Predicting bond type (electronegativity)

WEBVTT
Kind: captions
Language: en

00:00:00.180 --> 00:00:02.120
- In other videos, we had started talking

00:00:02.120 --> 00:00:04.520
about the types of bonds that might form

00:00:04.520 --> 00:00:06.890
between atoms of a given element.

00:00:06.890 --> 00:00:11.830
For example, if you have
two metals forming a bond,

00:00:11.830 --> 00:00:15.700
well, you are going to
have a metallic bond.

00:00:15.700 --> 00:00:18.623
If you have two nonmetals,

00:00:21.756 --> 00:00:24.232
engaged in some type of bonding activity,

00:00:24.232 --> 00:00:27.802
this is likely to be a covalent bond.

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And the general rule of thumb is

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if you have one metal,

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and one nonmetal,

00:00:38.970 --> 00:00:41.840
that this is likely to be an ionic bond.

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These are the general rules of thumb.

00:00:44.160 --> 00:00:46.850
What I wanna do in this
video is to better appreciate

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that bonding is really more of a spectrum.

00:00:50.270 --> 00:00:51.200
There are bonds,

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and we've talked about things
like polar covalent bonds,

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that start to look a
little bit more and more

00:00:56.190 --> 00:00:57.570
ionic in nature.

00:00:57.570 --> 00:00:59.899
And so that's what we're
gonna talk about in this video

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and think about it in the
context of electronegativity.

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Just as a reminder, we talk
about electronegativity

00:01:06.180 --> 00:01:07.630
in many videos,

00:01:07.630 --> 00:01:11.140
but this is the property
of an atom that's in a bond

00:01:11.140 --> 00:01:12.700
to hog electrons,

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to want the electron
density to be closer to it

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for the electron pairs to spend more time

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around that particular atom.

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So, something with a
high electronegativity

00:01:23.670 --> 00:01:26.660
is going to be greedier with the electrons

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than something with a
low electronegativity.

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We can think about the spectrum between

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at this end you have ionic,

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and at this end you have covalent.

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And one way to think about it
is at the extreme left end,

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you don't have much difference
in electronegativities.

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Both atoms that are
participating in the bond

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are roughly equal in how
badly they want the electrons.

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While in an ionic bond,

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you have a very big difference
in electronegativities,

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so much so that one of the
atoms swipes an electron

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from the other.

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So, one way to think about it is,

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let me draw a little bit of an arrow here,

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so this is increased electronegativity

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difference as you go from left to right.

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And some place in the middle,

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or as you go from left to right,

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you're becoming more
and more polar covalent.

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So for example, if you have a bond

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between oxygen and hydrogen,

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these are both nonmetals.

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So this will be a covalent bond

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by just our general rule of thumb.

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And actually the division
between metals and nonmetals,

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I'm gonna make it right over here,

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it's this blue line is one
division you could view,

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although things that straddle it

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are a little bit more interesting.

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But oxygen and hydrogen
are both nonmetals,

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but you have a pretty big
difference in electronegativities.

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This right over here is electronegativity

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measured on a Pauling scale,

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named after the famous biologist
and chemist, Linus Pauling,

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and you can see on that
scale oxygen is a 3.44,

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one of the most electronegative atoms.

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Electronegativity trends, we
talk about in other videos,

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goes from bottom left to top right.

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The things at the top right
that are not the noble gases,

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these are the ones that really
are greedy with electrons.

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And oxygen is one of the greediest.

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While hydrogen, it's
not not electronegative,

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but it's lower, at 2.20.

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So in this scenario,

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those electrons are
going to spend more time

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around the oxygen.

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If they spent an equal amount of time,

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that oxygen might be neutral,

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but since they're spending
a little bit more time here,

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we'll say that has a
partial negative charge,

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the Greek lowercase letter delta,

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and on the hydrogen side

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because the shared electrons
are spending more time

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around the oxygen than
around the hydrogen,

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you would have a partially
positive charge right over there.

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And so this would be
a polar covalent bond.

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Maybe on the spectrum it
sits right over there,

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depending on how you wanna,

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how you view this scale.

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Now the other question you say is

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okay, this is a spectrum
between covalent and ionic,

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what about metallic?

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Well, metallic bonds are in
general going to be formed

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if you have two things
that are not so different

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in electronegativity,

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and they both have reasonably
low electronegativities.

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So that's why things on the
bottom left right over here,

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if you have two of these forming bonds

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with each other somehow,

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that you're likely to have metallic bonds.

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And that makes sense
because in metallic bonds

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you have all the electrons
kind of mixing in

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in a shared pool,

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which gives some of the
properties like conductivity.

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And so if you have a lot of things

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that are fairly similar
in electronegativity,

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and they're all low in electronegativity,

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they might be more willing to
share those valence electrons

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in a communal pool.


Predicting bond type (metals vs. nonmetals)

WEBVTT
Kind: captions
Language: en

00:00:00.480 --> 00:00:01.450
- [Instructor] In a previous video,

00:00:01.450 --> 00:00:06.270
we introduced ourselves to the
idea of bonds between atoms,

00:00:06.270 --> 00:00:08.500
and we talked about the types of bonds,

00:00:08.500 --> 00:00:11.140
ionic, covalent

00:00:12.240 --> 00:00:14.210
and metallic.

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In this video we're going
to dig a little bit deeper

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and talk about the types of bonds

00:00:18.530 --> 00:00:22.350
that are likely to be formed
between different elements.

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And to understand that,
I'm going to introduce

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a broad classification of the elements,

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and in general, we're just
going to think about things

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as metals and as nonmetals.

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So before I even point out on
the periodic table of elements

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what are the metals and
what are the nonmetals

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and maybe what are the
ones that are in between,

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what are the properties of metals?

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Well, generally speaking,
they conduct electricity.

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Conduct electricity.

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They tend to be malleable,
which is just a fancy way

00:00:56.860 --> 00:00:59.610
of saying that you can
bend them without breaking.

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And generally speaking, and
there's exceptions to this,

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they are solid at room temperature.

00:01:05.590 --> 00:01:10.590
So I'll say solid at room temperature.

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Now what do you think the properties

00:01:13.240 --> 00:01:14.730
of nonmetals are going to be?

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Well generally speaking,

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they're going to be the opposite of this.

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Nonmetals, generally speaking,

00:01:20.240 --> 00:01:23.090
at room temperature are often not solid,

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they're often times gasses.

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They are not going to
conduct electricity well.

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Now when you look at a
periodic table of elements,

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how do you divide the
metals from the nonmetals?

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Well that's what this
little scratchy yellow line

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I'm drawing is trying to indicate.

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So everything above and to
the right of this yellow line

00:01:43.310 --> 00:01:46.410
is a nonmetal and if you
look at the color code

00:01:46.410 --> 00:01:48.750
from the folks who made this
periodic table of elements,

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everything in this yellow
color that we have here,

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so hydrogen and carbon and nitrogen

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and oxygen and fluorine,
chlorine, I could keep going,

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these are all nonmetals.

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And it is the case that generally speaking

00:02:02.330 --> 00:02:05.520
at room temperature, they
will be in a gas form

00:02:05.520 --> 00:02:08.560
and they will not
conduct electricity well.

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These things in blue we've
talked about in other videos,

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these are the noble gasses.

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So these are also nonmetals.

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The people who made this
periodic table of elements

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put them in their own color

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'cause then you could view
them as a subclass of nonmetals

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and they tend to be very inert,

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they don't interact with other things.

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They don't tend to form
any of these bonds.

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Now everything else, you can consider

00:02:32.740 --> 00:02:36.490
in some form to be a metal

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and the reason why this
periodic table of elements

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has different colors is that
there's subclassifications

00:02:41.690 --> 00:02:43.110
of the metals

00:02:43.110 --> 00:02:45.500
but generally speaking,
all of these things

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that you see right over here

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below this scratchy yellow line

00:02:49.820 --> 00:02:51.870
have the properties, generally speaking,

00:02:51.870 --> 00:02:54.220
of conducting electricity,
being malleable,

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being solid at room temperature.

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And these things that straddle

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this yellow line right over here,

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these things that are in this kind

00:03:01.270 --> 00:03:03.790
of bluish-green kind of color,

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these are sometimes viewed as metalloids

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because they have some
properties of metals

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and some properties of nonmetals.

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But generally speaking,
if you know whether

00:03:13.170 --> 00:03:15.830
the things reacting are
metals or nonmetals,

00:03:15.830 --> 00:03:18.680
you can oftentimes
predict what type of bond

00:03:18.680 --> 00:03:20.220
is going to form.

00:03:20.220 --> 00:03:24.790
So for example, if I have
a bond between a metal,

00:03:24.790 --> 00:03:28.217
a metal and a nonmetal, and a nonmetal,

00:03:29.257 --> 00:03:32.475
what type of bond do you
think is going to form?

00:03:32.475 --> 00:03:34.502
Well when you bond between a net metal

00:03:34.502 --> 00:03:36.770
and a nonmetal, and we
saw an example of that

00:03:36.770 --> 00:03:38.550
in that first video on bonding,

00:03:38.550 --> 00:03:42.600
say a metal like sodium, and
then a nonmetal like chlorine,

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we saw that that chlorine
will swipe an electron,

00:03:45.900 --> 00:03:47.570
the sodium might lose one,

00:03:47.570 --> 00:03:52.000
then the chlorine atom
becomes a chloride anion,

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and then the sodium atom
becomes a sodium cation

00:03:56.060 --> 00:03:57.640
and then they become
attracted to each other

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and then you form an ionic bond.

00:03:59.990 --> 00:04:04.053
So this tends to form ionic bonds.

00:04:05.020 --> 00:04:09.987
Now what if you were to have
a nonmetal with a nonmetal?

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Nonmetal times two,

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so two nonmetals bind,

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bound, I'm having trouble saying it,

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two nonmetals bonding to each other.

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What do you think is going to happen?

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Well we saw as an example
in that first video

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where we say well what happens
if oxygen bonds to oxygen?

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Well we saw that was a covalent bond

00:04:31.760 --> 00:04:33.810
and that is generally the case

00:04:33.810 --> 00:04:38.080
when you have two nonmetals
form bonds, it is covalent.

00:04:38.080 --> 00:04:39.930
And then last but not least,

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and this might be the most
obvious one of them all,

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what do you think happens when you have

00:04:45.070 --> 00:04:47.983
two metals forming a bond?

00:04:49.110 --> 00:04:53.340
Well you can imagine that
will be a metallic bond

00:04:53.340 --> 00:04:55.830
where they contribute
electrons to this kind

00:04:55.830 --> 00:04:58.960
of sea of electrons and
that's what makes them

00:04:58.960 --> 00:05:01.930
conduct electricity so well and malleable.

00:05:01.930 --> 00:05:03.180
So I'll leave you there.

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There are exceptions to
everything I just talked about

00:05:05.660 --> 00:05:06.840
but generally speaking,

00:05:06.840 --> 00:05:08.650
these notions will serve you well,

00:05:08.650 --> 00:05:11.053
especially in an
introductory chemistry class.


Electron configurations of ions

WEBVTT
Kind: captions
Language: en

00:00:00.120 --> 00:00:01.160
- [Instructor] In many videos

00:00:01.160 --> 00:00:05.640
we have already talked
about electron configuration

00:00:05.640 --> 00:00:07.180
and now in this video

00:00:07.180 --> 00:00:09.730
we're going to extend that understanding

00:00:09.730 --> 00:00:13.820
by thinking about the electron
configuration of ions.

00:00:13.820 --> 00:00:17.270
These are going to be charged atoms.

00:00:17.270 --> 00:00:19.820
Let's just start looking at some examples.

00:00:19.820 --> 00:00:23.550
Let's say we are dealing with fluorine.

00:00:23.550 --> 00:00:26.630
Now, we know what a
neutral fluorine atom's

00:00:26.630 --> 00:00:28.600
electron configuration would be.

00:00:28.600 --> 00:00:30.680
In fact, if you want a
little bit of practice,

00:00:30.680 --> 00:00:31.610
try to pause this video

00:00:31.610 --> 00:00:33.640
and think about what is
the electron configuration

00:00:33.640 --> 00:00:37.393
of a neutral fluorine atom?

00:00:38.260 --> 00:00:40.290
All right, now let's work
through this together.

00:00:40.290 --> 00:00:43.510
A neutral fluorine atom
has nine electrons,

00:00:43.510 --> 00:00:45.950
and we could just use our
Periodic Table of Elements.

00:00:45.950 --> 00:00:49.010
So first, we're going to
have two electrons in 1s.

