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Well, how does this value,

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1/4 times 5,000, compare
to this value, to 5,000?

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Well, it's clear that 1/4 times 5,000

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is less than,

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is less than 5,000.

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And in general, if the value
is between zero and one

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that you're multiplying by something else,

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it's going to make the thing
you're multiplying smaller.

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If this were one, it's not
going to change the value.

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And if this were greater than one,

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it would make it larger.

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So let's see these choices.

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Because we are multiplying
5,000 by a fraction

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that is less than one.

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Yeah, that's exactly what's happening.

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We're multiplying 5,000 by 1/4.

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So it's going to give us a
smaller value than 5,000.

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I like that choice.

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Let's just read these other ones.

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Because we are multiplying
5,000 by a fraction

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that is equal to one.

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Well no, 1/4 is clearly not equal to one,

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so we rule that one out.

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Because we are multiplying
5,000 by a fraction

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that is greater than one.

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Well 1/4 is clearly not greater than one,

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so we rule that out as well.

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Let's do another example.

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So here we're asked,

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is the product of each
expression less than,

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equal to, or greater than 49?

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So pause this video and
try to figure it out.

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All right, so this first
one is 49 times 7/8.

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So what do you think that's going to be?

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Well, 7/8 is less than one.

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So if I multiply 49 times
something less than one,

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I'm going to get a value
that is less than 49.

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So I like that choice right over there.

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49 times 5/2.

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Well, 5/2 is greater than one.

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Remember, 2/2 would be equal to one.

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So 5/2 is greater than one.

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So if I'm multiplying 49 by a value

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that is greater than one,
I'm going to get a value

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that is greater than 49.

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And then last but not least, 49 times 3/3.

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Well, 3/3 is exactly equal to one.

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So 49 times one is going
to be exactly equal to 49,

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and we're done.


Estimating adding fractions with unlike denominators

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Kind: captions
Language: en

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- [Instructor] We are told
that Tony has 2/3 of a bag

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of dark chocolate chips

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and 4/5 of a bag of white chocolate chips.

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Determine a reasonable estimate

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of the total amount of
chocolate chips Tony has.

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So pause this video

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and see if you can figure
out which of these choices

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is the best reasonable estimate

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of the total amount of chocolate chips.

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All right, now let's
work on this together.

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Now in the future,

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we will learn how to actually
add something like 2/3

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to 4/5, but for the sake of this exercise,

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we just want to get good at estimating it.

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And one way to estimate
is to try to visualize.

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So let's make,

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so this is a whole right over here,

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and then this is another
whole right over there.

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Try to make them the same size.

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Now what does 2/3 look like?

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Well, let me divide this
into three equal sections,

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so that is pretty close.

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It's hand drawn, so it's not perfect,

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but I think it gets the job done.

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And 2/3 would be, that's
1/3 right over there

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and then that is 2/3 right there,

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and what does 4/5 looks like?

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Well, let's see.

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I can divide this into fifths,

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so 1/5, 2/5,

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3/5, and then 4/5, and 5/5.

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That is pretty good.

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And now what does 4/5 look like?

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Well, it would be 1/5,

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2/5, 3/5, and then 4/5.

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So if we were to add these two together,

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do we have less than 1/2 of a bag,

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more than 1/2 of a bag,
but less than one bag,

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or more than one bag?

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Well, when you see even the first 2/3,

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where is a half?

00:01:49.290 --> 00:01:52.800
A half would have been right around there

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if we're talking about half of it.

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So 2/3 is more than a half,

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and then we also see that
4/5 is more than a half.

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If you had a half,

00:02:02.660 --> 00:02:05.470
it would have been like this far.

00:02:05.470 --> 00:02:08.280
So you can see that you're
adding two things together

00:02:08.280 --> 00:02:10.140
that are both more than a half.

00:02:10.140 --> 00:02:13.350
And if you have two halves of
something, that'd be a whole,

00:02:13.350 --> 00:02:15.140
so if you have two things
that are more than a half,

00:02:15.140 --> 00:02:16.080
if you add them together,

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you're gonna have more than
a bag of chocolate chips.

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So I like this choice right over here.

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Let's do another example.

00:02:24.450 --> 00:02:27.220
So here, we are told

00:02:27.220 --> 00:02:30.700
that a banana weights 3/8 of a kilogram,

00:02:30.700 --> 00:02:33.300
an apple weighs 2/3 of a kilogram.

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Determine a reasonable estimate

00:02:34.960 --> 00:02:36.750
for the weight of both fruits.

00:02:36.750 --> 00:02:37.820
So pause this video again

00:02:37.820 --> 00:02:40.170
and see if you can have a go at that.

00:02:40.170 --> 00:02:41.730
All right, so the key is that we need

00:02:41.730 --> 00:02:44.420
to determine a reasonable estimate.

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So let's actually just try
to represent these again,

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so how could I represent 3/8 of something,

00:02:49.450 --> 00:02:51.310
of a kilogram, in this case?

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Well, let me draw a rectangle here

00:02:53.660 --> 00:02:56.320
and I'm going to try to
divide it into eighths,

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eight equal sections,

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so that looks about a half.

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Let me do it right over there.

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That looks like about a half,

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and then if I were to divide those,

00:03:06.910 --> 00:03:08.450
these would be fourths,

00:03:08.450 --> 00:03:10.950
and this is hand drawn,
so it's not perfect,

00:03:10.950 --> 00:03:14.110
but it will help us
understand things a bit.

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So then let me divide these,

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and so this would get me to eighths.

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So I have eight sections here.

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One, two, three, four,
five, six, seven, eight,

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and if I'm talking about three

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of those eight equal sections,

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I'd have 1/8, 2/8, and 3/8,

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so that is 3/8 right over there

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and what does 2/3 looks like?

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So I'll do that in purple,

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so if this is a whole,

00:03:40.260 --> 00:03:42.580
this is a whole like that.

00:03:42.580 --> 00:03:44.600
If I divide it into three equal sections,

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it's going to be something like that.

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I could draw it a little bit better,

00:03:49.640 --> 00:03:51.950
so something like that,

00:03:51.950 --> 00:03:53.790
and so two of those three equal sections,

00:03:53.790 --> 00:03:58.200
that's 1/3, and so that is 2/3.

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Now what happens if I try to
add these things together?

00:04:01.050 --> 00:04:04.160
Well one thing I could try
to do to help visualize

00:04:04.160 --> 00:04:05.810
is I could take that piece there.

00:04:05.810 --> 00:04:07.860
The wholes are roughly the same length

00:04:07.860 --> 00:04:09.534
or I tried to draw them

00:04:09.534 --> 00:04:10.640
so that they are roughly the same length,

00:04:10.640 --> 00:04:12.600
and if I were to copy and paste that

00:04:12.600 --> 00:04:15.360
and move that over here,

00:04:15.360 --> 00:04:17.790
it looks like, if I were to estimate it,

00:04:17.790 --> 00:04:20.580
I'm getting pretty close
to a whole kilogram here.

00:04:20.580 --> 00:04:24.930
So it's definitely not just
about 1/3 of a kilogram.

00:04:24.930 --> 00:04:28.590
1/3 of a kilogram would be just one

00:04:28.590 --> 00:04:29.800
of these three equal sections.

00:04:29.800 --> 00:04:32.420
We're way more than that,
so we rule that out.

00:04:32.420 --> 00:04:34.430
About one kilogram, that's what we saw.

00:04:34.430 --> 00:04:35.310
When we,

00:04:35.310 --> 00:04:39.950
when we take the 2/3 and add to that, 3/8,

00:04:39.950 --> 00:04:43.010
where it looks like, and
once again, we're estimating.

00:04:43.010 --> 00:04:44.190
We don't know exactly.

00:04:44.190 --> 00:04:46.270
It looks like we're a
little bit over a kilogram,

00:04:46.270 --> 00:04:47.520
so I like this choice,

00:04:47.520 --> 00:04:49.510
and we're no where close to two kilograms.

00:04:49.510 --> 00:04:51.990
Two kilograms, we would be
filling in another whole

00:04:51.990 --> 00:04:53.960
on top of this one right over here.

00:04:53.960 --> 00:04:55.853
So it's not that choice either.


Periodic trends and Coulomb's law

WEBVTT
Kind: captions
Language: en

00:00:00.350 --> 00:00:01.980
- [Instructor] In this video
we're going to look at trends

00:00:01.980 --> 00:00:03.740
for the periodic table of elements

00:00:03.740 --> 00:00:06.040
for dimensions like ionization energy,

00:00:06.040 --> 00:00:09.210
atomic and ionic radii, electron affinity,

00:00:09.210 --> 00:00:11.030
and electro negativity.

00:00:11.030 --> 00:00:13.840
And to do so, we're going to start with

00:00:13.840 --> 00:00:17.290
a very fundamental idea
in chemistry or physics,

00:00:17.290 --> 00:00:18.910
and that's Coulomb's Law.

00:00:18.910 --> 00:00:22.110
And for our point of view,
we can view Coulomb's Law

00:00:22.110 --> 00:00:24.340
as saying that the magnitude of the force

00:00:24.340 --> 00:00:27.390
between two charged
particles is going to be

00:00:27.390 --> 00:00:30.040
proportional, that just means
proportional right there,

00:00:30.040 --> 00:00:32.580
is going to be proportional to the charge

00:00:32.580 --> 00:00:34.620
on the first particle times the charge

00:00:34.620 --> 00:00:37.410
on the second particle,
divided by the distance

00:00:37.410 --> 00:00:40.720
between those two particles, squared.

00:00:40.720 --> 00:00:42.030
When we're thinking about it in context

00:00:42.030 --> 00:00:45.210
of the periodic table of
elements and various atoms,

00:00:45.210 --> 00:00:48.600
you can view q1 as the
effective positive charge

00:00:48.600 --> 00:00:51.930
from the protons in
the nucleus of an atom.

00:00:51.930 --> 00:00:55.060
You can view q2 as the
charge of an electron.

00:00:55.060 --> 00:00:57.980
Now any given electron is going to have

00:00:57.980 --> 00:01:01.230
the same negative charge,
but as we try to understand

00:01:01.230 --> 00:01:02.810
trends in the period table of elements,

00:01:02.810 --> 00:01:05.120
it's really the outer
most shell electrons,

00:01:05.120 --> 00:01:07.880
the valence electrons,
that are most interesting.

00:01:07.880 --> 00:01:10.120
Those are the ones that
describe the reactivity.

00:01:10.120 --> 00:01:12.270
And so when we think about the distance

00:01:12.270 --> 00:01:15.270
between the two charges
we're mainly going to be

00:01:15.270 --> 00:01:17.830
thinking about the distance
between the nucleus

00:01:17.830 --> 00:01:21.330
and those outer most valence electrons.

00:01:21.330 --> 00:01:24.790
Now we can view this effective charge,

00:01:24.790 --> 00:01:29.100
I'll call it z-effective, as
being equal to the difference

00:01:29.100 --> 00:01:31.020
between the charge in the nucleus,

00:01:31.020 --> 00:01:34.040
so you can just view this
as the atomic number,

00:01:34.040 --> 00:01:36.440
atomic number or the number of protons

00:01:36.440 --> 00:01:40.280
that a given element or an
atom of that element has,

00:01:40.280 --> 00:01:44.230
and the difference between
that and what is often known as

00:01:44.230 --> 00:01:46.740
S, or how much shielding there is.

