Hi guys, welcome back.
This time around we are gonna continue our
discussion on the language chemistry, and
in particular we are gonna be
looking at chemical bonds.
Forward to that, let's take a few moment
just to reflect on what we already know.
We know that there are a number of
elements that we can identify from
the periodic chart.
There's a number of things from the
periodic chart that we could identify such
as the Atomic Symbol, which are the
letters that represent a given element.
The Atomic Number,
which tells us the number of protons, and
the number of electrons as
read from the periodic chart.
And the Atomic Weight, which we can round
out to get to the number of neutrons.
We know that these elements can be
found in our body as electrolytes.
Such as sodium and potassium.
We also know that they can work
together to create larger structures,
known as molecules.
These molecules can be molecules
of an element or a compound.
We further know that the individual
compounds get intermixed
physically that make mixtures.
And we identify three types of mixtures.
So we have solutions,
suspensions and colloids.
Now we need to back up and say what
is this relationship that allows for
given atoms of elements, to interact
with one another to make compounds?
And when we're talking
about elements doing this,
it all deals with the stability factor.
As read from the periodic chart, we know
that each element is electron neutral.
But is it stable as read
from the periodic chart?
And to be able to answer that question,
we've got to first identify
what are chemical bonds, and
what is it about a chemical bond
that makes an element stable.
A chemical bond is gonna represent
an energy relationship between electrons
of reacting atoms.
Not just any electrons, but it's gonna
be those electrons that are going to be
found on the outermost
energy level of that atom.
These electrons are going to be
known as the Valence Electrons.
And they're going to be found in the
energy level known as the valence shell.
The valence shell will be
the outermost energy level.
It will contain the electrons
that are capable of having inner
relationship with other atoms.
A reaction, an energy relationship
recent known as chemical bonds.
What governs whether an atom is gonna
be chemically active with other atoms.
Well, that's something
known as an Octet Rule.
And octet rule says for
an atom to be stable,
it must obey one of two rules
associated with the octet rule.
The first rule would be that
the outermost energy level is full.
The second rule would be that
the outermost energy level has 8
electrons in it.
If either part of this rule
are obeyed by an atom,
then that atom is not gonna
be reactive in nature.
It's gonna be stable in nature, and
it's going to be known as a noble gas or
an inert gas.
The vast majority of elements that
we look at on the periodic chart,
are not gonna obey the rule of eight.
So they're gonna have chemical
relationships, energy relationships,
with other atoms, in such a way in which
they can satisfy the rule of eight,
by having that relationship.
Let's look at a few examples of
how this can happen in nature.
Let's start by looking at hydrogen.
When you take a look at atom of hydrogen,
how many protons are found
the atom of hydrogen?
I hope you tell me 1.
And as written from the periodic chart,
every element is electro-neutral,
so if there is one proton,
there must be one electron.
Now where would that electron be found?
It would be found orbiting the atomic
nucleus of that atom of hydrogen,
and it would be fighting what
we know as energy levels.
Now the question would be then,
if you have 1 electron in the outermost
energy level of hydrogen,
then the valence electron for
hydrogen would be 1, and
the energy level in this case would be 1.
And this first energy level,
is gonna hold 2 electrons to be full.
So is hydrogen atoms stable in nature,
as written from the periodic chart?
Does it obey the rule of eight?
It does not, because the outermost
energy level in this case
holds 2 to be full and
it only has 1 with hydrogen.
Now let's look at helium,
how many protons are found in an atom
of helium, hope you tell me 2.
Number of electrons, 2.
This does electrons and
their first energy level, cuz we
always fill up the first energy level,
before we go to the next energy level.
Now, is helium table as written
from the periodic chart,
it is electron neutral but is it stable?
Does it obey the rule of eight?
The rule of eight says the atom most
energy level needs to be full, or
obtain, or have eight electrons in it.
In this case, the first energy level
only holds 2 electrons to be full.
So helium actually is stable in nature.
It's known as a noble gas or inert gas.
Let's look at lithium.
Lithium has 3 protons.
It has 3 electrons.
So let's put those electrons in.
The first two go on
the first energy level, and
the third one then goes into
the second energy level.
The second energy level to
be full holds 8 electrons.
Lithium is stable as written
from the periodic chart.
To be stable, again it has to have
outer energy level must be full or
its outer energy level
must total 8 electrons.
So lithium is not stable, but how many
valance electrons does lithium has then?
It has 1 valence electron.
This one in the outermost energy level,
and what is the outermost energy level?
The outermost energy
level is the second one.
Let's look at beryllium.
Beryllium has 4 protons, has 4 electrons.
The first two go into first energy level.
The other two will go in
the second energy level.
Notice I'm putting them as far
away from one another as I can.
How many valance electrons
does beryllium have?
It has 2 electron, valence electrons.
The valence electrons are those
found in the outermost energy level.
Is beryllium stabilize written
from the periodic chart?
Hope you tell me no, because the outer
entry level does not have 8 in it nor
is it full.
Because this outer energy
level holds 8 to be full.
What is the valence shell, 2.
Let's go to boron.
Boron has 5 protons, it have 5 elections.
Let's put those electrons in place.