00:00:49.010 --> 00:00:51.640
So we'll have 1s two.

00:00:51.640 --> 00:00:54.480
And then we're going to
go to the second shell.

00:00:54.480 --> 00:00:56.670
So then we go to 2s two.

00:00:56.670 --> 00:01:00.200
So far we have filled in four electrons.

00:01:00.200 --> 00:01:04.340
And next we got to the 2p sub-shell.

00:01:04.340 --> 00:01:05.610
And we are going to have,

00:01:05.610 --> 00:01:07.640
we're talking about a neutral fluorine,

00:01:07.640 --> 00:01:12.300
we are going to have one two
three four five electrons

00:01:12.300 --> 00:01:14.030
in that 2p sub-shell.

00:01:14.030 --> 00:01:16.920
So it's 2p five.

00:01:16.920 --> 00:01:20.080
So if that's the electron
configuration for fluorine,

00:01:20.080 --> 00:01:22.050
what do you think the
electron configuration

00:01:22.050 --> 00:01:24.120
for fluoride would be?

00:01:24.120 --> 00:01:28.630
This is just the anion that
has one extra electron.

00:01:28.630 --> 00:01:31.160
It is a negatively charged ion.

00:01:31.160 --> 00:01:33.260
Pause this video and try to figure it out.

00:01:34.450 --> 00:01:38.750
Well, here you're now going
to have one extra electron.

00:01:38.750 --> 00:01:42.060
The fluorine has nabbed
an electron from someplace

00:01:42.060 --> 00:01:44.710
and so where will that extra electron go?

00:01:44.710 --> 00:01:48.330
Well our 2p sub-shell has
space for one more electron.

00:01:48.330 --> 00:01:50.140
So that's where it will go.

00:01:50.140 --> 00:01:52.120
So the fluoride anion is going to have

00:01:52.120 --> 00:01:57.120
an electron configuration
of 1s two, 2s two, 2p,

00:01:58.480 --> 00:02:02.638
now it's going to have an
extra electron here, 2p six.

00:02:02.638 --> 00:02:05.410
2p six.

00:02:05.410 --> 00:02:07.190
Now let's do another example.

00:02:07.190 --> 00:02:10.600
Let's say we wanted to figure
out the electron configuration

00:02:10.600 --> 00:02:14.150
of a part positively charged calcium ion.

00:02:14.150 --> 00:02:15.840
So calcium, let's make it two plus.

00:02:15.840 --> 00:02:18.063
It has a positive charge of two.

00:02:18.970 --> 00:02:20.740
You could do this as a neutral calcium

00:02:20.740 --> 00:02:23.210
that has lost two electrons.

00:02:23.210 --> 00:02:25.900
What would be its electron configuration?

00:02:25.900 --> 00:02:28.638
Pause this video and
try to figure that out.

00:02:28.638 --> 00:02:31.350
All right, well one way
to figure this out is

00:02:31.350 --> 00:02:33.610
first we could figure out
the electron configuration

00:02:33.610 --> 00:02:35.077
of a neutral calcium atom

00:02:39.440 --> 00:02:41.699
and then from that, we can take two

00:02:41.699 --> 00:02:45.460
of the highest energy electrons away.

00:02:45.460 --> 00:02:48.710
And so neutral calcium, you could view it,

00:02:48.710 --> 00:02:51.340
actually let's do it in
noble gas configuration.

00:02:51.340 --> 00:02:53.620
Neutral calcium, the noble gas that comes

00:02:53.620 --> 00:02:56.150
right before calcium is argon.

00:02:56.150 --> 00:02:59.440
So it's going to have the
electron configuration of argon

00:02:59.440 --> 00:03:02.540
and then we are going
to have two electrons

00:03:02.540 --> 00:03:03.650
for that fourth shell.

00:03:03.650 --> 00:03:06.880
It's going to fill in the 4s sub-shell.

00:03:06.880 --> 00:03:08.700
And so we're going to have argon

00:03:08.700 --> 00:03:12.830
and then we're going to have,
let me do this in a new color,

00:03:12.830 --> 00:03:16.370
let's call this 4s two.

00:03:16.370 --> 00:03:17.620
Now what do you think is going to happen

00:03:17.620 --> 00:03:20.650
if we were to lose two electrons?

00:03:20.650 --> 00:03:23.900
Well those two electrons
in that 4s sub-shell,

00:03:23.900 --> 00:03:25.940
in the fourth shell, are gonna go away.

00:03:25.940 --> 00:03:27.970
And so the electron configuration here

00:03:27.970 --> 00:03:30.590
for calcium with a positive two charge,

00:03:30.590 --> 00:03:33.170
this calcium cation, is going to be

00:03:33.170 --> 00:03:36.830
the electron configuration
of argon and no 4s two.

00:03:36.830 --> 00:03:37.770
So it's actually going to have

00:03:37.770 --> 00:03:42.380
the exact same electron
configuration as argon.

00:03:42.380 --> 00:03:44.850
So I will leave you there,
just a couple of examples.

00:03:44.850 --> 00:03:47.410
And I encourage you,
if you're in the mood,

00:03:47.410 --> 00:03:50.050
just pick any of these
atoms, any of these elements,

00:03:50.050 --> 00:03:51.040
and think about what would happen

00:03:51.040 --> 00:03:52.700
if they gained or lost an electron

00:03:52.700 --> 00:03:55.203
and what their electron
configurations might be.


Khan Stories: Jason Spyres

WEBVTT
Kind: captions
Language: en

00:00:02.420 --> 00:00:04.430
- My name's Jason Spires.

00:00:04.430 --> 00:00:07.950
It's nice to be able to
use that name because,

00:00:07.950 --> 00:00:10.260
for many years, the
only name that mattered

00:00:10.260 --> 00:00:15.260
in my life was Mr. K99397 'cause
that was my prison number.

00:00:18.070 --> 00:00:21.230
Unfortunately, at a very young age,

00:00:21.230 --> 00:00:24.290
I made a stupid decision to sell cannabis,

00:00:24.290 --> 00:00:26.500
and I ended up in prison,

00:00:26.500 --> 00:00:27.950
and I was never really the type

00:00:27.950 --> 00:00:29.500
that was real good at school.

00:00:29.500 --> 00:00:31.140
Like, I was smart,

00:00:31.140 --> 00:00:33.853
but I wouldn't sit around
and wouldn't focus.

00:00:34.800 --> 00:00:36.310
Not trying to make excuses,

00:00:36.310 --> 00:00:39.680
but my parents had drug addictions.

00:00:39.680 --> 00:00:42.150
I probably didn't have the best guidance,

00:00:42.150 --> 00:00:44.180
but I still knowingly made my own choices.

00:00:44.180 --> 00:00:48.570
So I own up to that, but
when I got to prison,

00:00:48.570 --> 00:00:51.290
I had moments in my life
that made me realize

00:00:51.290 --> 00:00:54.563
I had a distorted notion
of what success really was,

00:00:55.503 --> 00:00:57.200
and fortunately, when I got arrested,

00:00:57.200 --> 00:00:59.190
it helped my mother get clean and sober,

00:00:59.190 --> 00:01:01.760
and it helped my father
get clean and sober.

00:01:01.760 --> 00:01:04.170
So I now had parents that
were actively involved

00:01:04.170 --> 00:01:06.900
in trying to do good things for me,

00:01:06.900 --> 00:01:10.610
and I decided that I wanted
to improve my education,

00:01:10.610 --> 00:01:15.050
and one of the things that I remember is

00:01:15.050 --> 00:01:18.270
my mother went online to Khan Academy,

00:01:18.270 --> 00:01:20.420
and she would get printed out transcripts

00:01:20.420 --> 00:01:22.720
of what the videos were
talking about in math,

00:01:23.580 --> 00:01:26.753
and she'd send me the transcripts,
and I'd read over 'em,

00:01:27.650 --> 00:01:31.410
and from that, I started
realizing I understand

00:01:31.410 --> 00:01:32.500
how fractions work.

00:01:32.500 --> 00:01:34.730
I understand math on a deeper level.

00:01:34.730 --> 00:01:35.880
I was always good with it,

00:01:35.880 --> 00:01:36.960
but now I was getting to the point

00:01:36.960 --> 00:01:39.650
where I could actually
perform well with it.

00:01:39.650 --> 00:01:40.640
While I was in prison,

00:01:40.640 --> 00:01:44.350
I was able to, with Khan
Academy's transcripts,

00:01:44.350 --> 00:01:47.600
learn how to do many
of the math procedures

00:01:47.600 --> 00:01:50.250
that helped me perform better on the SAT,

00:01:50.250 --> 00:01:52.760
and when I got towards
the end of my sentence,

00:01:52.760 --> 00:01:55.140
I was able to get to a
work-release program,

00:01:55.140 --> 00:01:57.520
which allowed me to go
to community college,

00:01:57.520 --> 00:01:59.002
and I had to take the SAT

00:01:59.002 --> 00:02:02.610
in anticipation of
transferring to a university,

00:02:02.610 --> 00:02:06.550
and I used the Khan Academy SAT prep,

00:02:06.550 --> 00:02:10.790
and fortunately, I was
accepted as a transfer student

00:02:10.790 --> 00:02:12.273
at Stanford University,

00:02:13.210 --> 00:02:16.540
and little did I know that
a year later I would go

00:02:16.540 --> 00:02:21.540
to my classroom, and Mr. Khan
would be our guest speaker,

00:02:21.590 --> 00:02:24.980
and I got to tell him something

00:02:27.160 --> 00:02:28.780
that was very difficult to say

00:02:28.780 --> 00:02:31.470
but was the truest words I could think of,

00:02:31.470 --> 00:02:32.733
and that was thank you,

00:02:35.110 --> 00:02:39.100
and it's not just who he
is 'cause, like he said,

00:02:39.100 --> 00:02:40.970
he did nothing personally for me.

00:02:40.970 --> 00:02:42.840
It was his organization.

00:02:42.840 --> 00:02:46.460
It was having videos that
were easy to understand.

00:02:46.460 --> 00:02:49.320
It was being able to learn
knowledge without having to admit

00:02:49.320 --> 00:02:52.220
that I'm stupid because
I didn't already know it.

00:02:52.220 --> 00:02:54.130
It took away the embarrassment factor

00:02:54.130 --> 00:02:56.410
of having to ask someone else,

00:02:56.410 --> 00:03:01.040
and so if you're a part
of that organization,

00:03:01.040 --> 00:03:06.040
if you're a donor, if you're
Miss Door who gave Mr. Khan

00:03:07.800 --> 00:03:12.523
the impetus he needed to
make this actually happen,

00:03:14.100 --> 00:03:18.160
thank you because you played a role

00:03:18.160 --> 00:03:21.420
in me now being a Stanford
University student

00:03:21.420 --> 00:03:24.860
and studying computer science
after being locked up 15 years

00:03:24.860 --> 00:03:27.160
without access to technology.

00:03:27.160 --> 00:03:31.230
So I appreciate everything
that's been done

00:03:31.230 --> 00:03:32.980
for me in my life,

00:03:32.980 --> 00:03:35.300
and there's been so many people
that's contributed to it,

00:03:35.300 --> 00:03:38.010
but I can honestly say that Khan Academy

00:03:38.010 --> 00:03:40.530
and everyone involved
with the organization

00:03:40.530 --> 00:03:43.120
and everyone who has supported
its expansion and growth

00:03:43.120 --> 00:03:46.920
to other students has
made an impact upon me,

00:03:46.920 --> 00:03:51.370
and I can only tell you that
there's so many other people

00:03:52.690 --> 00:03:56.410
that have the potential
to make my story nothing

00:03:56.410 --> 00:03:59.130
if they can just get their hands

00:03:59.130 --> 00:04:03.700
on the ability to learn
the way that I was able to,

00:04:03.700 --> 00:04:05.513
which Khan Academy was a part of.


What to do the night before an exam: 3 tips from Sal Khan

WEBVTT
Kind: captions
Language: en

00:00:00.740 --> 00:00:03.102
- Here are my three
tips to reducing stress

00:00:03.102 --> 00:00:05.833
the night before a test.

00:00:05.833 --> 00:00:09.850
Tip one, stay physically healthy.

00:00:09.850 --> 00:00:11.211
There's a tendency that the night before

00:00:11.211 --> 00:00:12.650
you wanna cram,

00:00:12.650 --> 00:00:13.640
you wanna stay up late,

00:00:13.640 --> 00:00:14.860
you're stressed, you're anxious.

00:00:14.860 --> 00:00:16.620
That's the exact wrong thing to do.

00:00:16.620 --> 00:00:19.340
The night before you
have to get good rest.