00:01:46.740 --> 00:01:48.650
Now there is complicated models for that,

00:01:48.650 --> 00:01:50.700
but for an introductory chemistry class,

00:01:50.700 --> 00:01:55.700
this is often approximated by
the number of core electrons.

00:01:57.850 --> 00:01:59.770
Remember, we really want to think about

00:01:59.770 --> 00:02:02.580
what's going on with
the valence electrons.

00:02:02.580 --> 00:02:06.140
And so if you imagine a nucleus here,

00:02:06.140 --> 00:02:08.600
do that orange color,
that has protons in it.

00:02:08.600 --> 00:02:10.960
And so you have core electrons.

00:02:10.960 --> 00:02:14.730
Let's say these are the core
electrons in the first shell,

00:02:14.730 --> 00:02:18.480
and then you have some core
electrons in the second shell.

00:02:18.480 --> 00:02:21.750
And let's say the valence
electrons are in the third shell.

00:02:21.750 --> 00:02:23.510
So let's say these are some
valence electrons here,

00:02:23.510 --> 00:02:25.590
they're blurred around,
they're in these orbitals.

00:02:25.590 --> 00:02:28.330
Those valence electrons,
which have a negative charge,

00:02:28.330 --> 00:02:30.230
are going to be attracted
to the positive charge

00:02:30.230 --> 00:02:32.370
of the nucleus but
they're also going to be

00:02:32.370 --> 00:02:34.450
repulsed by all these core electrons

00:02:34.450 --> 00:02:35.570
that are in between them.

00:02:35.570 --> 00:02:38.070
And so that's why an approximation

00:02:38.070 --> 00:02:41.030
of the effective charge
that these valence electrons

00:02:41.030 --> 00:02:43.190
might experience is going to be the charge

00:02:43.190 --> 00:02:46.930
of the nucleus minus, and
this is an approximation,

00:02:46.930 --> 00:02:49.930
the number of core
electrons that you have.

00:02:49.930 --> 00:02:52.020
So if we use that roughly
as a way to think about

00:02:52.020 --> 00:02:54.650
z-effective, what do you
think are going to be

00:02:54.650 --> 00:02:56.963
the trends in the periodic
table of elements?

00:02:58.460 --> 00:02:59.860
What would be the effective charge

00:02:59.860 --> 00:03:02.610
for the Group I elements over here?

00:03:02.610 --> 00:03:05.200
Well, Hydrogen has no core electrons

00:03:05.200 --> 00:03:06.930
and it has an atomic number of 1.

00:03:06.930 --> 00:03:08.620
So 1 minus 0 is going to have

00:03:08.620 --> 00:03:10.690
an effective charge of roughly 1.

00:03:10.690 --> 00:03:15.480
Lithium atomic number of
3, minus 2 core electrons

00:03:15.480 --> 00:03:18.750
that are in 1-S, so once
again you're going to have

00:03:18.750 --> 00:03:21.830
3 minus 2, effective charge of 1.

00:03:21.830 --> 00:03:23.790
So roughly speaking, all of these Group I

00:03:23.790 --> 00:03:25.920
elements have an effective charge of 1.

00:03:25.920 --> 00:03:26.897
What if you were to go to the halogens?

00:03:26.897 --> 00:03:29.630
What's the effective charge there?

00:03:29.630 --> 00:03:32.680
Well if you look at
Flourine, atomic number of 9,

00:03:32.680 --> 00:03:35.600
has 2 core electrons in the first shell,

00:03:35.600 --> 00:03:38.440
so has an effective charge of 7.

00:03:38.440 --> 00:03:40.570
Chlorine actually has
an effective charge of 7

00:03:40.570 --> 00:03:42.000
for the same reason.

00:03:42.000 --> 00:03:45.880
Atomic number of 17,
but 10 core electrons.

00:03:45.880 --> 00:03:47.590
If you go even further to the right,

00:03:47.590 --> 00:03:50.550
to the noble gases, you see that Helium

00:03:50.550 --> 00:03:54.140
is going to have an effective charge of 2,

00:03:54.140 --> 00:03:57.160
atomic number of 2 minus 0 core electrons.

00:03:57.160 --> 00:03:58.780
But then when you get to Neon,

00:03:58.780 --> 00:04:00.860
you have an atomic number of 10,

00:04:00.860 --> 00:04:03.960
and then minus only 2 core electrons.

00:04:03.960 --> 00:04:06.670
And you'll see as you go
down these noble gases,

00:04:06.670 --> 00:04:10.000
other than Helium, they have
an effective charge of 8.

00:04:10.000 --> 00:04:13.265
And so the general trend is,
your effective charge is low

00:04:13.265 --> 00:04:17.530
at the left, effective
charge low for Group I,

00:04:17.530 --> 00:04:19.590
and then when you go to the
right of the periodic table,

00:04:19.590 --> 00:04:24.590
you have a z-effective,
is going to be high.

00:04:25.520 --> 00:04:28.090
So within a given period,
or within a given row

00:04:28.090 --> 00:04:30.200
in the periodic table of elements,

00:04:30.200 --> 00:04:32.390
your outer electrons,
your valence electrons,

00:04:32.390 --> 00:04:34.240
are in the same shell.

00:04:34.240 --> 00:04:36.270
But the effective charge is increasing

00:04:36.270 --> 00:04:37.720
as you go from left to right.

00:04:37.720 --> 00:04:40.980
So this q1 right over here
is going to be increasing.

00:04:40.980 --> 00:04:43.560
So what is that going to do
to the radius of the atom?

00:04:43.560 --> 00:04:45.750
Well, Coulomb's Law will
say that the magnitude

00:04:45.750 --> 00:04:48.770
of the attractive force
between those opposite charges

00:04:48.770 --> 00:04:50.490
is going to be stronger.

00:04:50.490 --> 00:04:53.240
And so even though you're adding electrons

00:04:53.240 --> 00:04:55.630
as you go from left to right within a row,

00:04:55.630 --> 00:04:58.340
within a period, the atoms in general

00:04:58.340 --> 00:05:00.410
are actually going to get smaller.

00:05:00.410 --> 00:05:01.410
Let me write it this way.

00:05:01.410 --> 00:05:04.140
So as you go from left to
right, generally speaking,

00:05:04.140 --> 00:05:06.570
radius decreases.

00:05:06.570 --> 00:05:09.040
Now what's the trend within a column?

00:05:09.040 --> 00:05:11.130
Well one way to think about it is,

00:05:11.130 --> 00:05:14.510
as you go down a column,
as you go down a Group,

00:05:14.510 --> 00:05:17.420
you're filling shells
that are further out.

00:05:17.420 --> 00:05:19.760
And so you'd expect radius to increase

00:05:19.760 --> 00:05:22.600
as you go down a column, or down a Group.

00:05:22.600 --> 00:05:25.950
Or you could say radius
decreases as you go up a group.

00:05:25.950 --> 00:05:28.560
So radius decreases.

00:05:28.560 --> 00:05:30.160
So overall what's the trend

00:05:30.160 --> 00:05:32.240
in the periodic table of elements?

00:05:32.240 --> 00:05:34.650
Well radius is going to decrease as you go

00:05:34.650 --> 00:05:36.200
up and to the right.

00:05:36.200 --> 00:05:40.400
And so you could draw an
arrow something like this.

00:05:40.400 --> 00:05:43.260
And it is indeed the case
that by most measures,

00:05:43.260 --> 00:05:46.260
Helium is considered to
be the smallest atom,

00:05:46.260 --> 00:05:47.610
a neutral Helium atom.

00:05:47.610 --> 00:05:51.985
And Francium is considered
to be the largest atom.

00:05:51.985 --> 00:05:54.120
So could we use this to think about

00:05:54.120 --> 00:05:56.410
other trends in the
periodic table of elements?

00:05:56.410 --> 00:05:59.453
What about, for example,
ionization energy?

00:06:00.290 --> 00:06:03.090
Just as a reminder, the
first ionization energy

00:06:03.090 --> 00:06:05.540
is the minimum energy required

00:06:05.540 --> 00:06:09.000
to remove that first electron

00:06:09.000 --> 00:06:12.300
from a neutral version of that element.

00:06:12.300 --> 00:06:13.680
And since it's the minimum energy,

00:06:13.680 --> 00:06:15.490
it's going to be one of
those outer most electrons.

00:06:15.490 --> 00:06:18.560
It's going to be one of
the valence electrons.

00:06:18.560 --> 00:06:20.610
And so what's going to drive that?

00:06:20.610 --> 00:06:22.920
Well you can imagine the ionization energy

00:06:22.920 --> 00:06:25.130
is going to be high in cases where

00:06:25.130 --> 00:06:27.490
the Coulomb forces are high.

00:06:27.490 --> 00:06:29.440
And what are the situations where

00:06:29.440 --> 00:06:31.330
the Coulomb forces are high?

00:06:31.330 --> 00:06:32.690
Well this is going to be a situation

00:06:32.690 --> 00:06:35.370
where you have a high effective charge

00:06:35.370 --> 00:06:38.220
and where you have a low radius.

00:06:38.220 --> 00:06:40.270
Low radius makes the Coulomb forces high.

00:06:40.270 --> 00:06:43.020
And effective charge makes
the Coulomb forces high.

00:06:43.020 --> 00:06:44.780
So where is that true?

00:06:44.780 --> 00:06:49.040
So you have the lowest
radii at the top right

00:06:49.040 --> 00:06:53.510
and you have the highest
effective charge at the right.

00:06:53.510 --> 00:06:56.900
So you would expect the
highest ionization energies

00:06:56.900 --> 00:06:59.620
to occur in the top right.

00:06:59.620 --> 00:07:03.747
So high ionization energy.

00:07:06.300 --> 00:07:08.830
And that actually makes intuitive sense.

00:07:08.830 --> 00:07:11.160
These noble gases are very stable.

00:07:11.160 --> 00:07:12.760
They don't want to release an electron.

00:07:12.760 --> 00:07:14.080
So it's going to take a lot of energy

00:07:14.080 --> 00:07:16.170
to take one of those electrons away.

00:07:16.170 --> 00:07:18.590
Fluorine or Chlorine, they're so close

00:07:18.590 --> 00:07:20.500
to completing a shell, the
last thing they want to do

00:07:20.500 --> 00:07:22.010
is lose an electron.

00:07:22.010 --> 00:07:24.288
So once again, it takes a lot of energy

00:07:24.288 --> 00:07:27.700
to take that first electron away.

00:07:27.700 --> 00:07:29.870
On the other hand, if you go to something

00:07:29.870 --> 00:07:33.490
like Francium, it has
one valence electron.

00:07:33.490 --> 00:07:36.930
And that valence electron is
pretty far from the nucleus.

00:07:36.930 --> 00:07:38.600
And there's a low effective charge

00:07:38.600 --> 00:07:40.760
despite all the protons
because there's so much

00:07:40.760 --> 00:07:42.840
shielding from all those core electrons.

00:07:42.840 --> 00:07:44.740
So it's not surprising
that it doesn't take

00:07:44.740 --> 00:07:46.480
a ton of energy to remove

00:07:46.480 --> 00:07:48.750
that first electron from Francium.

00:07:48.750 --> 00:07:50.650
Now another trend that we can think about,

00:07:50.650 --> 00:07:52.380
which is in some ways the opposite,

00:07:52.380 --> 00:07:55.810
is electron affinity.