The first two go here, the last three
go into the second energy level.
So how many valence
electrons does boron have?
It has 3.
And what energy level are those
valence electrons found in?
The second one.
Is it stable?
No, go to carbon.
How many protons does it have?
It has 6.
How many electrons does it have?
It has six.
That first two electrons in the first
energy we level fill it up,
we move to the next energy level which
is the second energy level that holds
a maximum of 8 but, in this case for
carbon, it will hold the remaining four.
So the valence electrons in
the carbon atom are gonna be 4.
And the valence energy shell
is gonna be the second one.
Look at nitrogen.
How many protons?
It has 7.
How many electrons?
It has 7.
The first two go here, and
in the first energy level, and
then the remaining five go
into the second energy level.
So how many valence electrons
does nitrogen have?
It has five, those are the five
in the outer energy level.
And the outer energy level of the valence
shell is gonna be the second one.
Take a look at oxygen.
Oxygen has eight proton,
it has eight electrons.
The first two electrons go
in the first energy level.
The remaining six go into
the second energy level,
the number of valence electrons
in an atom of oxygen is six,
and the valence shell is the second one.
Look at fluorine, fluorine has 9 protons,
it has 9 electrons.
The first two of those nine electrons
go in the first energy level.
The remaining 7 go in
the second energy level.
Now here is the number of valence
electrons that are found in the animal
fluorine, is gonna be 9 or 7?
Hope you tell me 7,
because it's only going, the valence
electrons are only those electrons
found in the outermost energy level.
With just a second energy level.
This fluorine stable as written
from the periodic chart?
No, because it does not
obey the rule of eight.
It does not have 8 electrons
in the centermost shell, nor
is the outermost shell full.
Look at neon.
Neon has 10 protons.
10 electrons, the first two
go in the first energy level.
Then we put the remaining 8 out
here in the second energy level.
How many valance electrons does neon have?
It has 8,
they're found in the second energy level.
Is neon stable as written for
the periodic chart?
I hope you tell me yes, because it replace
the rule of eight or the octet rule, with
says it has to have either eight electrons
win its outermost shell, which it does.
Or its outermost shell have to be
full which in this case it is full,
because the second energy
level only holds 8 electrons.
Now let's look at sodium.
Sodium has 11 protons, has 11 electrons.
The first two go into first energy level,
the next 8 go in the second energy level.
That energy level is gonna be
full with those 8 electrons.
So the third energy level
has to be brought into play.
And so
that it can hold the remaining electron.
So while it has 11 electrons,
how many valence electrons
does an atom of sodium have?
It has one valence electron, and
what energy level is it gonna be found in?
It will be found in the third one.
The last one we'll look at is magnesium.
Magnesium has 12 protons and 12 electrons.
The first two go in
the first energy level.
The next 8, go in the second energy level.
And that leaves us with two to
go in the third energy level.
I think valence electrons are going
to be found in argon, magnesium,
hope you tell me 2,
I mean electrons in an atom of magnesium.
Hope you tell me 12, what energy level
will the valence electrons be found in?
I hope you will tell me the third one.
Now that you've had a chance to actually
look at several examples of elements and
how we can identify the valence electrons,
using energy shells and
drawing our circles.
Got a quick question for you.
Is there a way which we can cheat by using
a periodic chart, to help us identify
the valence of electrons and
valence shell without drawing a circles.
We go back and look at periodic chart, and
if you recall a periodic chart that's
gonna be the elements that we had in
a fine periodic chart based on columns and
a row sequence.
Now go back to what our examples were.
Look at hydrogen.
Look at lithium.
And take a look at sodium.
How many valence electrons
did each of those have?
If you recall they had one.
Now what column is hydrogen, lithium and
sodium, they're in column 1.
So the column will tell us
the number of valence electrons.
Let's try that out, let's go over and
look at carbon in this example.
What column is carbon in?
Roman numeral four.
How many valence electrons does it have?
Four.
Look at nitrogen.
What column is it in?
Roman numeral five.
And the electrons does it have in
his outer shell, valence electrons?
Five.
So we can use the column number, to
tell us the number of valence electrons.
Now tell me,
what's the difference between hydrogen and
lithium as far as where that
valence electron's founded.
Where hydrogen is found in the first
energy level, lithium is found in
the second energy level and then sodium
was found in the third energy level.
Now take a look at the periodic chart.
What row's hydrogen in?
One.
What row's lithium in?
Two.
What row's sodium in?
Three.
So catch it, you can find out the number
of valence electrons in a given
atom of an element by
looking at it's column.
And you can determine which energy
level that valence electron's found,
in by looking at the row it's in.
Try that out, go look at sulfur.
Sulfur has an atomic symbol of S,
how many valence electrons does it have?
In what energy level would those
valence electrons be found in?
I hope you tell it me it has
6 valence electrons, and
I hope you tell me they're gonna be
found in the third energy level.
Try that out for potassium.
How many valence electrons,
what energy level?
I hope you tell it's got 1 valence
electron in energy level number 4.
Finally, take a look at bromine,
which is Br.
Number of valence electrons, 7.
Energy level, 4.
Have a good day.
See you.