00:00:19.340 --> 00:00:20.210
You have to relax,

00:00:20.210 --> 00:00:21.410
maybe meditate,

00:00:21.410 --> 00:00:23.851
watch a fun show, laugh a little bit,

00:00:23.851 --> 00:00:25.740
hang out with your family,

00:00:25.740 --> 00:00:27.690
and eat a healthy light meal.

00:00:27.690 --> 00:00:29.900
You don't wanna have stomach issues

00:00:29.900 --> 00:00:30.930
as you go into the test.

00:00:30.930 --> 00:00:34.986
Tip two, organize your logistics.

00:00:34.986 --> 00:00:36.670
It's really important that

00:00:36.670 --> 00:00:37.820
as you go into the test

00:00:37.820 --> 00:00:39.354
that you have to worry
about as little as possible.

00:00:39.354 --> 00:00:40.830
So the best way to do that

00:00:40.830 --> 00:00:42.640
is to organize everything ahead of time.

00:00:42.640 --> 00:00:43.930
Know where you're going.

00:00:43.930 --> 00:00:45.310
If you have to print out something,

00:00:45.310 --> 00:00:46.366
print it out ahead of time.

00:00:46.366 --> 00:00:48.240
Get your pencils in shape

00:00:48.240 --> 00:00:49.073
and sharpened.

00:00:49.073 --> 00:00:51.410
Even your clothes ready for the morning of

00:00:51.410 --> 00:00:52.243
so that you just have to

00:00:52.243 --> 00:00:55.940
have nice night of sleep,
wake up, do some simple tasks

00:00:55.940 --> 00:00:58.140
and then go to the test.

00:00:58.140 --> 00:00:59.558
The less you have to worry
about that morning the better.

00:00:59.558 --> 00:01:04.451
Tip three, stay positive and confident.

00:01:04.451 --> 00:01:05.798
And perhaps the most important thing

00:01:05.798 --> 00:01:07.367
is as you go to the test itself,

00:01:07.367 --> 00:01:10.137
keep a relaxed and positive attitude.

00:01:10.137 --> 00:01:11.758
If you're stressed, if you're anxious,

00:01:11.758 --> 00:01:13.581
that's going to become a
self-fulfilling prophecy.

00:01:13.581 --> 00:01:17.248
So take a deep breath, breathe out slowly,

00:01:17.248 --> 00:01:19.193
and say I got this.


Ionic bonds

WEBVTT
Kind: captions
Language: en

00:00:00.120 --> 00:00:01.840
- [Instructor] Most of what
we've talked about so far

00:00:01.840 --> 00:00:04.260
has been atoms in isolation.

00:00:04.260 --> 00:00:05.880
We have thought about the number

00:00:05.880 --> 00:00:08.260
of electrons and protons and neutrons

00:00:08.260 --> 00:00:10.980
and the electron configuration of atoms.

00:00:10.980 --> 00:00:14.160
But atoms don't just operate in isolation.

00:00:14.160 --> 00:00:16.710
If that were the case, the
whole universe including us

00:00:16.710 --> 00:00:19.400
would just be a bunch of
atoms drifting around.

00:00:19.400 --> 00:00:21.050
What begins to be interesting is

00:00:21.050 --> 00:00:24.300
how the atoms actually
interact with each other.

00:00:24.300 --> 00:00:27.910
And one of the most interesting
forms of interaction is

00:00:27.910 --> 00:00:31.760
when they stick to each other
in some way shape or form.

00:00:31.760 --> 00:00:35.240
And this sticking together of atoms is

00:00:35.240 --> 00:00:38.060
what we are going to study in this video.

00:00:38.060 --> 00:00:42.770
Another way to talk about
it is, how do atoms bond?

00:00:42.770 --> 00:00:46.370
Now as we will see, there
are several types of bonds

00:00:46.370 --> 00:00:47.690
and it's really a spectrum.

00:00:47.690 --> 00:00:49.480
But let's just start with
what I would consider

00:00:49.480 --> 00:00:51.940
one of the more extreme type of bonds.

00:00:51.940 --> 00:00:54.660
And to understand it, let's get
a periodic table of elements

00:00:54.660 --> 00:00:56.350
out right over here.

00:00:56.350 --> 00:01:00.950
So let's say that we are dealing
with a group one element.

00:01:00.950 --> 00:01:03.860
Let's say sodium right over here.

00:01:03.860 --> 00:01:06.290
What's interesting about
group one elements is

00:01:06.290 --> 00:01:09.080
that they have one valence electron.

00:01:09.080 --> 00:01:12.040
If we want to visualize
the valence electrons

00:01:12.040 --> 00:01:14.490
for, say, sodium we could do it

00:01:14.490 --> 00:01:17.110
with what's known as a Lewis dot structure

00:01:17.110 --> 00:01:19.220
or a Lewis electron dot structure,

00:01:19.220 --> 00:01:22.150
sometimes just called a
dot structure for short.

00:01:22.150 --> 00:01:25.740
But because a neutral sodium
has one valence electron,

00:01:25.740 --> 00:01:30.690
we would just draw that one
valence electron like that.

00:01:30.690 --> 00:01:33.360
Now let's go to the other
end of the periodic table

00:01:33.360 --> 00:01:35.530
and say, look at chlorine.

00:01:35.530 --> 00:01:37.490
Chlorine is a halogen.

00:01:37.490 --> 00:01:41.380
Halogens have seven valence electrons

00:01:41.380 --> 00:01:44.970
so chlorine's valence
electrons would look like this.

00:01:44.970 --> 00:01:49.970
It has one two three four five
six seven valence electrons.

00:01:54.800 --> 00:01:57.670
And so you could imagine
chlorine would love

00:01:57.670 --> 00:01:58.880
to get another electron

00:01:58.880 --> 00:02:01.240
in order to complete its outer shell.

00:02:01.240 --> 00:02:04.300
And we've also studied in
other videos these atoms,

00:02:04.300 --> 00:02:06.850
these elements at the top
right of the periodic table

00:02:06.850 --> 00:02:08.650
which are not the noble gases,

00:02:08.650 --> 00:02:11.260
but especially the top of these halogens,

00:02:11.260 --> 00:02:13.170
things like oxygen, nitrogen.

00:02:13.170 --> 00:02:14.830
These are very electronegative.

00:02:14.830 --> 00:02:18.610
They like to pull
electrons, hog electrons.

00:02:18.610 --> 00:02:20.100
And so what do you
think is going to happen

00:02:20.100 --> 00:02:22.720
when you put these characters together?

00:02:22.720 --> 00:02:25.010
This guy wants to lose the electrons

00:02:25.010 --> 00:02:28.300
and chlorine wants to gain an electron.

00:02:28.300 --> 00:02:30.980
Well, maybe the chlorine
will take an electron

00:02:30.980 --> 00:02:31.940
from the sodium.

00:02:31.940 --> 00:02:33.320
On a real chemical reaction,

00:02:33.320 --> 00:02:34.880
you would have trillions of these

00:02:34.880 --> 00:02:36.170
and they're bouncing around

00:02:36.170 --> 00:02:37.800
and different things are happening

00:02:37.800 --> 00:02:38.740
but just for simplicity,

00:02:38.740 --> 00:02:40.800
let's just imagine that
these are the only two.

00:02:40.800 --> 00:02:43.330
And let's imagine that
this chlorine is able

00:02:43.330 --> 00:02:46.810
to nab an electron from this sodium.

00:02:46.810 --> 00:02:48.980
So what is going to happen?

00:02:48.980 --> 00:02:53.980
This sodium is then going to
become positively charged,

00:02:54.160 --> 00:02:56.400
'cause it's going to lose an electron.

00:02:56.400 --> 00:03:00.340
And then the chlorine,
the chlorine is now going

00:03:00.340 --> 00:03:02.040
to gain an electron.

00:03:02.040 --> 00:03:04.663
So it's going to become a chloride anion.

00:03:04.663 --> 00:03:06.510
Anion is a negative ion.

00:03:06.510 --> 00:03:09.260
It's a sodium cation, a positive ion.

00:03:09.260 --> 00:03:10.560
Ion means it's charged.

00:03:10.560 --> 00:03:13.290
And now it's a chloride anion.

00:03:13.290 --> 00:03:15.430
So it has the valence
electrons that it had before

00:03:15.430 --> 00:03:16.800
and then you could imagine

00:03:16.800 --> 00:03:18.980
that it gains one from the sodium.

00:03:18.980 --> 00:03:22.780
And now it has a negative charge.

00:03:22.780 --> 00:03:25.730
Now what do we know about
positively charged ions

00:03:25.730 --> 00:03:27.780
and negatively charged ions?

00:03:27.780 --> 00:03:29.490
Opposites attract.

00:03:29.490 --> 00:03:30.410
Coulomb forces.

00:03:30.410 --> 00:03:31.930
So these two characters are going

00:03:31.930 --> 00:03:33.810
to be attracted to each other,

00:03:33.810 --> 00:03:34.810
or another way to think of it,

00:03:34.810 --> 00:03:35.780
they're gonna stick together,

00:03:35.780 --> 00:03:37.250
or another way you could think about it,

00:03:37.250 --> 00:03:39.440
they are going to be bonded.

00:03:39.440 --> 00:03:44.440
And they will form a
compound of sodium chloride.

00:03:45.300 --> 00:03:49.380
And notice the whole
compound here is neutral.

00:03:49.380 --> 00:03:51.820
It has a plus one charge for the sodium,

00:03:51.820 --> 00:03:53.680
a negative one charge for the chloride,

00:03:53.680 --> 00:03:55.290
but taken together it is neutral

00:03:55.290 --> 00:03:57.523
because these are hanging out together.

00:03:58.410 --> 00:04:01.470
And this type of bond between ions,

00:04:01.470 --> 00:04:03.670
you might guess what it's called.

00:04:03.670 --> 00:04:06.490
It is called an ionic bond.

00:04:06.490 --> 00:04:08.963
Ionic bond.


Covalent bonds

WEBVTT
Kind: captions
Language: en

00:00:00.350 --> 00:00:01.480
- [Instructor] In a previous video,

00:00:01.480 --> 00:00:04.200
we introduced ourselves
to the idea of bonds

00:00:04.200 --> 00:00:06.330
and the idea of ionic bonds,

00:00:06.330 --> 00:00:08.730
where one atom essentially is able

00:00:08.730 --> 00:00:11.380
to take electrons from another atom.

00:00:11.380 --> 00:00:13.620
But then because one
becomes positively charged

00:00:13.620 --> 00:00:15.220
and the other becomes negatively charged,

00:00:15.220 --> 00:00:16.910
they get attracted to each other.

00:00:16.910 --> 00:00:18.720
Now we're going to go to the other end

00:00:18.720 --> 00:00:20.060
of the bonding spectrum,

00:00:20.060 --> 00:00:22.610
where instead of stealing
electrons from each other,

00:00:22.610 --> 00:00:24.430
we're going to share them.

00:00:24.430 --> 00:00:27.690
Let's say we're dealing
with two oxygen atoms.

00:00:27.690 --> 00:00:30.380
So let me draw one oxygen here.

00:00:30.380 --> 00:00:33.060
A neutral oxygen has
eight electrons total,

00:00:33.060 --> 00:00:34.910
but six of them are in its outer shell.

00:00:34.910 --> 00:00:37.420
So it has one,

00:00:37.420 --> 00:00:39.320
two, three,

00:00:39.320 --> 00:00:41.800
four, five,

00:00:41.800 --> 00:00:44.260
six valence electrons.

00:00:44.260 --> 00:00:48.510
And the way that I arrange
them is I pair them up last.

00:00:48.510 --> 00:00:50.810
So you have these two valence electrons

00:00:50.810 --> 00:00:53.000
that are not paired with another electron.

00:00:53.000 --> 00:00:54.770
And now let me draw another oxygen,

00:00:54.770 --> 00:00:56.730
and I'm going do it
with a different color,

00:00:56.730 --> 00:01:00.520
so we can keep track of the electrons.

00:01:00.520 --> 00:01:01.920
So another oxygen right over there,

00:01:01.920 --> 00:01:06.440
also has six valence
electrons, one, two, three,

00:01:06.440 --> 00:01:11.440
four, five, six valence electrons.

00:01:11.920 --> 00:01:13.870
Now this oxygen on the left,

00:01:13.870 --> 00:01:15.690
in order to become more stable,

00:01:15.690 --> 00:01:17.740
it would love to somehow gain

00:01:17.740 --> 00:01:19.960
or maybe share two more electrons.

00:01:19.960 --> 00:01:22.830
And of course, this oxygen on
the right, it's still oxygen.