00:07:55.810 --> 00:07:58.830
Ionization energy is
talking about the energy

00:07:58.830 --> 00:08:00.850
it takes to remove an electron.

00:08:00.850 --> 00:08:03.640
Electron affinity thinks
about how much energy

00:08:03.640 --> 00:08:06.680
is released if we add an electron

00:08:06.680 --> 00:08:09.910
to a neutral version of a given element.

00:08:09.910 --> 00:08:12.380
So high electron affinity elements,

00:08:12.380 --> 00:08:14.170
these are the ones that
really want electrons.

00:08:14.170 --> 00:08:17.200
So they should have a high Coulomb force

00:08:17.200 --> 00:08:21.780
between their nucleus and
the outer most electrons.

00:08:21.780 --> 00:08:23.470
And so that means they should have

00:08:23.470 --> 00:08:27.530
a high effective z, and that also means

00:08:27.530 --> 00:08:29.810
that they should have a low r.

00:08:29.810 --> 00:08:31.320
So one way to think about
it, you're going to have

00:08:31.320 --> 00:08:34.960
a similar trend with
the one difference that

00:08:34.960 --> 00:08:38.920
the noble gases don't like
gaining or losing electrons.

00:08:38.920 --> 00:08:40.710
But we do know that the
Flourines and the Chlorines

00:08:40.710 --> 00:08:42.470
of the world can be become more stable

00:08:42.470 --> 00:08:43.640
if the gain an electron.

00:08:43.640 --> 00:08:45.650
They can actually release energy.

00:08:45.650 --> 00:08:48.600
So you actually have
high electron affinities

00:08:48.600 --> 00:08:51.400
for the top right,
especially the Halogens.

00:08:51.400 --> 00:08:53.500
And you have low electron affinities

00:08:53.500 --> 00:08:55.720
at the bottom left.

00:08:55.720 --> 00:08:58.440
Now there's one little quirk
in chemistry conventions,

00:08:58.440 --> 00:09:01.170
people will generally say
that Fluorine and Chlorine

00:09:01.170 --> 00:09:03.710
and the things in the top
right that aren't noble gases,

00:09:03.710 --> 00:09:05.490
have a high electron affinity.

00:09:05.490 --> 00:09:07.370
And it is the case that energy is released

00:09:07.370 --> 00:09:10.080
when you add an electron to
a neutral version of them.

00:09:10.080 --> 00:09:11.710
It just happens to be that the convention,

00:09:11.710 --> 00:09:13.090
and this can get a little confusing,

00:09:13.090 --> 00:09:15.100
is that when you release energy you have

00:09:15.100 --> 00:09:17.160
a negative electron affinity.

00:09:17.160 --> 00:09:19.680
But generally speaking, when they say

00:09:19.680 --> 00:09:23.207
a high electron affinity,
this thing's going to release

00:09:23.207 --> 00:09:25.950
more energy when it's
able to grab an electron.

00:09:25.950 --> 00:09:29.530
Now a notion that is
related to electron affinity

00:09:29.530 --> 00:09:31.730
is electro negativity.

00:09:31.730 --> 00:09:33.940
And the difference between
the two can sometimes

00:09:33.940 --> 00:09:36.090
be a little bit confusing.

00:09:36.090 --> 00:09:38.770
Electro negativity is all about when

00:09:38.770 --> 00:09:42.690
an atom shares a pair of
electrons with another atom,

00:09:42.690 --> 00:09:46.560
how likely is it to
attract that pair to itself

00:09:46.560 --> 00:09:48.620
versus for the pair to be attracted away

00:09:48.620 --> 00:09:50.310
from it to the other one?

00:09:50.310 --> 00:09:53.150
And so you can imagine it
correlates very strongly

00:09:53.150 --> 00:09:54.550
with electron affinity.

00:09:54.550 --> 00:09:56.950
Things that release energy
when they're able to be

00:09:56.950 --> 00:10:01.230
ionized to grab an electron,
if they form a bond

00:10:01.230 --> 00:10:03.580
and they're sharing a pair of electrons,

00:10:03.580 --> 00:10:06.780
they are more likely
to hog those electrons.

00:10:06.780 --> 00:10:08.830
Electron affinity is easier to measure.

00:10:08.830 --> 00:10:11.930
You can actually see when this
element's in a gaseous state

00:10:11.930 --> 00:10:14.350
if you add electrons how
much energy is released,

00:10:14.350 --> 00:10:17.020
it's normally measured
in kilojoules per mole

00:10:17.020 --> 00:10:18.950
of the atom in question.

00:10:18.950 --> 00:10:21.730
While electro negativity
isn't as clear cut

00:10:21.730 --> 00:10:24.030
on how to measure it, but
it can be a useful concept

00:10:24.030 --> 00:10:25.833
in future videos as we think about

00:10:25.833 --> 00:10:28.660
different atoms sharing pairs of electrons

00:10:28.660 --> 00:10:31.700
and where do the electrons
spend most of their time.

00:10:31.700 --> 00:10:32.680
So I'll leave you there.

00:10:32.680 --> 00:10:35.220
We started with Coulomb
forces and we were able to

00:10:35.220 --> 00:10:37.823
intuit a whole bunch of
trends just thinking about

00:10:37.823 --> 00:10:42.343
Coulomb's Law and the
periodic table of elements.


Valence electrons and ionic compounds

WEBVTT
Kind: captions
Language: en

00:00:00.660 --> 00:00:01.570
- [Instructor] In this video,

00:00:01.570 --> 00:00:03.160
we're gonna gain even more appreciation

00:00:03.160 --> 00:00:06.310
for why the periodic table
of elements is so useful.

00:00:06.310 --> 00:00:08.490
And in particular, we're going to focus on

00:00:08.490 --> 00:00:11.480
groups of the periodic table of elements.

00:00:11.480 --> 00:00:12.540
When we talk about a group,

00:00:12.540 --> 00:00:14.010
we're just talking about a column.

00:00:14.010 --> 00:00:16.930
And as we'll see, even though
the elements in a given column

00:00:16.930 --> 00:00:19.110
might have very different atomic numbers,

00:00:19.110 --> 00:00:21.350
they all have similar properties.

00:00:21.350 --> 00:00:24.510
And the reason why they all
have similar properties is,

00:00:24.510 --> 00:00:26.830
in most cases, they have the same number

00:00:26.830 --> 00:00:28.030
of valence electrons.

00:00:28.030 --> 00:00:31.750
Remember, valence electrons
are the reactive electrons,

00:00:31.750 --> 00:00:34.060
the ones that might
interact with other things.

00:00:34.060 --> 00:00:36.560
And because elements with
similar valence electrons

00:00:36.560 --> 00:00:40.460
will have similar reactivities,
they will form similar ions.

00:00:40.460 --> 00:00:43.020
Similar ions.

00:00:43.020 --> 00:00:45.080
And they will have similar roles.

00:00:45.080 --> 00:00:50.080
Similar roles in ionic compounds.

00:00:51.190 --> 00:00:53.090
Ionic compounds.

00:00:53.090 --> 00:00:56.060
Now, for the sake of this
video, I'm gonna focus most on

00:00:56.060 --> 00:00:57.830
the extremes of the periodic table,

00:00:57.830 --> 00:01:00.260
the groups at the left and the right,

00:01:00.260 --> 00:01:04.180
because those are the closest
to having a full outer shell,

00:01:04.180 --> 00:01:08.490
either by losing electrons
or by gaining electrons.

00:01:08.490 --> 00:01:09.750
So just to remind ourselves,

00:01:09.750 --> 00:01:14.750
what does it mean to have
a full, full outer shell?

00:01:16.080 --> 00:01:20.400
Well, in general, people
will refer to the octet rule.

00:01:20.400 --> 00:01:24.650
For our second, third, fourth,
fifth, and on and on shells,

00:01:24.650 --> 00:01:26.890
you're full when you have eight electrons.

00:01:26.890 --> 00:01:28.160
Eight electrons.

00:01:28.160 --> 00:01:32.550
The major exception to the
octet rule is the first shell,

00:01:32.550 --> 00:01:35.220
where it is full with two electrons.

00:01:35.220 --> 00:01:37.930
So helium, even though it
only has two electrons,

00:01:37.930 --> 00:01:40.140
is very, very, very stable.

00:01:40.140 --> 00:01:44.000
And the major data point that
we have around this octet rule

00:01:44.000 --> 00:01:46.310
are the group 18 elements right over here,

00:01:46.310 --> 00:01:48.700
also known as the noble gasses.

00:01:48.700 --> 00:01:49.870
They're known as the noble gasses

00:01:49.870 --> 00:01:52.670
because they're very unreactive,
they're very content,

00:01:52.670 --> 00:01:55.070
they don't wanna mess
around with anyone else.

00:01:55.070 --> 00:01:57.280
And that's because all of the noble gasses

00:01:57.280 --> 00:01:59.450
have full outer shells.

00:01:59.450 --> 00:02:02.090
Helium's outer shell is the
first shell and it's full.

00:02:02.090 --> 00:02:04.040
Neon's outer shell's the
second shell, it's full.

00:02:04.040 --> 00:02:06.520
Argon's outer shell is the
third shell and it's full,

00:02:06.520 --> 00:02:08.820
and so on and so forth.

00:02:08.820 --> 00:02:12.240
Now, if we go one group to
the left of the noble gasses,

00:02:12.240 --> 00:02:14.800
we get to the halogens.

00:02:14.800 --> 00:02:18.330
Now, the halogens have
seven valence electrons.

00:02:18.330 --> 00:02:21.970
So you can imagine, they're
only one electron away from

00:02:21.970 --> 00:02:25.030
having an electron
configuration like the noble gas

00:02:25.030 --> 00:02:26.700
to the right of each of them.

00:02:26.700 --> 00:02:28.730
So these halogens right over here,

00:02:28.730 --> 00:02:32.120
these really like to attract electrons

00:02:32.120 --> 00:02:34.740
to form a negative ion or an anion.

00:02:34.740 --> 00:02:39.740
So you'll oftentimes see
fluorine as a fluoride anion,

00:02:41.040 --> 00:02:43.140
so it has a negative one charge.

00:02:43.140 --> 00:02:46.330
Or you'll also see chlorine
with a negative one charge

00:02:46.330 --> 00:02:48.670
as the chloride anion.

00:02:48.670 --> 00:02:49.590
And I could go on and on.

00:02:49.590 --> 00:02:51.870
You'll often see iodine gain an electron

00:02:51.870 --> 00:02:54.610
and have a negative one charge.

00:02:54.610 --> 00:02:58.120
If you go one step to the
left, the oxygen group,

00:02:58.120 --> 00:03:00.830
oxygen, sulfur, and on and on,

00:03:00.830 --> 00:03:03.840
these elements have six valence electrons.

00:03:03.840 --> 00:03:06.650
So it's still easier for them
to have a full outer shell

00:03:06.650 --> 00:03:10.580
by gaining two electrons
than by losing six electrons.

00:03:10.580 --> 00:03:13.990
So these elements also
like to attract electrons.

00:03:13.990 --> 00:03:17.743
So you can see oxygen as an oxide anion.

00:03:17.743 --> 00:03:19.090
It has gained two electrons,

00:03:19.090 --> 00:03:21.020
it's swiped it from somebody else.

00:03:21.020 --> 00:03:24.330
Sulfur as a sulfide anion.

00:03:24.330 --> 00:03:27.640
Now, if you go to the other
extreme of the periodic table,

00:03:27.640 --> 00:03:29.750
if you look at group one elements,

00:03:29.750 --> 00:03:32.270
they have one valence electron.

00:03:32.270 --> 00:03:33.690
And especially the ones that you look,

00:03:33.690 --> 00:03:34.890
and you see in red here,

00:03:34.890 --> 00:03:38.300
which are known as the alkali metals,

00:03:38.300 --> 00:03:41.070
it's much easier for
them to lose an electron

00:03:41.070 --> 00:03:42.640
to have a full outer shell

00:03:42.640 --> 00:03:45.340
than for them to gain seven electrons.

00:03:45.340 --> 00:03:47.210
The reason why hydrogen's
a bit of an exception is

00:03:47.210 --> 00:03:48.780
it doesn't have to gain seven electrons

00:03:48.780 --> 00:03:51.160
to have a full outer
shell, it has to gain one.

00:03:51.160 --> 00:03:52.680
So hydrogen could lose one,

00:03:52.680 --> 00:03:54.700
and essentially have no electrons,

00:03:54.700 --> 00:03:56.860
or it could gain one electron

00:03:56.860 --> 00:04:00.600
and it would have a full
outer shell like helium.

00:04:00.600 --> 00:04:02.780
But when we think about ionic compounds,

00:04:02.780 --> 00:04:04.610
these alkali metals are really

00:04:04.610 --> 00:04:07.200
some of the most interesting participants.

00:04:07.200 --> 00:04:09.920
Because as you can imagine,
for them to get stable,

00:04:09.920 --> 00:04:12.050
they wanna give away an electron.

00:04:12.050 --> 00:04:13.820
So you're very likely to see them

00:04:13.820 --> 00:04:15.440
having given away an electron

00:04:15.440 --> 00:04:17.740
and having a positive one charge.

00:04:17.740 --> 00:04:20.750
So you'll oftentimes see a lithium ion

00:04:20.750 --> 00:04:22.240
with a positive one charge,

00:04:22.240 --> 00:04:24.980
a sodium ion with a positive one charge,

00:04:24.980 --> 00:04:27.310
a potassium ion with
a positive one charge.

00:04:27.310 --> 00:04:28.440
And that's, in general,

00:04:28.440 --> 00:04:30.580
true of all of these group one elements.

00:04:30.580 --> 00:04:32.350
Now, what about these group two elements,

00:04:32.350 --> 00:04:35.040
also known as the alkaline earth metals?

00:04:35.040 --> 00:04:38.170
Well, once again, it's easier
for them to lose two electrons

00:04:38.170 --> 00:04:41.790
than for them to gain six
and have a full outer shell.

00:04:41.790 --> 00:04:44.660
So, you'll typically see beryllium

00:04:44.660 --> 00:04:46.400
having a positive two charge.

00:04:46.400 --> 00:04:48.150
It would have lost those two electrons.

00:04:48.150 --> 00:04:51.100
Magnesium as having a positive two charge.

00:04:51.100 --> 00:04:54.780
Calcium as having a positive two charge.

00:04:54.780 --> 00:04:58.090
Now, given that, how would
you expect things on the left

00:04:58.090 --> 00:05:01.710
and things on the right
to form ionic compounds?

00:05:01.710 --> 00:05:04.300
So you might guess, if
you have an alkali metal

00:05:04.300 --> 00:05:06.920
in the presence of a halogen,

00:05:06.920 --> 00:05:08.770
things could get very reactive.

00:05:08.770 --> 00:05:11.120
In fact, things will get very reactive

00:05:11.120 --> 00:05:13.180
because these wanna give away electron,

00:05:13.180 --> 00:05:14.790
these wanna take electron.

00:05:14.790 --> 00:05:15.930
And that's what will happen.

00:05:15.930 --> 00:05:18.210
The electrons will leave
the group one elements

00:05:18.210 --> 00:05:20.840
and then they will go to the halogen.

00:05:20.840 --> 00:05:23.400
And in the process it might
release a lot of energy,

00:05:23.400 --> 00:05:25.850
but what you'd be left
with is an ionic compound.

00:05:25.850 --> 00:05:29.960
For example, lithium loses a electron

00:05:31.000 --> 00:05:33.260
and has a positive one charge.

00:05:33.260 --> 00:05:36.390
That positive ion would
be very attracted to

00:05:36.390 --> 00:05:39.940
a chlorine anion that has
just gained an electron.

00:05:39.940 --> 00:05:41.300
Maybe it's the same electron,

00:05:41.300 --> 00:05:44.370
or it swiped that electron
from another lithium atom.

00:05:44.370 --> 00:05:46.230
And so these two things would be attracted

00:05:46.230 --> 00:05:49.500
and they could form lithium chloride.

00:05:49.500 --> 00:05:52.360
And all of these alkali metals
could play that same role

00:05:52.360 --> 00:05:54.700
in this ionic compound as lithium.

00:05:54.700 --> 00:05:58.580
So it's also typical
to see sodium chloride.

00:05:58.580 --> 00:05:59.910
That is table salt.

00:05:59.910 --> 00:06:03.590
It's also typical to
see potassium chloride.

00:06:03.590 --> 00:06:05.180
So on and so forth.

00:06:05.180 --> 00:06:08.450
And on the other hand,
fluorine or bromine or iodine

00:06:08.450 --> 00:06:11.050
can play a similar role as chlorine.

00:06:11.050 --> 00:06:14.410
So you could see something
like sodium iodide

00:06:14.410 --> 00:06:16.600
or potassium iodide.

00:06:16.600 --> 00:06:20.580
Once again, the alkali metal
would have lost an electron,

00:06:20.580 --> 00:06:22.700
the halogen would have gained an electron,

00:06:22.700 --> 00:06:24.100
and then they're attracted to each other

00:06:24.100 --> 00:06:27.240
in forming these ionic compounds.

00:06:27.240 --> 00:06:29.410
What kind of ionic
compounds might be formed

00:06:29.410 --> 00:06:31.740
with these group two elements?

00:06:31.740 --> 00:06:33.500
Let's take calcium, for example.

00:06:33.500 --> 00:06:36.300
It's not unreasonable for
calcium to lose two electrons

00:06:36.300 --> 00:06:37.800
to have a stable outer shell,

00:06:37.800 --> 00:06:40.460
to have an electron
configuration like argon.

00:06:40.460 --> 00:06:43.460
So if it loses two electrons
it has a positive two charge.

00:06:43.460 --> 00:06:45.840
And you could imagine,
those two electrons get lost

00:06:45.840 --> 00:06:49.660
to two different iodine atoms.

00:06:49.660 --> 00:06:53.390
So each of them have a negative
one charge, so times two,

00:06:53.390 --> 00:06:56.170
and then what type of ionic
compound could they form?

00:06:56.170 --> 00:06:59.470
Well, you could have one
calcium and then two iodines.

00:06:59.470 --> 00:07:01.760
So calcium iodide is actually

00:07:01.760 --> 00:07:03.400
an ionic compound you would see.

00:07:03.400 --> 00:07:05.380
It has a neutral charge overall

00:07:05.380 --> 00:07:07.400
because calcium has a positive two charge

00:07:07.400 --> 00:07:09.970
and each of the iodines
have a negative one charge,

00:07:09.970 --> 00:07:13.600
but then you have two of them,
so it is neutral overall.

00:07:13.600 --> 00:07:15.760
What might calcium do with oxygen?

00:07:15.760 --> 00:07:17.870
Well, calcium likes to lose two electrons,

00:07:17.870 --> 00:07:20.490
oxygen likes to gain two electrons,

00:07:20.490 --> 00:07:24.210
so you could see something
like calcium oxide.

00:07:24.210 --> 00:07:26.220
So I will leave you there.

00:07:26.220 --> 00:07:30.030
The big picture here is, the
column in which an element is

00:07:30.030 --> 00:07:32.010
tells you a lot about its reactivity

00:07:32.010 --> 00:07:33.380
because it tells you in general

00:07:33.380 --> 00:07:35.360
how many valence electrons it has.

00:07:35.360 --> 00:07:40.360
And atoms are most stable when
they have a full outer shell

00:07:40.470 --> 00:07:42.890
and so that helps you predict,
hey, is it easier for them

00:07:42.890 --> 00:07:45.450
to lose electrons and form a positive ion

00:07:45.450 --> 00:07:47.630
or gain electrons and form a negative ion?

00:07:47.630 --> 00:07:49.860
And then from that, you
could make predictions

00:07:49.860 --> 00:07:51.710
as to the types of ionic compounds

00:07:51.710 --> 00:07:54.623
that could be formed with
the different elements.


Worked example: Identifying an element from successive ionization energies

WEBVTT
Kind: captions
Language: en

00:00:00.580 --> 00:00:02.159
- [Instructor] We are
told that the first five

00:00:02.159 --> 00:00:06.830
ionization energies for
a third period element

00:00:06.830 --> 00:00:08.970
are shown below.

00:00:08.970 --> 00:00:12.370
What is the identity of the element?

00:00:12.370 --> 00:00:13.570
So pause this video

00:00:13.570 --> 00:00:15.210
and see if you can
figure it out on your own

00:00:15.210 --> 00:00:17.310
and it'll probably be handy

00:00:17.310 --> 00:00:21.648
to have a periodic table of elements.

00:00:21.648 --> 00:00:24.910
So before I even look at a
periodic table of elements,

00:00:24.910 --> 00:00:26.800
let's make sure we
understand what this table

00:00:26.800 --> 00:00:27.890
is telling us.

00:00:27.890 --> 00:00:30.890
This is telling us that if
we start with a neutral atom

00:00:30.890 --> 00:00:32.270
of this mystery element,

00:00:32.270 --> 00:00:35.866
it would take 578 kilojoules per mole

00:00:35.866 --> 00:00:38.740
to remove that first electron

00:00:38.740 --> 00:00:41.570
to turn that atom into an ion

00:00:41.570 --> 00:00:45.480
with a plus one positive charge.

00:00:45.480 --> 00:00:50.480
And then, it would take another
1,817 kilojoules per mole

00:00:51.610 --> 00:00:54.210
to remove a second electron.

00:00:54.210 --> 00:00:57.230
So to make that ion even more positive.

00:00:57.230 --> 00:00:59.192
And then after that it would take another

00:00:59.192 --> 00:01:04.192
2,745 kilajoules per mole to
remove the third electron.

00:01:04.230 --> 00:01:06.240
And then to remove the fourth electron,

00:01:06.240 --> 00:01:08.780
it takes a way larger amount of energy.

00:01:08.780 --> 00:01:13.510
It takes 11,578 kilojoules per mole.

00:01:13.510 --> 00:01:15.740
And then the fifth
electron takes even more,

00:01:15.740 --> 00:01:19.350
14,842 kilojoules per mole.

00:01:19.350 --> 00:01:21.152
And so, for the first, second, and third

00:01:21.152 --> 00:01:24.120
you do have an increase
in ionization energy,

00:01:24.120 --> 00:01:26.530
but when you go to the
fourth the energy required

00:01:26.530 --> 00:01:28.750
to remove those is way higher.

00:01:28.750 --> 00:01:33.750
So to me, these look like you're
removing valence electrons

00:01:34.190 --> 00:01:39.150
and these look like you're
removing core electrons.