00:01:22.830 --> 00:01:24.400
It also would love to gain

00:01:24.400 --> 00:01:27.810
or share two more valence electrons.

00:01:27.810 --> 00:01:29.280
So how could it do it?

00:01:29.280 --> 00:01:33.390
Well, what if the oxygen on
the left shared this electron

00:01:33.390 --> 00:01:35.600
and this electron with
the oxygen on the right,

00:01:35.600 --> 00:01:38.070
and the oxygen on the
right shared this electron

00:01:38.070 --> 00:01:41.380
and this electron with
the oxygen on the left?

00:01:41.380 --> 00:01:43.020
Well, if they did that,

00:01:43.020 --> 00:01:45.340
you would have something
that looks like this.

00:01:45.340 --> 00:01:47.240
You have your oxygen on the left.

00:01:47.240 --> 00:01:50.950
You have the oxygen on the right.

00:01:50.950 --> 00:01:54.750
And the way we show two
electrons that are being shared,

00:01:54.750 --> 00:01:57.590
let's say these two
electrons are being shared,

00:01:57.590 --> 00:02:00.310
is just a line like this.

00:02:00.310 --> 00:02:01.960
This shows that there are two electrons

00:02:01.960 --> 00:02:04.670
that are being shared
by these two oxygens.

00:02:04.670 --> 00:02:07.330
And let's say that these two electrons

00:02:07.330 --> 00:02:09.290
are also being shared.

00:02:09.290 --> 00:02:11.190
You would do that with a line like this.

00:02:11.190 --> 00:02:12.600
And then we could draw the remainder

00:02:12.600 --> 00:02:13.650
of the valence electrons.

00:02:13.650 --> 00:02:15.600
This oxygen on the left had,

00:02:15.600 --> 00:02:17.670
outside of the electrons
that are being shared,

00:02:17.670 --> 00:02:20.573
it had four more valence electrons.

00:02:21.870 --> 00:02:23.680
And then the oxygen on the right

00:02:23.680 --> 00:02:25.900
had four more valence electrons,

00:02:25.900 --> 00:02:28.630
one, two, three, four.

00:02:28.630 --> 00:02:31.340
Now what's interesting here
is the shared electrons,

00:02:31.340 --> 00:02:35.580
these are going to cause these
oxygens to stick together.

00:02:35.580 --> 00:02:36.560
If they don't stick together,

00:02:36.560 --> 00:02:38.770
these electrons aren't going to be shared.

00:02:38.770 --> 00:02:43.220
So what we have formed here
is known as a covalent bond,

00:02:43.220 --> 00:02:46.130
covalent bond.

00:02:46.130 --> 00:02:49.820
And what's interesting is it
allows both of these oxygens

00:02:49.820 --> 00:02:52.130
in some ways to be more stable.

00:02:52.130 --> 00:02:54.390
From the left oxygen's point of view,

00:02:54.390 --> 00:02:56.350
it had six valence electrons,

00:02:56.350 --> 00:02:58.880
but now it's able to share two more.

00:02:58.880 --> 00:03:00.720
Remember, each of these bonds,

00:03:00.720 --> 00:03:03.390
each of these lines
represent two electrons.

00:03:03.390 --> 00:03:05.090
So this oxygen could say, hey,

00:03:05.090 --> 00:03:07.850
I get to have one, two, three, four,

00:03:07.850 --> 00:03:10.880
six, eight electrons
that I'm dealing with,

00:03:10.880 --> 00:03:12.530
and the same thing is going to be true

00:03:12.530 --> 00:03:15.280
of this oxygen on the right.

00:03:15.280 --> 00:03:16.780
Now there are some covalent bonds

00:03:16.780 --> 00:03:19.090
that are between not-so-equals.

00:03:19.090 --> 00:03:22.630
So for example, if we're
talking about water

00:03:22.630 --> 00:03:25.800
and if we're talking about how
oxygen bonds with hydrogen.

00:03:25.800 --> 00:03:28.100
So if we have oxygen right over here,

00:03:28.100 --> 00:03:31.890
once again, I can draw its six
valence electrons, one, two,

00:03:31.890 --> 00:03:35.050
three, four, five,

00:03:35.050 --> 00:03:38.400
and let me just draw the
sixth one right over there.

00:03:38.400 --> 00:03:40.140
And if I have hydrogen,

00:03:40.140 --> 00:03:42.880
hydrogen has one valence electron.

00:03:42.880 --> 00:03:44.630
So let's say that's a
hydrogen right over there

00:03:44.630 --> 00:03:45.820
with one valence electron,

00:03:45.820 --> 00:03:47.610
maybe another hydrogen right over there

00:03:47.610 --> 00:03:49.600
with one valence electron.

00:03:49.600 --> 00:03:51.950
Oxygen and hydrogen form covalent bonds.

00:03:51.950 --> 00:03:54.610
In fact, that is how water is formed.

00:03:54.610 --> 00:03:56.650
And so what would that look like?

00:03:56.650 --> 00:03:57.880
Well, it would look like this.

00:03:57.880 --> 00:03:59.720
You have oxygen right over here.

00:03:59.720 --> 00:04:03.540
You have these two pairs of
electrons that I keep drawing.

00:04:03.540 --> 00:04:06.560
And then this electron right over here

00:04:06.560 --> 00:04:08.810
could be shared with the hydrogen,

00:04:08.810 --> 00:04:10.270
and that hydrogen's
electron could be shared

00:04:10.270 --> 00:04:11.260
with the oxygen.

00:04:11.260 --> 00:04:15.100
So that forms a covalent
bond with this hydrogen.

00:04:15.100 --> 00:04:17.170
And then this electron

00:04:17.170 --> 00:04:19.630
from the oxygen can be
shared with the hydrogen,

00:04:19.630 --> 00:04:21.100
and that electron from
the hydrogen can be shared

00:04:21.100 --> 00:04:21.940
with the oxygen.

00:04:21.940 --> 00:04:24.400
And so that would form a covalent bond

00:04:24.400 --> 00:04:26.003
with that other hydrogen.

00:04:27.720 --> 00:04:31.200
And now here, once again,
oxygen can kinda pretend

00:04:31.200 --> 00:04:33.370
like it has eight valence electrons,

00:04:33.370 --> 00:04:35.930
two, four, six, eight.

00:04:35.930 --> 00:04:37.980
And the hydrogens can kind of pretend

00:04:37.980 --> 00:04:39.910
that it has two valence electrons.

00:04:39.910 --> 00:04:42.370
But the one difference here is that oxygen

00:04:42.370 --> 00:04:45.280
is a lot more electronegative
than hydrogen.

00:04:45.280 --> 00:04:46.960
It's to the right of hydrogen.

00:04:46.960 --> 00:04:49.590
It's in this top-right corner, outside of,

00:04:49.590 --> 00:04:51.060
other than the noble gases,

00:04:51.060 --> 00:04:53.290
that really like to hog electrons.

00:04:53.290 --> 00:04:55.370
So what do you think is
going to happen here?

00:04:55.370 --> 00:04:58.120
Well, the electrons in each
of these covalent bonds

00:04:58.120 --> 00:05:00.280
are going to hang out around the oxygen

00:05:00.280 --> 00:05:02.420
more often than around the hydrogen.

00:05:02.420 --> 00:05:04.560
So if the electrons spend
more time around the oxygen,

00:05:04.560 --> 00:05:05.700
you're going to have, in general,

00:05:05.700 --> 00:05:08.020
more negative charge around the oxygen.

00:05:08.020 --> 00:05:11.840
And so you're going to have
a partial negative charge

00:05:11.840 --> 00:05:14.860
on the oxygen end of the water molecule,

00:05:14.860 --> 00:05:17.440
and then you're going to
have partial positive charges

00:05:17.440 --> 00:05:20.750
on the hydrogen ends of the molecules.

00:05:20.750 --> 00:05:21.610
And in case you're curious,

00:05:21.610 --> 00:05:23.320
that little symbol I'm using for partial,

00:05:23.320 --> 00:05:25.980
that's the lowercase Greek letter delta,

00:05:25.980 --> 00:05:27.820
which is just the convention in chemistry.

00:05:27.820 --> 00:05:30.690
And so this type of covalent bond,

00:05:30.690 --> 00:05:32.550
because there is some polarity,

00:05:32.550 --> 00:05:35.240
one side has more charge than the other,

00:05:35.240 --> 00:05:38.390
this is known as a polar covalent bond,

00:05:38.390 --> 00:05:41.933
polar covalent bond.


Metallic bonds

WEBVTT
Kind: captions
Language: en

00:00:00.240 --> 00:00:01.860
- [Instructor] Now the last type of bond

00:00:01.860 --> 00:00:06.860
I'm going to talk about is
known as the metallic bond,

00:00:07.040 --> 00:00:08.810
which I think I know a little bit about

00:00:08.810 --> 00:00:10.400
because I was the lead singer

00:00:10.400 --> 00:00:12.730
of a metallic bond in high school.

00:00:12.730 --> 00:00:15.540
I'll talk about that in future videos.

00:00:15.540 --> 00:00:20.070
But let's just take one of
our metallic atoms here.

00:00:20.070 --> 00:00:21.740
Iron is a good example.

00:00:21.740 --> 00:00:25.823
Iron is maybe one of the
most referred to metals.

00:00:26.950 --> 00:00:29.430
Let's say we have a bunch of iron atoms.

00:00:29.430 --> 00:00:33.333
So Fe, Fe, Fe, Fe, hope you can read that.

00:00:36.930 --> 00:00:38.150
These are all iron atoms.

00:00:38.150 --> 00:00:39.990
And if they're just atoms by themselves

00:00:39.990 --> 00:00:41.350
they're going to be neutral.

00:00:41.350 --> 00:00:44.340
But when they are mushed together,

00:00:44.340 --> 00:00:46.330
they will form a metallic bond.

00:00:46.330 --> 00:00:47.930
Makes sense because they're metals.

00:00:47.930 --> 00:00:50.100
And what's interesting
about metallic bonds,

00:00:50.100 --> 00:00:51.510
I'll draw it down here, is

00:00:51.510 --> 00:00:54.940
that metals like to share their electrons

00:00:54.940 --> 00:00:56.330
with the other metals.

00:00:56.330 --> 00:00:58.860
It kinda forms this sea of electrons.

00:00:58.860 --> 00:01:01.250
So what it can look like is,

00:01:01.250 --> 00:01:03.450
each of the irons lose an electron,

00:01:03.450 --> 00:01:04.460
I'll draw it a little bit bigger.

00:01:04.460 --> 00:01:08.473
So let's say this is Fe plus,
so it has a positive charge.

00:01:09.580 --> 00:01:12.521
Fe plus has a positive charge.

00:01:12.521 --> 00:01:16.544
Fe plus, these are all
iron ions, you can imagine.

00:01:16.544 --> 00:01:19.010
Fe plus, and we're imagining

00:01:19.010 --> 00:01:20.300
that they have this positive charge

00:01:20.300 --> 00:01:22.340
because they've all
contributed an electron

00:01:22.340 --> 00:01:24.570
to this sea of electrons.

00:01:24.570 --> 00:01:27.260
So you have an electron here
which has a negative charge.

00:01:27.260 --> 00:01:29.260
And electrons are not this big,

00:01:29.260 --> 00:01:31.130
but this is just so that you can see it.

00:01:31.130 --> 00:01:33.630
Electron here that has a negative charge.

00:01:33.630 --> 00:01:37.930
And so you can imagine these
positive ions are attracted

00:01:37.930 --> 00:01:42.640
to the sea of negativity, the
sea of negative electrons.

00:01:42.640 --> 00:01:44.020
Another way to think about it is,

00:01:44.020 --> 00:01:48.110
is that metals, when they
bond in metallic bonds,

00:01:48.110 --> 00:01:50.420
they will have overlapping
valence electrons.

00:01:50.420 --> 00:01:52.540
And those valence electrons are not fixed

00:01:52.540 --> 00:01:56.010
to just one of the atoms,
they can move around.

00:01:56.010 --> 00:01:58.740
And this is what gives metals
many of the characteristics

00:01:58.740 --> 00:02:00.460
we associate with metals.

00:02:00.460 --> 00:02:01.580
It conducts electricity

00:02:01.580 --> 00:02:05.390
because these electrons can
move around quite easily.

00:02:05.390 --> 00:02:08.100
It makes them malleable,
you can bend it easily.

00:02:08.100 --> 00:02:09.980
You can imagine these iron ions

00:02:09.980 --> 00:02:13.090
in this pudding, or this sea of electrons.