00:01:39.150 --> 00:01:40.830
So one way to think about it is

00:01:40.830 --> 00:01:43.280
let's look on our
periodic table of elements

00:01:43.280 --> 00:01:45.780
and look for a third period element

00:01:45.780 --> 00:01:48.960
that has three valence electrons.

00:01:48.960 --> 00:01:51.320
So we have our periodic table of elements.

00:01:51.320 --> 00:01:53.260
We want a third period element,

00:01:53.260 --> 00:01:55.260
so it's gonna be in this third row

00:01:55.260 --> 00:01:58.722
and which of these has
three valence electrons?

00:01:58.722 --> 00:02:01.350
Well, sodium has one valence electron,

00:02:01.350 --> 00:02:03.186
magnesium has two valence electrons,

00:02:03.186 --> 00:02:07.120
aluminum has three valence electrons.

00:02:07.120 --> 00:02:08.720
So one way to think about it is

00:02:08.720 --> 00:02:12.920
that first electron, it's a
reasonable ionization energy.

00:02:12.920 --> 00:02:14.191
Then the second one, a little higher.

00:02:14.191 --> 00:02:16.954
Then the third, a little
bit higher than after that,

00:02:16.954 --> 00:02:20.910
but then the fourth, you're
starting to go into the core.

00:02:20.910 --> 00:02:22.110
You're going to have to take an electron

00:02:22.110 --> 00:02:24.240
out of that full second energy shell,

00:02:24.240 --> 00:02:26.090
which takes a lot of energy.

00:02:26.090 --> 00:02:29.420
And so this is pretty clearly aluminum

00:02:29.420 --> 00:02:30.663
that is being described.


Groups of the periodic table

WEBVTT
Kind: captions
Language: en

00:00:00.350 --> 00:00:02.930
- [Instructor] So let's talk
a little bit about groups

00:00:02.930 --> 00:00:05.890
of the periodic table.

00:00:05.890 --> 00:00:08.550
Now, a very simple way
to think about groups

00:00:08.550 --> 00:00:12.210
is that they just are the
columns of the periodic table,

00:00:12.210 --> 00:00:14.670
and standard convention is to number them.

00:00:14.670 --> 00:00:16.940
This is the first column,
so that's group one,

00:00:16.940 --> 00:00:20.720
second column, third group,
fourth, fifth, sixth,

00:00:20.720 --> 00:00:25.720
seventh, eighth, group
nine, group 10, 11, 12,

00:00:27.860 --> 00:00:32.860
13, 14, 15, 16, 17, and 18.

00:00:33.870 --> 00:00:35.400
And I know some of
y'all might be thinking,

00:00:35.400 --> 00:00:37.460
what about these f-block
elements over here?

00:00:37.460 --> 00:00:39.400
If we were to properly
do the periodic table,

00:00:39.400 --> 00:00:41.000
we would shift all of these,

00:00:41.000 --> 00:00:44.350
everything from the d-block
and p-block rightwards,

00:00:44.350 --> 00:00:48.330
and make room for these f-block elements,

00:00:48.330 --> 00:00:50.950
but the convention is is
that we don't number them.

00:00:50.950 --> 00:00:53.030
But what's interesting, why
do we go through the trouble

00:00:53.030 --> 00:00:55.040
about calling one of these columns,

00:00:55.040 --> 00:00:57.960
of calling these columns a group?

00:00:57.960 --> 00:01:00.920
Well, this is what's interesting
about the periodic table,

00:01:00.920 --> 00:01:03.070
is that all of the elements in a column,

00:01:03.070 --> 00:01:05.690
for the most part, and
there's tons of exceptions,

00:01:05.690 --> 00:01:08.370
but for the most part,
the elements in the column

00:01:08.370 --> 00:01:11.070
have very very very similar properties,

00:01:11.070 --> 00:01:13.920
and that's because the
elements in a column,

00:01:13.920 --> 00:01:15.510
or the elements in a group,

00:01:15.510 --> 00:01:18.490
tend to have the same number of electrons

00:01:18.490 --> 00:01:19.870
in their outermost shell.

00:01:19.870 --> 00:01:22.530
They tend to have the same
number of valence electrons,

00:01:22.530 --> 00:01:25.140
and valence electrons and
electrons in the outermost shell,

00:01:25.140 --> 00:01:26.720
they tend to coincide, although,

00:01:26.720 --> 00:01:28.210
there's a slightly different variation.

00:01:28.210 --> 00:01:30.940
The valence electrons,
these are the electrons

00:01:30.940 --> 00:01:32.800
that are going to react,

00:01:32.800 --> 00:01:35.690
which tend to be the
outermost shell electrons,

00:01:35.690 --> 00:01:38.330
but there are exceptions to that,

00:01:38.330 --> 00:01:40.930
and there's actually a lot
of interesting exceptions

00:01:40.930 --> 00:01:43.710
that happen in the transition
metals, in the D block,

00:01:43.710 --> 00:01:45.310
but we're not gonna go into those details.

00:01:45.310 --> 00:01:46.530
Let's just think a little bit about

00:01:46.530 --> 00:01:49.040
some of the groups that
you will hear about,

00:01:49.040 --> 00:01:51.860
and why they react in very similar ways.

00:01:51.860 --> 00:01:53.840
So if we go with group one,

00:01:53.840 --> 00:01:55.360
group one, and hydrogen is a little bit

00:01:55.360 --> 00:01:57.260
of a strange character,

00:01:57.260 --> 00:01:58.560
because hydrogen isn't trying to get

00:01:58.560 --> 00:02:00.110
to eight valence electrons,

00:02:00.110 --> 00:02:01.400
hydrogen in that first shell

00:02:01.400 --> 00:02:05.230
just wants to get to two valence
electrons, like helium has,

00:02:05.230 --> 00:02:06.930
and so hydrogen is kind of,

00:02:06.930 --> 00:02:10.350
it's not, it doesn't
share as much in common

00:02:10.350 --> 00:02:11.670
with everything else in group one

00:02:11.670 --> 00:02:12.910
as you might expect for, say,

00:02:12.910 --> 00:02:15.100
all of the things in group two.

00:02:15.100 --> 00:02:17.430
Group one, if you put hydrogen aside,

00:02:17.430 --> 00:02:21.940
these are referred to
as the alkali metals,

00:02:21.940 --> 00:02:24.800
and hydrogen is not
considered an alkali metal,

00:02:24.800 --> 00:02:27.423
so these right over here are the alkali,

00:02:28.500 --> 00:02:30.103
alkali metals.

00:02:31.320 --> 00:02:34.560
Now why do all of these
have very similar reactions?

00:02:34.560 --> 00:02:36.750
Why do they have very similar properties?

00:02:36.750 --> 00:02:37.720
Well, to think about that,

00:02:37.720 --> 00:02:40.500
you just have to think about
their electron configurations.

00:02:40.500 --> 00:02:44.710
So, for example, the electron
configuration for lithium

00:02:44.710 --> 00:02:46.630
is going to be the same

00:02:46.630 --> 00:02:51.170
as the electron configuration of helium,

00:02:51.170 --> 00:02:53.470
of helium, and then,

00:02:53.470 --> 00:02:58.030
you're going to go to
your second shell, 2s1.

00:02:58.030 --> 00:02:59.820
It has one valence electron.

00:02:59.820 --> 00:03:03.650
It has one electron in
its outermost shell.

00:03:03.650 --> 00:03:04.993
What about sodium?

00:03:06.210 --> 00:03:09.210
Well, sodium is going to have the same

00:03:09.210 --> 00:03:12.003
electron configuration as neon,

00:03:13.260 --> 00:03:16.200
and then it's going to go 3s1,

00:03:16.200 --> 00:03:18.950
so once again, it has
one valence electron,

00:03:18.950 --> 00:03:21.240
one electron in its outermost shell.

00:03:21.240 --> 00:03:23.780
So all of these elements
in orange right over here,

00:03:23.780 --> 00:03:25.350
they have one valence electron,

00:03:25.350 --> 00:03:27.860
and they're trying to
get to the octet rule,

00:03:27.860 --> 00:03:30.880
this kind of stable nirvana for atoms,

00:03:30.880 --> 00:03:33.220
and so you can imagine is
that they're very reactive,

00:03:33.220 --> 00:03:35.190
and when they react, they tend to lose

00:03:35.190 --> 00:03:38.450
this electron in the outermost
shell, and that is the case.

00:03:38.450 --> 00:03:41.860
These alkali metals
are very very reactive,

00:03:41.860 --> 00:03:43.310
and actually, they have
very similar properties.

00:03:43.310 --> 00:03:46.790
They're shiny and soft, and actually,

00:03:46.790 --> 00:03:47.960
because they're so reactive,

00:03:47.960 --> 00:03:49.600
it's hard to find them where they haven't

00:03:49.600 --> 00:03:51.530
reacted with other things.

00:03:51.530 --> 00:03:53.960
Well, let's keep looking
at the other groups.

00:03:53.960 --> 00:03:57.410
Well, if we move one over to the right,

00:03:57.410 --> 00:04:00.410
this group two right over here,

00:04:00.410 --> 00:04:03.353
these are called the
alkaline earth metals.

00:04:04.266 --> 00:04:09.266
Alkaline, alkaline earth metals.

00:04:09.340 --> 00:04:13.880
And once again, they have
very similar properties,

00:04:13.880 --> 00:04:16.380
and that's because they
have two valence electrons,

00:04:16.380 --> 00:04:19.350
two electrons in their outermost shell,

00:04:19.350 --> 00:04:21.960
and also for them, not quite as reactive

00:04:21.960 --> 00:04:23.570
as the alkali metals,

00:04:23.570 --> 00:04:27.420
but let me write this,
alkaline earth metals,

00:04:27.420 --> 00:04:29.640
but for them it's easier
to lose two electrons

00:04:29.640 --> 00:04:31.860
than to try to gain six to get to eight,

00:04:31.860 --> 00:04:34.470
and so these tend to also
be reasonably reactive,

00:04:34.470 --> 00:04:38.920
and they react by losing
those two outer electrons.

00:04:38.920 --> 00:04:42.710
Now something interesting
happens as you go to the D-block,

00:04:42.710 --> 00:04:44.510
and we studied this when we looked

00:04:44.510 --> 00:04:46.270
at electron configurations,

00:04:46.270 --> 00:04:48.430
but if you look at the
electron configuration

00:04:48.430 --> 00:04:51.250
for say, scandium right over here,

00:04:51.250 --> 00:04:54.350
the electron, let me do it in magenta,

00:04:54.350 --> 00:04:57.420
the electron configuration for scandium,

00:04:57.420 --> 00:04:58.823
so scandium,

00:05:01.070 --> 00:05:02.430
scandium's electron configuration

00:05:02.430 --> 00:05:06.080
is going to be the same as argon,

00:05:06.080 --> 00:05:08.170
it's going to be argon.

00:05:08.170 --> 00:05:10.300
The aufbau principle would tell us

00:05:10.300 --> 00:05:12.150
that the electron configuration,

00:05:12.150 --> 00:05:15.860
we would have the 4s2 just like calcium,

00:05:15.860 --> 00:05:17.520
but by the aufbau principle,

00:05:17.520 --> 00:05:21.400
we would also have one electron in 3d.

00:05:21.400 --> 00:05:24.843
So it would be argon, then 3d1 4s2.

00:05:27.280 --> 00:05:30.670
And to get things in the
right order for our shells,

00:05:30.670 --> 00:05:34.510
let me put the 3d1 before the 4s2.

00:05:34.510 --> 00:05:37.320
And so when people think
about the aufbau principle,

00:05:37.320 --> 00:05:40.300
they imagine all of these d-block elements

00:05:40.300 --> 00:05:43.000
as somehow filling the d-block.

00:05:43.000 --> 00:05:45.980
Now as we know in other videos,
that's not exactly true,

00:05:45.980 --> 00:05:49.340
but when you're conceptualizing
the electron configuration

00:05:49.340 --> 00:05:51.270
it might be useful.

00:05:51.270 --> 00:05:54.600
Then you come over here and
you start filling the p-block.

00:05:54.600 --> 00:05:59.240
So for example, if you look
at the electron configuration

00:05:59.240 --> 00:06:01.810
for, let's say carbon,

00:06:01.810 --> 00:06:05.930
carbon is going to have the
same electron configuration

00:06:05.930 --> 00:06:09.410
as helium, as helium,

00:06:09.410 --> 00:06:12.450
and then you're going to
fill your s-block 2s2,

00:06:12.450 --> 00:06:13.503
and then 2p one 2.

00:06:15.695 --> 00:06:17.590
So 2p2.

00:06:17.590 --> 00:06:19.600
So how many valence
electrons does it have?

00:06:19.600 --> 00:06:21.700
Well, in its second shell,
its outermost shell,

00:06:21.700 --> 00:06:24.890
it has two plus two, it
has four valence electrons,

00:06:24.890 --> 00:06:28.180
and that's going to be true
for the things in this group,

00:06:28.180 --> 00:06:29.340
and because of that,

00:06:29.340 --> 00:06:34.120
carbon has similar bonding
behavior to silicon,

00:06:34.120 --> 00:06:36.120
to the other things in its group.

00:06:36.120 --> 00:06:38.630
And we can keep going on, you know,

00:06:38.630 --> 00:06:42.730
for example, oxygen, oxygen and sulfur,

00:06:42.730 --> 00:06:45.840
these would both want
to take two electrons

00:06:45.840 --> 00:06:48.620
from someone else because they
have six valence electrons,

00:06:48.620 --> 00:06:49.550
they want to get to eight,

00:06:49.550 --> 00:06:51.580
so they have similar bonding behavior.

00:06:51.580 --> 00:06:53.440
You go to this yellow
group right over here,

00:06:53.440 --> 00:06:55.490
these are the halogens.

00:06:55.490 --> 00:06:57.100
So there's a special name for them.

00:06:57.100 --> 00:06:59.650
These are the halogens.

00:06:59.650 --> 00:07:01.250
And these are highly reactive,

00:07:01.250 --> 00:07:03.030
because they have seven valence electrons.

00:07:03.030 --> 00:07:03.960
They would love nothing more

00:07:03.960 --> 00:07:06.250
than to get one more valence electron,

00:07:06.250 --> 00:07:07.610
so they love to react, in fact,

00:07:07.610 --> 00:07:09.080
they especially love to react

00:07:09.080 --> 00:07:11.850
with the alkali metals over here.

00:07:11.850 --> 00:07:16.150
And then finally, you get to
kind of your atomic nirvana

00:07:16.150 --> 00:07:18.520
in the noble gases here.

00:07:18.520 --> 00:07:20.900
And so the noble gases,
that's the other name

00:07:20.900 --> 00:07:25.900
for the group 18 elements, noble gases.

00:07:26.030 --> 00:07:28.560
And they all have the
very similar property

00:07:28.560 --> 00:07:29.710
of not being reactive.

00:07:29.710 --> 00:07:30.740
Why don't they react?

00:07:30.740 --> 00:07:32.600
They have filled their outermost shell.

00:07:32.600 --> 00:07:34.220
They don't find the need, they're noble,

00:07:34.220 --> 00:07:35.560
they're kind of above the fray,

00:07:35.560 --> 00:07:40.513
they don't find the need to
have to react with anyone else.


Introduction to photoelectron spectroscopy

WEBVTT
Kind: captions
Language: en

00:00:00.840 --> 00:00:01.690
- [Instructor] In this video,

00:00:01.690 --> 00:00:03.130
we're going to introduce ourselves

00:00:03.130 --> 00:00:06.570
to the idea of photoelectron spectroscopy.

00:00:06.570 --> 00:00:09.860
It's a way of analyzing
the electron configuration

00:00:09.860 --> 00:00:13.140
of a sample of a certain type of atom.

00:00:13.140 --> 00:00:16.080
And so what you'll often see

00:00:16.080 --> 00:00:18.550
and you might see something
like this on an exam,

00:00:18.550 --> 00:00:21.190
is a photoelectron spectrum

00:00:21.190 --> 00:00:22.800
that looks something like this.

00:00:22.800 --> 00:00:23.850
And so the first question is,

00:00:23.850 --> 00:00:25.865
well, what's even going on?

00:00:25.865 --> 00:00:26.940
How is this generated?

00:00:26.940 --> 00:00:28.820
Well, I'm not gonna go into the details,

00:00:28.820 --> 00:00:30.320
but the big picture is

00:00:30.320 --> 00:00:35.320
the analysis will be done by
taking a stream of that atom,

00:00:36.400 --> 00:00:38.770
and so that atom, there's an atom stream

00:00:38.770 --> 00:00:39.820
going in one direction,

00:00:39.820 --> 00:00:42.110
and then the other
direction, let me label this,

00:00:42.110 --> 00:00:44.290
so that's the atoms

00:00:44.290 --> 00:00:45.640
that we're trying to analyze,

00:00:45.640 --> 00:00:47.410
and then the other direction,

00:00:47.410 --> 00:00:50.410
you send high-energy photons

00:00:50.410 --> 00:00:54.280
that are going to bombard
those atoms, photons.

00:00:54.280 --> 00:00:56.380
Now these photons are high enough energy,

00:00:56.380 --> 00:00:58.860
in fact, they're typically x-ray photons

00:00:58.860 --> 00:01:00.830
so that when they collide,

00:01:00.830 --> 00:01:03.160
the photons are high enough energy

00:01:03.160 --> 00:01:06.240
to overcome the binding energy

00:01:06.240 --> 00:01:09.130
of even the core electrons

00:01:09.130 --> 00:01:12.450
and as those electrons get knocked out,

00:01:12.450 --> 00:01:13.740
they move away

00:01:13.740 --> 00:01:16.030
and they enter into a magnetic field

00:01:16.030 --> 00:01:18.030
that will deflect those electrons

00:01:18.030 --> 00:01:20.910
and then make them hit a detector.

00:01:20.910 --> 00:01:22.490
And so you can imagine

00:01:22.490 --> 00:01:25.550
the electrons that are
closer to the nucleus,

00:01:25.550 --> 00:01:28.200
those have the highest binding energy,

00:01:28.200 --> 00:01:31.490
and so more of that energy from the photon

00:01:31.490 --> 00:01:33.840
is going to be used to knock it off

00:01:33.840 --> 00:01:35.630
so less of it is going to be there

00:01:35.630 --> 00:01:36.580
for the kinetic energy,

00:01:36.580 --> 00:01:40.330
so those closer electrons
aren't going to get as far

00:01:40.330 --> 00:01:41.660
and the outer electrons,

00:01:41.660 --> 00:01:44.540
those have the lowest
electron binding energy.

00:01:44.540 --> 00:01:46.350
They're the easiest to knock off

00:01:46.350 --> 00:01:49.680
and so you have more
of the photon's energy

00:01:49.680 --> 00:01:52.290
is going to be transferred
into kinetic energy.

00:01:52.290 --> 00:01:54.830
And so they're going to get further away

00:01:54.830 --> 00:01:56.830
and they're going to hit the detector

00:01:56.830 --> 00:01:58.190
at a further point.

00:01:58.190 --> 00:02:02.590
And so one way to view
the photoelectron spectrum

00:02:02.590 --> 00:02:06.260
is it gives you a sense of
roughly how many electrons

00:02:06.260 --> 00:02:08.380
have various binding energies.

00:02:08.380 --> 00:02:10.940
And you can see that the
binding energy increases

00:02:10.940 --> 00:02:12.880
as we go to the left.

00:02:12.880 --> 00:02:15.020
Now the reason why this makes sense,

00:02:15.020 --> 00:02:18.350
the binding energy is
inversely proportional

00:02:18.350 --> 00:02:21.540
to how much kinetic energy
these electrons have

00:02:21.540 --> 00:02:24.400
as they actually get knocked off.

00:02:24.400 --> 00:02:27.940
And so this spike on our
spectrum at the extreme left,

00:02:27.940 --> 00:02:29.870
these are the innermost electrons,

00:02:29.870 --> 00:02:31.820
and then these would be
electrons further out

00:02:31.820 --> 00:02:33.840
with the next lower binding energy,

00:02:33.840 --> 00:02:35.630
and then lower binding energy after that.

00:02:35.630 --> 00:02:37.130
And so we can analyze this

00:02:37.130 --> 00:02:40.180
to actually come up with
the electron configuration

00:02:40.180 --> 00:02:43.770
of this mystery element right over here.

00:02:43.770 --> 00:02:44.980
What do you think that would be?

00:02:44.980 --> 00:02:47.970
Pause this video and
try to think about that.

00:02:47.970 --> 00:02:49.240
Well as I mentioned,

00:02:49.240 --> 00:02:51.900
this spike right over
here would correspond

00:02:51.900 --> 00:02:54.480
to detecting the innermost electrons,

00:02:54.480 --> 00:02:56.730
and so the innermost electrons

00:02:56.730 --> 00:02:59.400
are the one S electrons,

00:02:59.400 --> 00:03:01.920
and we know that those
aren't the only electrons

00:03:01.920 --> 00:03:05.300
'cause there's electrons that
have lower binding energies,

00:03:05.300 --> 00:03:07.470
and so we know that would have filled up

00:03:07.470 --> 00:03:09.500
that innermost shell

00:03:09.500 --> 00:03:13.630
and so we know that they
have two one S electrons

00:03:13.630 --> 00:03:16.680
and then we can then think
that this next spike,

00:03:16.680 --> 00:03:18.220
that's going to be the two S electrons

00:03:18.220 --> 00:03:20.090
and we have more electrons than that

00:03:20.090 --> 00:03:23.090
so we must have filled
up the two S sub shell

00:03:23.090 --> 00:03:24.760
and then this next spike,

00:03:24.760 --> 00:03:26.350
this looks like two P.

00:03:26.350 --> 00:03:28.680
And the reason why this
really makes a lot of sense is

00:03:28.680 --> 00:03:31.880
notice the detector is
detecting more electrons there,

00:03:31.880 --> 00:03:33.790
and we also have more electrons,

00:03:33.790 --> 00:03:35.590
and so that must have been filled

00:03:35.590 --> 00:03:36.423
and that makes sense,

00:03:36.423 --> 00:03:37.780
and actually the way this was constructed,

00:03:37.780 --> 00:03:39.630
it's not always going to be this perfect,

00:03:39.630 --> 00:03:42.510
but you can see you have roughly
three times as many two P

00:03:42.510 --> 00:03:45.830
electrons as two S
electrons, which makes sense.

00:03:45.830 --> 00:03:48.230
The two P sub shell can fit six electrons.

00:03:48.230 --> 00:03:50.600
Two S sub shell fits two.