00:02:13.090 --> 00:02:15.040
So you can bend it, it doesn't break.

00:02:15.040 --> 00:02:18.300
Well if you were to take a
bar of a salt right over here,

00:02:18.300 --> 00:02:20.650
if you were to try to
bend it, it's very rigid.

00:02:20.650 --> 00:02:23.130
It is going to break.

00:02:23.130 --> 00:02:25.740
So there we have it, the types of bonds.

00:02:25.740 --> 00:02:27.550
It's important to realize
that you can view it

00:02:27.550 --> 00:02:28.700
as something of a spectrum.

00:02:28.700 --> 00:02:31.360
At one end, you have
things like ionic bonds

00:02:31.360 --> 00:02:33.420
where one character swipes an electron

00:02:33.420 --> 00:02:34.367
from another character and says,

00:02:34.367 --> 00:02:36.600
"Hey, but now we're
attracted to each other,"

00:02:36.600 --> 00:02:39.070
and you get something like salt.

00:02:39.070 --> 00:02:40.930
Or you have covalent bonds

00:02:40.930 --> 00:02:43.470
where we outright share electrons.

00:02:43.470 --> 00:02:45.580
And then you have things
in between covalent bonds

00:02:45.580 --> 00:02:49.080
and ionic bonds where the
sharing is not so equal

00:02:49.080 --> 00:02:50.800
and you get polar covalent bonds.

00:02:50.800 --> 00:02:52.810
And then another form,
I guess you could say,

00:02:52.810 --> 00:02:55.770
of extreme sharing is the metallic bonds

00:02:55.770 --> 00:02:59.343
where you just have this
communal sea of electrons.


Isotopes

WEBVTT
Kind: captions
Language: en

00:00:00.250 --> 00:00:01.610
- [Instructor] In other
videos we have talked

00:00:01.610 --> 00:00:03.850
about that the type of
element that we are dealing

00:00:03.850 --> 00:00:06.270
with is defined by the number of protons

00:00:06.270 --> 00:00:07.970
in an atom's nucleus.

00:00:07.970 --> 00:00:11.080
So for example, any atom
with exactly one proton

00:00:11.080 --> 00:00:14.350
in its nucleus is by definition hydrogen.

00:00:14.350 --> 00:00:17.040
Any atom with six protons in its nucleus

00:00:17.040 --> 00:00:19.320
is by definition carbon,

00:00:19.320 --> 00:00:22.720
any atom with 17 protons in its nucleus

00:00:22.720 --> 00:00:25.200
is by definition chlorine,

00:00:25.200 --> 00:00:27.960
and so these numbers that I'm
circling on a periodic table

00:00:27.960 --> 00:00:30.750
of elements, that's known
as the atomic number,

00:00:30.750 --> 00:00:34.540
but it's really just the
number of protons in an atom

00:00:34.540 --> 00:00:36.630
of that element types nucleus.

00:00:36.630 --> 00:00:40.660
And that defines what
type of element it is.

00:00:40.660 --> 00:00:42.880
But in this video we're going
to dig a little bit deeper

00:00:42.880 --> 00:00:46.260
and realize that you can
still have different versions

00:00:46.260 --> 00:00:51.260
of the same element and these
versions in chemistry speak

00:00:51.490 --> 00:00:54.150
are known as isotopes.

00:00:54.150 --> 00:00:57.480
Now how can you have different
versions of the same element

00:00:57.480 --> 00:01:01.180
if the number of protons
defines what the element is?

00:01:01.180 --> 00:01:04.510
Well, the versions the various
isotopes are going to happen

00:01:04.510 --> 00:01:07.490
based on the number of neutrons you have.

00:01:07.490 --> 00:01:12.490
So for example, there are two
stable isotopes of chlorine,

00:01:13.200 --> 00:01:17.520
there's one version of
chlorine known as chlorine 35.

00:01:17.520 --> 00:01:20.360
Let me write it over here, chlorine 35.

00:01:20.360 --> 00:01:21.970
It's sometimes written like this,

00:01:21.970 --> 00:01:25.880
in fact it's often written
like this, chlorine 35

00:01:25.880 --> 00:01:29.560
and this isotope notation
that you see over here

00:01:29.560 --> 00:01:31.640
where we have 35 in the top left,

00:01:31.640 --> 00:01:35.100
that 35 is the sum of this version,

00:01:35.100 --> 00:01:39.600
this isotope of chlorines
protons and neutrons.

00:01:39.600 --> 00:01:44.550
This number 35 is this isotope
of chlorines mass number.

00:01:44.550 --> 00:01:47.610
So it has a total of 35
protons and neutrons,

00:01:47.610 --> 00:01:50.663
how many neutrons does this
version of chlorine have?

00:01:51.900 --> 00:01:54.510
Well it's going to have 17 protons.

00:01:54.510 --> 00:01:57.250
17 protons, I know that
because we are dealing

00:01:57.250 --> 00:02:00.130
with chlorine, so how many
neutrons will it have?

00:02:00.130 --> 00:02:05.130
Well 35 minus 17 is 18, 18 neutrons.

00:02:06.860 --> 00:02:10.920
And there's another version
of chlorine that is stable

00:02:10.920 --> 00:02:14.610
and that is chlorine 37.

00:02:14.610 --> 00:02:17.250
Now how many protons
is that going to have?

00:02:17.250 --> 00:02:18.250
Well that's a trick question,

00:02:18.250 --> 00:02:21.530
by definition it's chlorine,
it's going to have 17 protons.

00:02:21.530 --> 00:02:24.500
This is going to have 17 protons,

00:02:24.500 --> 00:02:26.620
but then how many neutrons will it have?

00:02:26.620 --> 00:02:29.340
Well the protons plus the neutrons is 37,

00:02:29.340 --> 00:02:32.850
so 17 plus 20 is going to be 37.

00:02:32.850 --> 00:02:36.510
So it's going to be 20 neutrons,

00:02:36.510 --> 00:02:41.103
and this would be written
out as chlorine, chlorine 37.

00:02:42.280 --> 00:02:45.700
So you can see these are two
different versions of chlorine,

00:02:45.700 --> 00:02:48.920
same number of protons
which make them chlorine,

00:02:48.920 --> 00:02:51.820
but different number of neutrons.

00:02:51.820 --> 00:02:54.240
Now you can imagine these
different versions are going

00:02:54.240 --> 00:02:56.940
to have different atomic masses,

00:02:56.940 --> 00:03:00.100
but here on a periodic table
of elements there's only one

00:03:00.100 --> 00:03:01.770
average atomic mass listed,

00:03:01.770 --> 00:03:05.670
and the key word here is this
is an average atomic mass.

00:03:05.670 --> 00:03:10.510
It's the weighted average of
the masses of the chlorines,

00:03:10.510 --> 00:03:13.180
the stable chlorines that you will find.

00:03:13.180 --> 00:03:18.180
So for example, in nature
75.77% of the chlorine

00:03:21.810 --> 00:03:25.070
found is chlorine 35,

00:03:25.070 --> 00:03:30.070
and then the remaining
24.23% of the chlorine found

00:03:31.520 --> 00:03:33.870
is chlorine 37.

00:03:33.870 --> 00:03:36.970
So when they calculate
this average atomic mass,

00:03:36.970 --> 00:03:39.610
what they do is they would
take, or you would take,

00:03:39.610 --> 00:03:44.610
if you're calculating it,
so this would be 75.77%

00:03:47.410 --> 00:03:50.485
times the atomic mass,

00:03:50.485 --> 00:03:55.485
atomic mass of chlorine 35 plus,

00:03:59.520 --> 00:04:04.520
and now the weight here would be 24.23%

00:04:04.720 --> 00:04:09.720
times the atomic mass,
atomic mass of chlorine 37.

00:04:14.910 --> 00:04:17.090
And if you were to do this
calculation you would get

00:04:17.090 --> 00:04:20.310
this number right over here, 35.45 unified

00:04:20.310 --> 00:04:22.080
atomic mass units.

00:04:22.080 --> 00:04:25.440
Now, how do you figure out the
atomic mass of chlorine 35?

00:04:25.440 --> 00:04:28.040
You might be tempted to
say it's just 35 unified

00:04:28.040 --> 00:04:30.740
atomic mass units, and you would be close

00:04:30.740 --> 00:04:34.900
because the mass of a
proton is close to one

00:04:34.900 --> 00:04:36.400
universal atomic mass unit,

00:04:36.400 --> 00:04:39.010
and the mass of a neutron is close to one

00:04:39.010 --> 00:04:40.480
universal atomic mass unit,

00:04:40.480 --> 00:04:42.670
and then the electrons
are have a much, much,

00:04:42.670 --> 00:04:44.020
much smaller mass.

00:04:44.020 --> 00:04:46.170
You can also almost
consider them negligible

00:04:46.170 --> 00:04:48.450
for atomic mass purposes,

00:04:48.450 --> 00:04:51.780
and so you will get an
atomic mass close to 35.

00:04:51.780 --> 00:04:53.870
But it actually turns out
it's a little bit different

00:04:53.870 --> 00:04:57.140
because not only are the masses
of each individual proton

00:04:57.140 --> 00:05:01.060
or neutron a little bit more
actually than one unified

00:05:01.060 --> 00:05:02.400
atomic mass unit,

00:05:02.400 --> 00:05:05.230
but when you put all those
protons and neutrons together

00:05:05.230 --> 00:05:08.810
in a nucleus, their
combined masses is actually

00:05:08.810 --> 00:05:12.260
a little bit less than
their individual masses

00:05:12.260 --> 00:05:13.500
if you were to just add them up,

00:05:13.500 --> 00:05:15.610
and that's actually
known as a mass defect.

00:05:15.610 --> 00:05:17.820
And so if you actually want
to know the atomic mass

00:05:17.820 --> 00:05:21.610
of chlorine 35, you can look
that up in a lot of tables,

00:05:21.610 --> 00:05:24.420
and you will see that it's
actually slightly under

00:05:24.420 --> 00:05:27.053
35 unified atomic mass units.


Mass spectrometry

WEBVTT
Kind: captions
Language: en

00:00:00.370 --> 00:00:01.320
- [Instructor] In other videos,

00:00:01.320 --> 00:00:03.860
we have talked about the idea that,

00:00:03.860 --> 00:00:05.210
even for a given element,

00:00:05.210 --> 00:00:07.540
you might have different
versions of that element,

00:00:07.540 --> 00:00:09.890
and we call those different
versions isotopes.

00:00:09.890 --> 00:00:12.020
And each isotope of an element

00:00:12.020 --> 00:00:14.450
can have a different atomic mass.

00:00:14.450 --> 00:00:17.570
And that stems from the idea
that, if it's a given element,

00:00:17.570 --> 00:00:19.490
it's going to have the
same number of protons,

00:00:19.490 --> 00:00:22.360
but you could have a
different number of neutrons.

00:00:22.360 --> 00:00:25.330
Now one question that you might
have been asking yourself is

00:00:25.330 --> 00:00:28.260
how have chemists been able to figure out

00:00:28.260 --> 00:00:31.030
what the various isotopes
of an element are

00:00:31.030 --> 00:00:32.820
and their relative abundance?

00:00:32.820 --> 00:00:34.710
What percentage of an element that we find

00:00:34.710 --> 00:00:37.920
in the universe is of isotope A

00:00:37.920 --> 00:00:40.070
versus, say, isotope B?

00:00:40.070 --> 00:00:42.330
And the answer to your question is

00:00:42.330 --> 00:00:46.300
they use a technique known
as mass spectrometry.

00:00:46.300 --> 00:00:50.190
I can never say it
right, mass spectrometry.

00:00:50.190 --> 00:00:52.960
Sometimes you'll hear the
word mass spectroscopy,

00:00:52.960 --> 00:00:55.980
and they're essentially
referring to the same idea.

00:00:55.980 --> 00:00:58.440
And what this technique is,

00:00:58.440 --> 00:01:01.630
is that you put a little bit
of a sample right over here,

00:01:01.630 --> 00:01:04.870
let's say we're talking about
zirconium in this example,

00:01:04.870 --> 00:01:07.200
and you heat it up.

00:01:07.200 --> 00:01:08.820
So you have it,

00:01:08.820 --> 00:01:11.820
you have a bunch of the
zirconium floating around,

00:01:11.820 --> 00:01:13.300
and then you beam it.

00:01:13.300 --> 00:01:15.800
You will bombard it with
a bunch of electrons.

00:01:15.800 --> 00:01:18.440
And what the electron bombardment does is,

00:01:18.440 --> 00:01:22.410
it can knock off electrons
from the atoms in your sample,

00:01:22.410 --> 00:01:24.240
and it can ionize them.