00:03:50.600 --> 00:03:52.560
So this next spike is going

00:03:52.560 --> 00:03:55.030
to be the next highest energy shell,

00:03:55.030 --> 00:03:57.400
which is going to have
a lower binding energy.

00:03:57.400 --> 00:03:58.650
It's easy to knock the,

00:03:58.650 --> 00:04:01.270
it's easier to knock those electrons off.

00:04:01.270 --> 00:04:04.710
And so this looks like it's
going to be the three S two

00:04:04.710 --> 00:04:06.400
and then this next spike,

00:04:06.400 --> 00:04:09.480
this looks like three P six

00:04:09.480 --> 00:04:12.370
and then that one gets completely filled

00:04:12.370 --> 00:04:14.620
and we have one more spike after that

00:04:14.620 --> 00:04:17.310
and that spike seems to
get roughly the same number

00:04:17.310 --> 00:04:21.320
of electrons as all of
the other S sub shells

00:04:21.320 --> 00:04:23.450
and we know from the Aufbau principle

00:04:23.450 --> 00:04:25.410
that the next we fill is four S

00:04:25.410 --> 00:04:27.440
and it looks like there's
two electrons there

00:04:27.440 --> 00:04:29.170
because this spike is about the same

00:04:29.170 --> 00:04:31.890
as the other filled S sub shells.

00:04:31.890 --> 00:04:33.210
And so just like that,

00:04:33.210 --> 00:04:35.990
we're able to use a photoelectron spectrum

00:04:35.990 --> 00:04:37.670
to come up with the electron configuration

00:04:37.670 --> 00:04:39.100
of this mystery element.

00:04:39.100 --> 00:04:41.520
Its electron configuration is one S two,

00:04:41.520 --> 00:04:42.930
two S two,

00:04:42.930 --> 00:04:44.560
two P six,

00:04:44.560 --> 00:04:46.010
three S two,

00:04:46.010 --> 00:04:48.360
three P six,

00:04:48.360 --> 00:04:49.720
four S two.

00:04:49.720 --> 00:04:52.710
And what element has this
electron configuration?

00:04:52.710 --> 00:04:54.280
Well, we've worked on it in other videos,

00:04:54.280 --> 00:04:56.810
but I can get my periodic
table of elements out,

00:04:56.810 --> 00:04:58.340
and we can see, let's see.

00:04:58.340 --> 00:05:00.300
One S two gets us to helium,

00:05:00.300 --> 00:05:03.920
then you have two S two,
two P six gets us to neon.

00:05:03.920 --> 00:05:07.200
Three S two, three P six gets us to argon,

00:05:07.200 --> 00:05:10.650
and then four S two gets us to calcium.

00:05:10.650 --> 00:05:13.640
So our mystery element is

00:05:14.710 --> 00:05:15.740
calcium,

00:05:15.740 --> 00:05:18.130
and if someone were to ask
about valence electrons,

00:05:18.130 --> 00:05:21.190
that would be this outermost
spike right over here.

00:05:21.190 --> 00:05:24.920
The spike of electrons with
the lowest binding energy.

00:05:24.920 --> 00:05:26.150
They have the lowest binding energy

00:05:26.150 --> 00:05:27.530
because they're the furthest out there.

00:05:27.530 --> 00:05:29.860
They are the easiest to knock off,

00:05:29.860 --> 00:05:31.883
and because they're the
easiest to knock off,

00:05:31.883 --> 00:05:34.760
most of that photon energy is leftover

00:05:34.760 --> 00:05:37.500
after overcoming the binding energy

00:05:37.500 --> 00:05:39.420
that gets converted into kinetic energy.

00:05:39.420 --> 00:05:42.603
So those electrons get deflected further.

00:05:43.480 --> 00:05:45.160
And the base of what we see here

00:05:45.160 --> 00:05:47.170
are the photoelectron spectrum of calcium.

00:05:47.170 --> 00:05:50.700
What would we expect the
photoelectron spectrum

00:05:50.700 --> 00:05:52.610
of potassium be?

00:05:52.610 --> 00:05:55.200
And just as a reminder,

00:05:55.200 --> 00:05:57.370
potassium has an atomic number of 19,

00:05:57.370 --> 00:06:00.350
so it has 19 protons in the nucleus,

00:06:00.350 --> 00:06:03.200
while calcium has 20
protons in the nucleus,

00:06:03.200 --> 00:06:04.903
and we're going to assume

00:06:04.903 --> 00:06:06.420
that we're talking a
neutral potassium atom,

00:06:06.420 --> 00:06:09.110
so it's going to have
19 electrons, as well.

00:06:09.110 --> 00:06:10.790
Pause this video and think about

00:06:10.790 --> 00:06:12.640
how it might be different.

00:06:12.640 --> 00:06:13.810
When we think about potassium,

00:06:13.810 --> 00:06:16.930
it's going to have a very
similar photoelectron spectrum

00:06:16.930 --> 00:06:18.180
as calcium,

00:06:18.180 --> 00:06:21.760
but because it only has
19 versus 20 protons,

00:06:21.760 --> 00:06:24.470
it has less positive
charge in the nucleus,

00:06:24.470 --> 00:06:27.290
so it pulls a little bit less hard

00:06:27.290 --> 00:06:29.130
on our various shells.

00:06:29.130 --> 00:06:30.180
So in potassium,

00:06:30.180 --> 00:06:32.250
you're still going to have one S two,

00:06:32.250 --> 00:06:34.810
but it's going to have a
slightly lower binding energy

00:06:34.810 --> 00:06:38.040
because it's not pulled
into the nucleus as much.

00:06:38.040 --> 00:06:39.370
And I'm not drawing it perfectly.

00:06:39.370 --> 00:06:40.280
It might not be this much.

00:06:40.280 --> 00:06:41.910
Actually, you know what?

00:06:41.910 --> 00:06:43.138
It's probably more slight, probably.

00:06:43.138 --> 00:06:43.971
Something like this,

00:06:43.971 --> 00:06:45.710
but it's going to be a
little bit to the right.

00:06:45.710 --> 00:06:48.460
Similarly, two S two is
going to be a little bit

00:06:48.460 --> 00:06:50.010
to the right,

00:06:50.010 --> 00:06:53.730
and then two P six is
going to be a little bit

00:06:53.730 --> 00:06:54.563
to the right,

00:06:54.563 --> 00:06:57.080
and once again, I'm not
drawing it completely perfectly

00:06:57.080 --> 00:06:58.530
'cause I don't have the exact data here.

00:06:58.530 --> 00:06:59.660
Three S two

00:06:59.660 --> 00:07:02.410
would be a little bit to the right.

00:07:02.410 --> 00:07:03.293
Once again,

00:07:04.775 --> 00:07:05.608
only 19 protons versus 20 for calcium,

00:07:05.608 --> 00:07:07.890
so we're pulling a
little bit less inwards,

00:07:07.890 --> 00:07:10.060
so we have a lower binding energy

00:07:10.060 --> 00:07:12.210
for any given shell or sub shell,

00:07:12.210 --> 00:07:16.600
and three P six is going to
be a little bit to the right,

00:07:16.600 --> 00:07:17.780
like this,

00:07:17.780 --> 00:07:20.940
and then what is the four S
sub shell going to look like?

00:07:20.940 --> 00:07:23.990
Well, it doesn't have two
electrons in the four S sub shell.

00:07:23.990 --> 00:07:24.950
It only has one,

00:07:24.950 --> 00:07:27.710
'cause it only has 19
electrons and not 20.

00:07:27.710 --> 00:07:30.160
And so it's going to be a
little bit to the right.

00:07:30.160 --> 00:07:32.320
It has a lower binding energy

00:07:32.320 --> 00:07:33.720
and it's only going to be half as high

00:07:33.720 --> 00:07:35.900
because you only have
one electron, not two.

00:07:35.900 --> 00:07:38.810
So it's going to look something like that.

00:07:38.810 --> 00:07:41.480
That would be the photoelectron spectrum

00:07:41.480 --> 00:07:43.720
of potassium, roughly speaking.

00:07:43.720 --> 00:07:46.380
Now we've already talked about
that your outermost shell

00:07:46.380 --> 00:07:48.160
shows where your valence electrons are.

00:07:48.160 --> 00:07:49.530
So if we're thinking about potassium,

00:07:49.530 --> 00:07:51.460
it would be right over there.

00:07:51.460 --> 00:07:52.730
Now that also tells us,

00:07:52.730 --> 00:07:54.570
when we're thinking about
the binding energy over here,

00:07:54.570 --> 00:07:56.110
so this binding energy,

00:07:56.110 --> 00:07:59.110
that tells us how much energy do we need

00:07:59.110 --> 00:08:01.320
to remove an electron?

00:08:01.320 --> 00:08:03.820
And so when you're removing
that first electron,

00:08:03.820 --> 00:08:06.300
that's your first ionization energy.

00:08:06.300 --> 00:08:08.340
Once you remove that first electron,

00:08:08.340 --> 00:08:10.900
because of all of the interactions
between the electrons,

00:08:10.900 --> 00:08:13.920
your photoelectron spectrum would change

00:08:13.920 --> 00:08:16.135
so you can't think about your second

00:08:16.135 --> 00:08:17.120
or third ionization energies,

00:08:17.120 --> 00:08:18.910
but your first ionization energy,

00:08:18.910 --> 00:08:20.980
you just have to think about
it's the binding energy

00:08:20.980 --> 00:08:22.653
of your outermost electrons.


The Aufbau principle

WEBVTT
Kind: captions
Language: en

00:00:00.870 --> 00:00:03.210
- [Instructor] In other
videos we introduced ourselves

00:00:03.210 --> 00:00:05.240
to the idea of orbitals

00:00:05.240 --> 00:00:08.900
and these are various orbitals
in their various subshells

00:00:08.900 --> 00:00:12.560
that you could find in
various shells of an atom.

00:00:12.560 --> 00:00:14.750
And in this video we're gonna
get a little bit more practice

00:00:14.750 --> 00:00:16.080
with electron configuration.

00:00:16.080 --> 00:00:18.384
In particular, we're
going to expose ourselves

00:00:18.384 --> 00:00:21.670
to the idea of the Aufbau principle.

00:00:21.670 --> 00:00:23.580
Now Aufbau comes from German.

00:00:23.580 --> 00:00:25.800
It means the building principle.

00:00:25.800 --> 00:00:27.210
It's a very useful way

00:00:27.210 --> 00:00:31.700
of thinking about electron
configurations past calcium.

00:00:31.700 --> 00:00:33.600
Let's just a get little bit warmed up.

00:00:33.600 --> 00:00:37.540
What is the electron
configuration of neon?

00:00:37.540 --> 00:00:39.280
Pause this video and think about it

00:00:39.280 --> 00:00:41.980
and as a hint I will give
you the periodic table here.

00:00:42.820 --> 00:00:45.800
All right, well neon has
an atomic number of 10

00:00:45.800 --> 00:00:48.540
and if we're talking
about a neutral neon atom

00:00:48.540 --> 00:00:50.310
it's gonna have 10 electrons.

00:00:50.310 --> 00:00:54.230
And so, the first two will
that fill that first shell.

00:00:54.230 --> 00:00:59.230
So we have 1s2 and then, the
next two are going to fill

00:00:59.769 --> 00:01:03.970
the 2s subshell in your second shell.

00:01:03.970 --> 00:01:05.470
So then you're gonna have 2s2.