00:01:24.240 --> 00:01:28.650
And by ionizing some of your
atoms, they now have charge.

00:01:28.650 --> 00:01:30.400
And because they have charge,

00:01:30.400 --> 00:01:34.660
they can be accelerated
through these electric plates.

00:01:34.660 --> 00:01:38.170
So now you have these ions,
in this case, of zirconium,

00:01:38.170 --> 00:01:41.750
moving quite rapidly through this chamber,

00:01:41.750 --> 00:01:44.290
and then they enter into a magnetic field.

00:01:44.290 --> 00:01:47.230
And a magnetic field, a
strong magnetic field,

00:01:47.230 --> 00:01:51.860
can bend the path, can
deflect ions with charge.

00:01:51.860 --> 00:01:52.960
For a given charge,

00:01:52.960 --> 00:01:55.580
the force of the deflection
will be the same.

00:01:55.580 --> 00:01:57.400
But if you have a larger mass,

00:01:57.400 --> 00:01:58.960
you're going to be deflected less.

00:01:58.960 --> 00:02:00.060
And if you have a lower mass,

00:02:00.060 --> 00:02:01.830
you're going to be deflected more.

00:02:01.830 --> 00:02:03.540
And so what you see here

00:02:03.540 --> 00:02:07.430
are the different isotopes being
deflected different amounts

00:02:07.430 --> 00:02:09.940
as they go through the magnetic field.

00:02:09.940 --> 00:02:11.700
And then you have the detector.

00:02:11.700 --> 00:02:14.030
And at different points of the detector,

00:02:14.030 --> 00:02:17.240
you will detect each of these isotopes.

00:02:17.240 --> 00:02:20.460
And the more ions that hit a
certain part of the detector,

00:02:20.460 --> 00:02:22.360
that means that, hey, I have more

00:02:22.360 --> 00:02:24.710
of that type of isotope in nature.

00:02:24.710 --> 00:02:26.110
And then from that,

00:02:26.110 --> 00:02:29.420
you can generate a chart
that looks like this,

00:02:29.420 --> 00:02:32.500
where you see, on the horizontal axis,

00:02:32.500 --> 00:02:35.080
sometimes you'll see
it labeled atomic mass.

00:02:35.080 --> 00:02:37.150
And here, it's in unified
atomic mass units.

00:02:37.150 --> 00:02:39.320
And you can see, when
you put the zirconium

00:02:39.320 --> 00:02:42.420
through the mass spectrometer like this,

00:02:42.420 --> 00:02:46.960
you get a little bit that
has a mass number of 96,

00:02:46.960 --> 00:02:49.670
you have a little bit more
that gets a mass number of 94,

00:02:49.670 --> 00:02:54.220
92, 91, and most of the
zirconium, over 50%,

00:02:54.220 --> 00:02:57.330
has a mass number of 90.

00:02:57.330 --> 00:02:58.570
Now in other cases,

00:02:58.570 --> 00:03:00.940
you won't see it just
in terms of atomic mass,

00:03:00.940 --> 00:03:03.150
given in unified atomic mass units.

00:03:03.150 --> 00:03:05.060
Sometimes in this horizontal axis,

00:03:05.060 --> 00:03:09.350
they'll give it in terms
of mass-to-charge ratio,

00:03:09.350 --> 00:03:11.390
where mass is the mass,

00:03:11.390 --> 00:03:15.240
but then charge is essentially
the charge of the ions.

00:03:15.240 --> 00:03:17.870
Now in a case where your charge is one,

00:03:17.870 --> 00:03:21.070
for example, if you knock
one electron off of the atoms

00:03:21.070 --> 00:03:22.730
and you have a plus-one charge,

00:03:22.730 --> 00:03:25.720
well, then the mass-to-charge
ratio would be the same thing

00:03:25.720 --> 00:03:29.880
as atomic mass measured in
unified atomic mass units.

00:03:29.880 --> 00:03:31.920
If your ions have a different charge,

00:03:31.920 --> 00:03:32.900
well, then you would have

00:03:32.900 --> 00:03:34.800
to make the appropriate adjustment.

00:03:34.800 --> 00:03:36.940
But in introductory chemistry class,

00:03:36.940 --> 00:03:38.970
most of the time you will get things

00:03:38.970 --> 00:03:42.310
in terms of just straight-up atomic mass.

00:03:42.310 --> 00:03:45.500
If you happen to get something
in terms of mass to charge,

00:03:45.500 --> 00:03:48.510
just make sure that if the
charge is, say, plus two,

00:03:48.510 --> 00:03:51.840
that you make the appropriate
adjustment for the masses.

00:03:51.840 --> 00:03:54.670
But this right over here will
tell you the various isotopes,

00:03:54.670 --> 00:03:56.520
and it will tell you its abundance.

00:03:56.520 --> 00:04:00.680
And it all comes from this
process of ionizing those atoms,

00:04:00.680 --> 00:04:04.020
speeding them up, deflecting
them through a magnetic field.

00:04:04.020 --> 00:04:07.060
And the ions that have a
higher mass-to-charge ratio

00:04:07.060 --> 00:04:08.940
will be deflected less,

00:04:08.940 --> 00:04:11.810
and the ions that have a
lower mass-to-charge ratio

00:04:11.810 --> 00:04:13.350
will be deflected more.

00:04:13.350 --> 00:04:16.853
And you can use that information
to make a graph like this.


Making line plots with fractional data

WEBVTT
Kind: captions
Language: en

00:00:00.550 --> 00:00:02.590
- [Instructor] We are
told that for four days

00:00:02.590 --> 00:00:06.570
you record the number of
hours you sleep each night.

00:00:06.570 --> 00:00:11.480
You round each time to the
nearest 1/4 of an hour.

00:00:11.480 --> 00:00:13.632
And then here on this table they tell us

00:00:13.632 --> 00:00:15.460
that our different days,

00:00:15.460 --> 00:00:17.360
they tell us how many hours we slept.

00:00:17.360 --> 00:00:19.030
Day one we slept seven and 1/4 hours,

00:00:19.030 --> 00:00:20.517
day two seven and 3/4,

00:00:20.517 --> 00:00:22.220
day three seven and 3/4,

00:00:22.220 --> 00:00:24.950
day four eight 1/2 hours.

00:00:24.950 --> 00:00:28.080
Then it says, create a line plot

00:00:28.080 --> 00:00:30.140
that shows all of the measurements

00:00:30.140 --> 00:00:31.870
on the number line below.

00:00:31.870 --> 00:00:34.830
And it says click above
the tick marks to add dots,

00:00:34.830 --> 00:00:36.630
click on tick marks to remove dots.

00:00:38.330 --> 00:00:40.548
So we can see if I click right over here,

00:00:40.548 --> 00:00:42.380
a tick mark shows up.

00:00:42.380 --> 00:00:45.720
And if I click again, it gets removed.

00:00:45.720 --> 00:00:50.570
So let's see, day one you
slept seven and 1/4 hours.

00:00:50.570 --> 00:00:53.510
So, that's one day where
you sleep seven and 1/4.

00:00:53.510 --> 00:00:57.390
So, seven and 1/4 is right
between seven and seven and 1/2.

00:00:57.390 --> 00:01:00.880
So that's right over there.

00:01:00.880 --> 00:01:02.480
There we go.

00:01:02.480 --> 00:01:05.610
On day two you sleep seven and 3/4 hours.

00:01:05.610 --> 00:01:09.490
So, that's 1/4, 2/4, 3/4.

00:01:09.490 --> 00:01:11.432
So that's day two.

00:01:11.432 --> 00:01:14.980
Day three you also sleep
seven and 3/4 hours,

00:01:14.980 --> 00:01:18.140
so that's another day that
you sleep seven and 3/4 hours.

00:01:18.140 --> 00:01:20.450
And then on day four you
sleep eight and 1/2 hours,

00:01:20.450 --> 00:01:21.860
which is right over there.

00:01:21.860 --> 00:01:23.640
And so, here we go.

00:01:23.640 --> 00:01:24.940
We have created a line plot

00:01:24.940 --> 00:01:26.600
that shows all of the measurements.

00:01:26.600 --> 00:01:28.800
On one day, day one it was,

00:01:28.800 --> 00:01:31.760
I slept seven and 1/4 hours.

00:01:31.760 --> 00:01:34.257
There were two days where I
slept seven and 3/4 hours,

00:01:34.257 --> 00:01:37.357
and there was one day where
I slept eight and 1/2 hours.

00:01:37.357 --> 00:01:38.963
Let's do another example.

00:01:42.990 --> 00:01:45.960
Amy ran many miles during September.

00:01:45.960 --> 00:01:49.030
She recorded how long it
took her to run each mile,

00:01:49.030 --> 00:01:54.020
rounded to the nearest 1/4 of
a minute on the table below.

00:01:54.020 --> 00:01:55.380
We can see it right over here,

00:01:55.380 --> 00:01:57.610
actually let me move
my window a little bit

00:01:57.610 --> 00:01:58.830
so you can see everything.

00:01:58.830 --> 00:02:00.600
And then it says, create a line plot

00:02:00.600 --> 00:02:04.120
that shows all of the measurements
on the number line below.

00:02:04.120 --> 00:02:07.130
All right, so three times
she was able to run a mile

00:02:07.130 --> 00:02:09.810
in eight and 3/4 minutes.

00:02:09.810 --> 00:02:12.910
So, there are three
that were eight and 3/4.

00:02:12.910 --> 00:02:16.030
Notice, this is, if we
look at the space between

00:02:16.030 --> 00:02:18.860
eight and nine, there is one, two, three,

00:02:18.860 --> 00:02:20.400
four equal intervals.

00:02:20.400 --> 00:02:22.840
And so, 3/4 is going to be three of those.

00:02:22.840 --> 00:02:24.506
One, two, three.

00:02:24.506 --> 00:02:27.970
She ran a mile in eight and
3/4 minutes three times.

00:02:27.970 --> 00:02:29.820
That's what we saw from that table.

00:02:29.820 --> 00:02:32.250
So, that's three times she did that.

00:02:32.250 --> 00:02:36.240
She ran a mile in nine
and 1/4 minutes two times.

00:02:36.240 --> 00:02:39.130
So nine and 1/4.

00:02:39.130 --> 00:02:40.920
That is 1/4 of the way to 10,

00:02:40.920 --> 00:02:44.490
we can see 1/4, 2/4, 3/4, 4/4.

00:02:44.490 --> 00:02:48.350
So nine and 1/4 she did two times.

00:02:48.350 --> 00:02:50.930
So that's going to be one, two.

00:02:50.930 --> 00:02:53.100
And then let's see, nine and 1/2

00:02:54.080 --> 00:02:55.560
she did four times.

00:02:55.560 --> 00:02:58.640
Nine and 1/2 is here, so
one, two, three, four.

00:02:58.640 --> 00:03:02.360
And then eight and 1/2 she did one time.

00:03:02.360 --> 00:03:04.120
So that's eight and 1/2 right over there.

00:03:04.120 --> 00:03:07.430
And then she ran a mile in
nine minutes five times.

00:03:07.430 --> 00:03:08.790
Nine minutes right over here.

00:03:08.790 --> 00:03:12.460
One, two, three, four, five.

00:03:12.460 --> 00:03:13.293
And we're done.


Interpreting line plots

WEBVTT
Kind: captions
Language: en

00:00:00.420 --> 00:00:01.570
- [Instructor] We're told that the weights

00:00:01.570 --> 00:00:05.810
of 11 different babies are
recorded on the line plot below

00:00:05.810 --> 00:00:07.700
and we see there is one, two, three, four,

00:00:07.700 --> 00:00:09.650
five, six, seven, eight, nine,

00:00:09.650 --> 00:00:11.010
10, 11 data points.

00:00:11.010 --> 00:00:13.390
Each one represents a different baby

00:00:13.390 --> 00:00:16.100
whose weight is recorded.

00:00:16.100 --> 00:00:19.510
Each weight was rounded to
the nearest 1/8 of a pound.

00:00:19.510 --> 00:00:21.080
All right, then they ask us,

00:00:21.080 --> 00:00:23.090
what is the difference, in weight,

00:00:23.090 --> 00:00:26.610
between the two heaviest babies?

00:00:26.610 --> 00:00:27.940
So pause this video

00:00:27.940 --> 00:00:28.920
and try to figure that out

00:00:28.920 --> 00:00:31.160
before we work through it together.

00:00:31.160 --> 00:00:34.520
All right, now where are
the two heaviest babies?