00:01:06.950 --> 00:01:11.000
And then we have six more
electrons to get to 10

00:01:11.000 --> 00:01:15.187
and that's now going to fill
your 2p subshell, so 2p6.

00:01:17.790 --> 00:01:19.900
And so what's the order of the subshells

00:01:19.900 --> 00:01:21.160
that we just filled?

00:01:21.160 --> 00:01:25.503
Well, first we filled
1s, then we filled 2s,

00:01:26.800 --> 00:01:28.220
then we filled 2p

00:01:29.680 --> 00:01:32.870
and you can also see that in
the periodic table of elements.

00:01:32.870 --> 00:01:36.840
In this first row, you're
filling that first shell.

00:01:36.840 --> 00:01:40.300
In this second row or this second period,

00:01:40.300 --> 00:01:44.110
you are filling that second shell.

00:01:44.110 --> 00:01:47.693
Now what's going to happen if
we were to go to say, argon?

00:01:48.600 --> 00:01:50.150
So if you're going to go to argon,

00:01:50.150 --> 00:01:52.730
what will that electron
configuration look like?

00:01:52.730 --> 00:01:55.047
Pause the video and think about that.

00:01:55.047 --> 00:01:58.530
Well, we can use the
noble gas configuration

00:01:58.530 --> 00:01:59.800
or the noble gas notation.

00:01:59.800 --> 00:02:00.700
We could say, all right we're going to be

00:02:00.700 --> 00:02:02.890
building off of neon.

00:02:02.890 --> 00:02:05.650
So we're gonna have the
electron configuration of neon,

00:02:05.650 --> 00:02:09.200
but then we're going to add
electrons into our third shell.

00:02:09.200 --> 00:02:11.720
So from neon we would
then add two electrons

00:02:11.720 --> 00:02:15.190
into the 3s subshell, 3s2.

00:02:16.100 --> 00:02:18.610
And then, to get to 18 electrons,

00:02:18.610 --> 00:02:19.550
we're at 12 right now,

00:02:19.550 --> 00:02:21.600
we're gonna have six
more that are going to be

00:02:21.600 --> 00:02:26.395
in the 3p subshell, so 3p6.

00:02:26.395 --> 00:02:28.950
So, on this diagram over here

00:02:28.950 --> 00:02:31.950
we went from 2s to 2p to fill up neon

00:02:31.950 --> 00:02:33.380
and then as we went to argon

00:02:33.380 --> 00:02:35.333
we go to 3s to 3p.

00:02:39.030 --> 00:02:42.510
Now what would be the electron
configuration of calcium?

00:02:42.510 --> 00:02:45.090
Pause the video and think about it.

00:02:45.090 --> 00:02:48.140
All right, well calcium has 20 protons.

00:02:48.140 --> 00:02:51.010
So a neutral calcium
would have 20 electrons.

00:02:51.010 --> 00:02:53.010
So two more electrons than argon.

00:02:53.010 --> 00:02:55.600
So we can build off of argon

00:02:55.600 --> 00:02:59.480
and where are those electrons going to go?

00:02:59.480 --> 00:03:02.940
And this is where the Aufbau
principle is interesting.

00:03:02.940 --> 00:03:06.890
There is indeed a 3d subshell,

00:03:06.890 --> 00:03:08.300
but in the case of calcium

00:03:08.300 --> 00:03:12.280
instead of those two electrons
being in the 3d subshell,

00:03:12.280 --> 00:03:16.720
they end up in the 4s subshell.

00:03:16.720 --> 00:03:21.120
So calcium's electron
configuration is the same as argon

00:03:21.120 --> 00:03:25.450
and instead of it being
3d2 here on top of that

00:03:25.450 --> 00:03:29.750
it goes straight to 4s2.

00:03:29.750 --> 00:03:32.580
And so that's why I was
drawing this diagram like this

00:03:32.580 --> 00:03:33.680
and you'll often see that

00:03:33.680 --> 00:03:35.720
in an introductory chemistry class.

00:03:35.720 --> 00:03:38.360
You fill 1s first, no surprises.

00:03:38.360 --> 00:03:40.130
You're filling in that first shell.

00:03:40.130 --> 00:03:41.443
Then you fill 2s.

00:03:42.350 --> 00:03:45.720
Then you fill 2p and you
filled your second shell.

00:03:45.720 --> 00:03:48.500
Then you go to 3s, once
again no surprises.

00:03:48.500 --> 00:03:50.210
Then you go to 3p.

00:03:50.210 --> 00:03:51.380
Now this is the surprise

00:03:51.380 --> 00:03:53.810
and why this Aufbau diagram is useful.

00:03:53.810 --> 00:03:55.680
For electron configuration purposes,

00:03:55.680 --> 00:03:57.720
if you're thinking about
potassium or calcium,

00:03:57.720 --> 00:04:02.113
the extra electrons are now
going to go in the 4s subshell.

00:04:04.470 --> 00:04:07.240
So now let's think about what
the electron configuration

00:04:07.240 --> 00:04:09.640
of the scandium would be.

00:04:09.640 --> 00:04:12.650
Pause this video and think about that.

00:04:12.650 --> 00:04:14.850
Well scandium has one
more proton than calcium.

00:04:14.850 --> 00:04:17.580
It has 21 protons and if it is neutral,

00:04:17.580 --> 00:04:19.600
it's also gonna have one more electron

00:04:19.600 --> 00:04:22.240
relative to a neutral calcium atom.

00:04:22.240 --> 00:04:25.710
And so, it could have a
similar electron configuration.

00:04:25.710 --> 00:04:28.170
So we could base it off of argon.

00:04:28.170 --> 00:04:32.270
We have two electrons in the 4s subshell,

00:04:32.270 --> 00:04:33.193
so I'll write 4s2

00:04:35.000 --> 00:04:37.536
and the Aufbau principle
would describe that

00:04:37.536 --> 00:04:40.480
and the Aufbau principle,
this little diagram,

00:04:40.480 --> 00:04:43.810
would say, all right that
other electron is going to be

00:04:43.810 --> 00:04:47.447
in the 3d subshell, so you do 3d1.

00:04:48.774 --> 00:04:52.450
And this is indeed an accurate
electron configuration

00:04:52.450 --> 00:04:53.892
for scandium.

00:04:53.892 --> 00:04:56.790
Now if the Aufbau
principle makes you think

00:04:56.790 --> 00:04:58.890
that you're filling 4s first

00:04:58.890 --> 00:05:01.510
and then you are starting to fill 3d,

00:05:01.510 --> 00:05:04.980
if you were actually
building up a scandium atom,

00:05:04.980 --> 00:05:07.410
and that's actually taught
in most chemistry books

00:05:07.410 --> 00:05:08.384
and in most classes,

00:05:08.384 --> 00:05:12.080
but actually if people start
with the scandium nucleus

00:05:12.080 --> 00:05:14.530
that has 18 electrons.

00:05:14.530 --> 00:05:16.750
So that would have a positive charge,

00:05:16.750 --> 00:05:18.350
when they add that first electron

00:05:18.350 --> 00:05:20.061
it actually does not go to 4s.

00:05:20.061 --> 00:05:22.570
It goes to 3d.

00:05:22.570 --> 00:05:25.250
So this electron actually
gets added first.

00:05:25.250 --> 00:05:27.750
If you're actually
thinking about building.

00:05:27.750 --> 00:05:29.730
But I don't want to confuse you too much.

00:05:29.730 --> 00:05:31.370
In this video we're just thinking about

00:05:31.370 --> 00:05:33.000
the electron configuration

00:05:33.000 --> 00:05:36.062
and for that Aufbau can be very useful.

00:05:36.062 --> 00:05:38.912
Now for electron configuration purposes,

00:05:38.912 --> 00:05:43.912
3d, you then go to 4p, and
then you then go to 5s,

00:05:45.240 --> 00:05:48.630
and that's why you might
see this type of a diagram,

00:05:48.630 --> 00:05:52.610
once again, in your traditional
first year chemistry books.

00:05:52.610 --> 00:05:56.390
So the big takeaway here
is the Aufbau principle

00:05:56.390 --> 00:05:58.440
that you'll learn, this type of diagram,

00:05:58.440 --> 00:06:00.573
it's useful for electron configuration

00:06:00.573 --> 00:06:03.060
and it might be useful to think about it

00:06:03.060 --> 00:06:06.466
as you're building these
atoms electron by electron,

00:06:06.466 --> 00:06:09.336
but if you really want
the precise accurate truth

00:06:09.336 --> 00:06:11.610
once you get beyond calcium

00:06:11.610 --> 00:06:13.490
it gets a little bit more complicated.

00:06:13.490 --> 00:06:16.250
Now one other thing that
I want you to appreciate

00:06:16.250 --> 00:06:18.740
based on what we just learned is patterns

00:06:18.740 --> 00:06:20.940
in the periodic table of elements.

00:06:20.940 --> 00:06:24.640
So for which elements are we
building out our S subshell?

00:06:24.640 --> 00:06:28.900
Well, you could see that
for all of these elements

00:06:28.900 --> 00:06:30.820
right over here,

00:06:30.820 --> 00:06:32.180
these first two columns,

00:06:32.180 --> 00:06:34.640
we're building out our S subshell.

00:06:34.640 --> 00:06:36.900
Now it looks like
something is missing there.

00:06:36.900 --> 00:06:39.300
Is there something else that
builds out our S subshell?

00:06:39.300 --> 00:06:41.130
Well, from that point of
view we could actually think

00:06:41.130 --> 00:06:43.250
of helium as being right over here

00:06:43.250 --> 00:06:46.630
'cause helium, we're
building out that 1s subshell

00:06:46.630 --> 00:06:50.210
and because of that all of
these elements right over here,

00:06:50.210 --> 00:06:53.063
we say that they are in the S block.

00:06:54.170 --> 00:06:58.207
Now, which elements are
building out their P subshells?

00:06:58.207 --> 00:07:02.960
Well, all of these
elements right over here

00:07:02.960 --> 00:07:05.510
are building out their P subshells

00:07:05.510 --> 00:07:07.340
or have it fully built out.

00:07:07.340 --> 00:07:09.620
And because of that,
all of these elements,

00:07:09.620 --> 00:07:13.000
we call these the P block.

00:07:13.000 --> 00:07:15.680
And these elements in the
middle right over here,

00:07:15.680 --> 00:07:17.690
scandium is one of them,

00:07:17.690 --> 00:07:20.253
they are called the D block.

00:07:21.160 --> 00:07:24.270
Now one reason why folks might
have called it the D block

00:07:24.270 --> 00:07:26.920
is if you really imagine
the Aufbau principle

00:07:26.920 --> 00:07:28.610
as building up atoms,

00:07:28.610 --> 00:07:30.100
it might be tempting to say,

00:07:30.100 --> 00:07:33.040
oh well we're building
in the fourth row here,

00:07:33.040 --> 00:07:35.290
we're building the 3d subshell

00:07:35.290 --> 00:07:38.090
or in the fifth row here we're
building the 4d subshell.

00:07:39.040 --> 00:07:41.663
Now we now know that
that actually isn't true,

00:07:41.663 --> 00:07:44.680
but from electron
configuration point of view

00:07:44.680 --> 00:07:46.890
it can appear that way

00:07:46.890 --> 00:07:50.420
and so that's why it is called the D block

00:07:50.420 --> 00:07:51.793
and I will leave you there.