00:00:34.520 --> 00:00:35.990
So this one out here,

00:00:35.990 --> 00:00:38.010
this is the heaviest baby,

00:00:38.010 --> 00:00:39.700
and what is its weight?

00:00:39.700 --> 00:00:40.533
Well, let's see.

00:00:40.533 --> 00:00:42.590
Its weight is right over there,

00:00:42.590 --> 00:00:46.060
and what is that number
or what is that weight?

00:00:46.060 --> 00:00:48.970
So this is nine and this is 10,

00:00:48.970 --> 00:00:52.590
and we have one, two, three, four,

00:00:52.590 --> 00:00:56.220
five, six, seven, eight equal spaces.

00:00:56.220 --> 00:00:57.950
So each of these is an eighth.

00:00:57.950 --> 00:01:01.610
So this is nine and one, two,

00:01:01.610 --> 00:01:03.400
nine and 2/8.

00:01:03.400 --> 00:01:05.900
So this one is, let me write this.

00:01:05.900 --> 00:01:07.830
This is nine and 2/8.

00:01:07.830 --> 00:01:09.570
Another way to think about it is,

00:01:09.570 --> 00:01:11.260
2/8 is the same thing as 1/4,

00:01:11.260 --> 00:01:12.093
'cause if you think about it,

00:01:12.093 --> 00:01:15.920
it's one, two, three, four equal spaces.

00:01:15.920 --> 00:01:19.600
This is also nine and
1/4 of the way to 10,

00:01:19.600 --> 00:01:21.833
so this is the same thing as nine and 1/4.

00:01:22.760 --> 00:01:25.670
And then what's the
second heaviest babies?

00:01:25.670 --> 00:01:26.690
'Cause we want the weight difference

00:01:26.690 --> 00:01:28.380
between the two heaviest.

00:01:28.380 --> 00:01:31.040
So the second heaviest
baby is right over here

00:01:31.040 --> 00:01:36.040
and we know that it is
eight and a half pounds.

00:01:36.040 --> 00:01:38.490
So what we really need to do is figure out

00:01:38.490 --> 00:01:42.000
what is the difference
between nine and 2/8

00:01:42.000 --> 00:01:43.660
or nine and 1/4

00:01:43.660 --> 00:01:46.870
and eight and a half right over here?

00:01:46.870 --> 00:01:50.010
So we could set this up as a subtraction.

00:01:50.010 --> 00:01:51.800
This is going to be nine and,

00:01:51.800 --> 00:01:53.900
let's call it nine and 1/4,

00:01:53.900 --> 00:01:57.910
minus, minus eight and a half,

00:01:57.910 --> 00:02:00.140
and we can actually use this,

00:02:00.140 --> 00:02:02.610
this, these measurement scales

00:02:02.610 --> 00:02:03.820
or you can even view this as something

00:02:03.820 --> 00:02:04.800
of a number line

00:02:04.800 --> 00:02:06.320
to help us think about this.

00:02:06.320 --> 00:02:10.580
The difference is this
length right over here.

00:02:10.580 --> 00:02:12.880
And we could think about
it in terms of eighths,

00:02:12.880 --> 00:02:14.970
'cause each of these
hash marks is an eighth,

00:02:14.970 --> 00:02:19.970
so 1/8, 2/8, 3/8, 4/8, 5/8 and 6/8.

00:02:21.800 --> 00:02:24.160
So this is equal to 6/8.

00:02:24.160 --> 00:02:27.150
We could also think about
it in terms of fourths,

00:02:27.150 --> 00:02:32.150
so this is 1/4, 2/4, and 3/4.

00:02:33.250 --> 00:02:36.460
So this is equal to 3/4.

00:02:36.460 --> 00:02:38.040
So what's the difference in weight

00:02:38.040 --> 00:02:40.040
between the two heaviest babies?

00:02:40.040 --> 00:02:43.343
It is 3/4 of a pound.


Line plots with fractions

WEBVTT
Kind: captions
Language: en

00:00:00.690 --> 00:00:02.030
- [Instructor] What we're
going to do in this video

00:00:02.030 --> 00:00:04.900
is review what we know about line plots,

00:00:04.900 --> 00:00:06.920
but apply them in a situation

00:00:06.920 --> 00:00:09.370
where some of our data involves fractions.

00:00:09.370 --> 00:00:11.900
So they tell us the lengths
of some caterpillars

00:00:11.900 --> 00:00:14.380
are shown below, and so we can see

00:00:14.380 --> 00:00:15.960
that here in the line plot,

00:00:15.960 --> 00:00:18.670
just to refresh our minds
how to read a line plot,

00:00:18.670 --> 00:00:21.860
this tells us that we
have two caterpillars

00:00:21.860 --> 00:00:24.240
that are four centimeters long.

00:00:24.240 --> 00:00:26.390
These three show that we
have three caterpillars

00:00:26.390 --> 00:00:28.870
that are seven centimeters long.

00:00:28.870 --> 00:00:31.490
Each dot represents a caterpillar

00:00:31.490 --> 00:00:33.730
whose length we are measuring.

00:00:33.730 --> 00:00:37.650
It allows us to see how those
lengths are distributed.

00:00:37.650 --> 00:00:40.390
For example, we have a lot of
caterpillars at this length.

00:00:40.390 --> 00:00:41.820
What is that length?

00:00:41.820 --> 00:00:44.120
Well we can see that is exactly

00:00:44.120 --> 00:00:46.260
half way between four and five,

00:00:46.260 --> 00:00:50.350
so that is four and one
half centimeters long.

00:00:50.350 --> 00:00:52.230
We divide the section
between four and five

00:00:52.230 --> 00:00:54.140
into two equal sections, and we're going

00:00:54.140 --> 00:00:56.940
one of those two equal
sections towards five,

00:00:56.940 --> 00:00:59.550
so this is four and a half centimeters.

00:00:59.550 --> 00:01:01.880
I can ask you some questions.

00:01:01.880 --> 00:01:04.330
How many total caterpillars were measured?

00:01:04.330 --> 00:01:06.860
Pause this video and think about that.

00:01:06.860 --> 00:01:09.140
Well each dot represents
a caterpillar measurement,

00:01:09.140 --> 00:01:12.260
and we have one, two, three,
four, five, six, seven,

00:01:12.260 --> 00:01:17.120
eight, nine, 10, 11,
12, 13, 14, 15, 16, 17.

00:01:17.120 --> 00:01:19.450
So we have a total of 17 caterpillars.

00:01:19.450 --> 00:01:21.210
Now another question
we could ask ourselves

00:01:21.210 --> 00:01:24.680
is how many of the caterpillars

00:01:24.680 --> 00:01:28.930
are five and one fourth centimeters long?

00:01:28.930 --> 00:01:30.780
Pause the video and think about that.

00:01:31.740 --> 00:01:34.800
Well five and one fourth is
going to be more than five,

00:01:34.800 --> 00:01:37.560
and what we'd want to do to
get to five and one fourth

00:01:37.560 --> 00:01:41.690
is divide the interval or the
length between five and six

00:01:41.690 --> 00:01:43.470
into four equal sections,
they already did that,

00:01:43.470 --> 00:01:46.550
one, two, three, four,
and then we want to go

00:01:46.550 --> 00:01:48.700
one of those four equal sections.

00:01:48.700 --> 00:01:51.130
So five and one fourth is right over here

00:01:51.130 --> 00:01:53.410
and we can see that
there's one caterpillar

00:01:53.410 --> 00:01:56.450
that is five and one
fourth centimeters long.

00:01:56.450 --> 00:01:58.660
We can ask ourselves other questions.

00:01:58.660 --> 00:02:01.830
How many caterpillars,
let me write it over here,

00:02:01.830 --> 00:02:06.080
how many have length

00:02:09.340 --> 00:02:14.340
more than six and one half centimeters?

00:02:15.390 --> 00:02:17.790
Pause the video and try to answer that.

00:02:17.790 --> 00:02:19.760
Where is six and a half centimeters?

00:02:19.760 --> 00:02:23.950
Well, we can divide the
section between six and seven

00:02:23.950 --> 00:02:26.360
into two equal sections, and if you go

00:02:26.360 --> 00:02:28.680
one of those two equal sections,
that is six and a half,

00:02:28.680 --> 00:02:30.580
so that is six and a
half right over there.

00:02:30.580 --> 00:02:32.910
How many have a length
more than or greater than

00:02:32.910 --> 00:02:34.330
six and a half centimeters?

00:02:34.330 --> 00:02:36.660
Well we can see it right over here.

00:02:36.660 --> 00:02:39.830
One, two, three, four, five, six.

00:02:39.830 --> 00:02:41.660
Six of them do.

00:02:41.660 --> 00:02:45.510
And we can even try to
answer questions like

00:02:45.510 --> 00:02:50.510
how many more have a length

00:02:55.180 --> 00:02:58.910
of nine and a half centimeters

00:03:00.424 --> 00:03:04.400
than five and one fourth centimeters?

00:03:04.400 --> 00:03:05.800
Try to answer that question.

00:03:07.130 --> 00:03:08.850
Well nine and a half centimeters,

00:03:08.850 --> 00:03:11.660
that's half way between nine
and 10, right over there.

00:03:11.660 --> 00:03:14.201
We can see two of them have a length of

00:03:14.201 --> 00:03:15.706
nine and a half centimeters.

00:03:15.706 --> 00:03:17.292
And we already know that one of them

00:03:17.292 --> 00:03:18.807
has a length of five and one fourth,

00:03:18.807 --> 00:03:20.930
so how many more have nine
and a half centimeters

00:03:20.930 --> 00:03:22.580
versus five and one fourth?

00:03:22.580 --> 00:03:25.400
Well that would be two
minus one, or one more.

00:03:25.400 --> 00:03:27.160
We have one more caterpillar with a length

00:03:27.160 --> 00:03:28.750
of nine and a half centimeters

00:03:28.750 --> 00:03:31.540
than we do with five and one fourth.

00:03:31.540 --> 00:03:32.460
I'll leave you there.

00:03:32.460 --> 00:03:34.330
We have plenty of examples on Khan Academy

00:03:34.330 --> 00:03:35.753
for you to practice this.


Measure lengths to nearest 1/4

WEBVTT
Kind: captions
Language: en

00:00:00.320 --> 00:00:02.410
- [Instructor] We are
asked what is the height

00:00:02.410 --> 00:00:03.950
of the sunflower?

00:00:03.950 --> 00:00:06.420
So pause this video and think about it.

00:00:06.420 --> 00:00:07.690
All right, so let's see.

00:00:07.690 --> 00:00:11.000
The bottom of the
sunflower is right aligned

00:00:11.000 --> 00:00:12.310
with the bottom of the ruler,

00:00:12.310 --> 00:00:14.140
so there ruler's in the right place.

00:00:14.140 --> 00:00:15.670
And let's see, the sunflower goes

00:00:15.670 --> 00:00:18.610
all the way up to this
point right over here.

00:00:18.610 --> 00:00:23.610
So this is one, two, three, four, five,

00:00:24.210 --> 00:00:26.320
and then a little bit more.

00:00:26.320 --> 00:00:27.530
So we're going to get into a fraction.

00:00:27.530 --> 00:00:29.522
So what is this extra amount?

00:00:29.522 --> 00:00:33.098
So if we can see the space between five

00:00:33.098 --> 00:00:38.050
and six is divided into
four equal sections.

00:00:38.050 --> 00:00:41.860
So we have, one, two, three, four.

00:00:41.860 --> 00:00:42.810
Or we could see it here.

00:00:42.810 --> 00:00:45.850
They've divided it with
these little hash marks

00:00:45.850 --> 00:00:49.600
into one, two, three, four equal sections.

00:00:49.600 --> 00:00:52.850
And this goes one of
those four equal sections

00:00:52.850 --> 00:00:57.850
towards six, so this is 5 1/4 feet.

00:00:58.450 --> 00:01:01.630
That's how tall the sunflower is.

00:01:01.630 --> 00:01:04.603
All right, let's do another example.

00:01:07.410 --> 00:01:10.680
So here we are told, or we are asked,

00:01:10.680 --> 00:01:14.200
which pencil measures 2 3/4 of an inch?

00:01:14.200 --> 00:01:17.320
So pause this video and
try to think about it.

00:01:17.320 --> 00:01:21.510
All right, so we go one inch, two inches,

00:01:21.510 --> 00:01:23.050
and then we have to think about how far

00:01:23.050 --> 00:01:25.930
between two and three is 3/4?

00:01:25.930 --> 00:01:27.300
So to think about 3/4, we have

00:01:27.300 --> 00:01:29.900
to divide the part, or
the part of this ruler,

00:01:29.900 --> 00:01:33.170
between two and three
into four equal sections.

00:01:33.170 --> 00:01:34.360
So let's see.

00:01:34.360 --> 00:01:37.380
If I were to just split it like this,

00:01:37.380 --> 00:01:39.330
that's two equal sections.

00:01:39.330 --> 00:01:40.260
So if I were to take each

00:01:40.260 --> 00:01:41.750
of those two equals sections

00:01:41.750 --> 00:01:45.740
and then split them, now
that's four equal sections.

00:01:45.740 --> 00:01:50.740
Notice one, two, three,
four equal sections.

00:01:52.000 --> 00:01:54.800
So when we're thinking about 3/4,

00:01:54.800 --> 00:01:57.170
we wanna go three of
those four equal sections.

00:01:57.170 --> 00:02:00.150
One, two, three.

00:02:00.150 --> 00:02:03.070
And so you can see right over here,

00:02:03.070 --> 00:02:06.880
that is 2 3/4.

00:02:06.880 --> 00:02:09.700
This is 2 3/4 right over here.

00:02:09.700 --> 00:02:11.773
And that is pencil A.


Multiplication and division relationship for fractions

WEBVTT
Kind: captions
Language: en

00:00:00.180 --> 00:00:02.040
- [Instructor] You are
likely already familiar

00:00:02.040 --> 00:00:05.360
with the relationship between
multiplication and division.

00:00:05.360 --> 00:00:09.230
For example, we know that three times six

00:00:09.230 --> 00:00:11.600
is equal to 18.

00:00:11.600 --> 00:00:16.080
But another way to express
that same relationship

00:00:16.080 --> 00:00:19.700
is to say, all right, if
three times six is 18,

00:00:19.700 --> 00:00:23.640
then if I were to start with
18 and divide it by three,

00:00:23.640 --> 00:00:25.540
that would be equal to six.

00:00:25.540 --> 00:00:27.840
Or you could say something like this,

00:00:27.840 --> 00:00:30.980
that 18 divided by,

00:00:30.980 --> 00:00:34.090
divided by six

00:00:34.090 --> 00:00:37.730
is equal to three.

00:00:37.730 --> 00:00:41.050
Now we're just going to
extend this same relationship

00:00:41.050 --> 00:00:43.840
between multiplication and division

00:00:43.840 --> 00:00:47.820
to expressions that deal with fractions.

00:00:47.820 --> 00:00:50.150
So for example,

00:00:50.150 --> 00:00:55.150
if I were to tell you that 1/4 divided by,

00:00:55.610 --> 00:01:00.040
and I'm going to color-code
it, divided by two

00:01:00.040 --> 00:01:02.440
is equal to 1/8,

00:01:02.440 --> 00:01:04.530
is equal to 1/8,

00:01:04.530 --> 00:01:06.830
how could we express this relationship,

00:01:06.830 --> 00:01:08.823
but using multiplication?

00:01:09.960 --> 00:01:13.520
Well, if 1/4 divided
by two is equal to 1/8,

00:01:13.520 --> 00:01:18.410
that means that 1/8 times
two is equal to 1/4.

00:01:18.410 --> 00:01:21.030
Let me write this down, or
I could write it like this.

00:01:21.030 --> 00:01:26.030
I could write that 1/4
is going to be equal to,

00:01:26.580 --> 00:01:31.160
is going to be equal to 1/8 times two,

00:01:31.160 --> 00:01:33.580
times two.

00:01:33.580 --> 00:01:35.970
And we could do another example.

00:01:35.970 --> 00:01:38.840
Let's say that I were to
walk up to you on the street

00:01:38.840 --> 00:01:43.650
and I were to tell you that, hey, you, 42

00:01:43.650 --> 00:01:45.270
is equal to

00:01:46.200 --> 00:01:48.040
seven,

00:01:48.040 --> 00:01:52.030
seven divided by 1/6.

00:01:52.030 --> 00:01:55.230
In the future, we will learn
to compute things like this.

00:01:55.230 --> 00:01:57.330
But just based on what you see here,

00:01:57.330 --> 00:02:00.070
how could we express
this same relationship

00:02:00.070 --> 00:02:03.190
between 42, seven, and 1/6,

00:02:03.190 --> 00:02:04.870
but express it with multiplication?

00:02:04.870 --> 00:02:06.753
Pause this video, and think about that.

00:02:08.070 --> 00:02:12.760
Well, if 42 is equal to
seven divided by 1/6,

00:02:12.760 --> 00:02:16.340
that means that 42 times 1/6

00:02:16.340 --> 00:02:18.320
is equal to seven.

00:02:18.320 --> 00:02:19.410
Let me write that down.

00:02:19.410 --> 00:02:24.410
This is the same relationship
as saying that 42 times

00:02:24.621 --> 00:02:26.120
1/6,

00:02:26.120 --> 00:02:29.180
1/6 is equal

00:02:29.180 --> 00:02:30.913
to seven.

00:02:32.020 --> 00:02:34.210
Now let's say I walk
up to you on the street

00:02:34.210 --> 00:02:36.560
and I were to say, all right, you,

00:02:36.560 --> 00:02:40.890
I'm telling you that 1/4 divided by,

00:02:40.890 --> 00:02:42.980
divided by six

00:02:42.980 --> 00:02:45.310
is equal to some number

00:02:45.310 --> 00:02:48.860
that we will express as t.

00:02:48.860 --> 00:02:53.620
So can we rewrite this relationship
between 1/4, six, and t,

00:02:53.620 --> 00:02:56.560
but instead of using
division, use multiplication?

00:02:56.560 --> 00:02:59.150
Pause this video, and
try to think about it.

00:02:59.150 --> 00:03:03.000
So if 1/4 divided by six is equal to t,

00:03:03.000 --> 00:03:05.200
based on all of the
examples we've just seen,

00:03:05.200 --> 00:03:08.210
that means that if we
were to take t times six,

00:03:08.210 --> 00:03:10.210
we would get 1/4.

00:03:10.210 --> 00:03:14.260
So we could write it
this way, t times six,

00:03:14.260 --> 00:03:19.260
times six is going to be equal to 1/4.

00:03:19.280 --> 00:03:20.630
If this isn't making sense,

00:03:20.630 --> 00:03:23.240
I really want you to think
about how this relationship

00:03:23.240 --> 00:03:26.260
is really just the same
relationship we saw up here.

00:03:26.260 --> 00:03:27.820
The only new thing here is

00:03:27.820 --> 00:03:29.840
instead of always having whole numbers,

00:03:29.840 --> 00:03:31.070
we're having fractions

00:03:31.070 --> 00:03:34.753
and representing some of
the numbers with letters.


Fraction division in context

WEBVTT
Kind: captions
Language: en

00:00:00.380 --> 00:00:01.750
- [Instructor] We're told that a group

00:00:01.750 --> 00:00:05.480
of three friends is
practicing for the track meet.

00:00:05.480 --> 00:00:10.090
The group is going to
run 1/2 of a mile total.

00:00:10.090 --> 00:00:13.310
If they each run the same distance,

00:00:13.310 --> 00:00:16.360
how far will each person run?

00:00:16.360 --> 00:00:19.450
Which expression could
represent this situation?

00:00:19.450 --> 00:00:22.663
So pause this video and try to
figure this out on your own.

00:00:23.730 --> 00:00:25.690
All right, the way I think about it is

00:00:25.690 --> 00:00:29.380
there's some distance that
they're going to try to travel.

00:00:29.380 --> 00:00:31.480
So in this case, it's half of a mile

00:00:31.480 --> 00:00:33.490
and they're going to divide that distance

00:00:33.490 --> 00:00:35.680
amongst the three friends.

00:00:35.680 --> 00:00:37.920
And so the distance that
each of them are going to run

00:00:37.920 --> 00:00:39.720
is the total distance divided

00:00:39.720 --> 00:00:42.070
by the number of folks that are running.

00:00:42.070 --> 00:00:44.990
So an expression that
represents this is 1/2,

00:00:44.990 --> 00:00:47.100
the total distance they're running,

00:00:47.100 --> 00:00:49.880
divided by the number of people

00:00:49.880 --> 00:00:53.460
who are going to split that
distance, divided by three.

00:00:53.460 --> 00:00:57.150
And so that is choice C right over here.

00:00:57.150 --> 00:00:58.760
Now it might have confused you a little

00:00:58.760 --> 00:01:02.420
because you're not used to
dividing a smaller number,

00:01:02.420 --> 00:01:05.380
especially a fraction, by a lager number

00:01:05.380 --> 00:01:07.250
but that's exactly what's
going on over here.

00:01:07.250 --> 00:01:08.800
You're taking the total distance

00:01:08.800 --> 00:01:11.550
and it's being split
amongst three friends.

00:01:11.550 --> 00:01:14.740
So the total distance
divided by three friends

00:01:14.740 --> 00:01:18.580
will tell you how far
each of them has to run.

00:01:18.580 --> 00:01:20.563
Let's do another example.

00:01:21.980 --> 00:01:25.270
So here, we are, actually
they're telling us

00:01:25.270 --> 00:01:27.100
that there's some problem
that can be solved

00:01:27.100 --> 00:01:28.690
with 1/2 divided by seven.

00:01:28.690 --> 00:01:30.240
They say which problem can we solve

00:01:30.240 --> 00:01:31.890
with 1/2 divided by seven?

00:01:31.890 --> 00:01:34.400
And then they give us
three different scenarios

00:01:34.400 --> 00:01:36.050
that we could try to solve.

00:01:36.050 --> 00:01:37.460
So pause this video and think

00:01:37.460 --> 00:01:38.890
of which of these three scenarios

00:01:38.890 --> 00:01:41.463
can be solved with this expression.

00:01:42.560 --> 00:01:45.200
All right, let's go through
each of the choices.

00:01:45.200 --> 00:01:49.680
Cara ordered seven pizzas
for her birthday party.

00:01:49.680 --> 00:01:53.840
Her parents ate 1/2 of a
pizza before the party.

00:01:53.840 --> 00:01:58.020
How much pizza is left for the party?

00:01:58.020 --> 00:01:59.400
All right, so what's going on here?

00:01:59.400 --> 00:02:03.280
She started with seven
pizzas, she starts with seven.

00:02:03.280 --> 00:02:06.340
Her parents ate 1/2 of a pizza.

00:02:06.340 --> 00:02:09.550
So 1/2 of a pizza is taken away.

00:02:09.550 --> 00:02:12.090
And so that would tell
you how much is left.

00:02:12.090 --> 00:02:14.580
So this is definitely,
this is the expression

00:02:14.580 --> 00:02:16.910
you would solve to figure out A,

00:02:16.910 --> 00:02:18.380
not this expression up here.

00:02:18.380 --> 00:02:20.320
So I would rule this out.

00:02:20.320 --> 00:02:22.140
Walt has seven hamsters.

00:02:22.140 --> 00:02:25.250
Each hamster weighs 1/2 of a kilogram.

00:02:25.250 --> 00:02:28.110
What is the total weight of the hamsters?

00:02:28.110 --> 00:02:29.330
Well to figure out the total weight,

00:02:29.330 --> 00:02:31.570
you would start with
the number of hamsters

00:02:31.570 --> 00:02:32.850
and you would multiply that

00:02:32.850 --> 00:02:35.200
times the weight of each hamster.

00:02:35.200 --> 00:02:37.080
So that would be seven times 1/2,

00:02:37.080 --> 00:02:38.750
so we could rule that one out.

00:02:38.750 --> 00:02:40.250
So it's likely going to be C

00:02:40.250 --> 00:02:42.671
but let's figure this, let's
make sure it makes sense.

00:02:42.671 --> 00:02:47.671
Jenae has 1/2 kilogram of trail mix.

00:02:48.010 --> 00:02:52.060
She splits her trail mix
evenly between seven friends.

00:02:52.060 --> 00:02:55.660
How much trail mix will each friend get?

00:02:55.660 --> 00:02:59.440
All right, she has a total
amount, 1/2 of a kilogram

00:02:59.440 --> 00:03:01.740
and she's going to
divide that total amount,

00:03:01.740 --> 00:03:05.550
she splits her trail mix
evenly between seven friends

00:03:05.550 --> 00:03:08.600
so she's going to take this
1/2 and split it evenly

00:03:08.600 --> 00:03:13.330
amongst seven friends to get
a certain amount per friend.

00:03:13.330 --> 00:03:15.260
How much trail mix will each friend get?

00:03:15.260 --> 00:03:17.810
And that's exactly what
that expression up there is

00:03:17.810 --> 00:03:20.453
so I am liking this choice.