In this video,
we're going to look at how to draw dot structures
of simple organic molecules that have single bonds. So if I look at the molecular
formula CH4, which is methane, and I want to draw a dot
structure for the methane molecule, I would go over here
to my organic periodic table and find carbon. And I can see carbon
is in group IV. Therefore, carbon will have
four valence electrons. So I can draw a carbon with
its four valence electrons around it like that. Remember from general
chemistry, valence electrons are the electrons in the
outermost energy level. So carbon has four
valence electrons in its outermost energy level. Next, I have to
think about hydrogen. And hydrogen is in group
I on the periodic table. Therefore, hydrogen will
have one valence electron. And so I can go ahead and
put a hydrogen in there with one valence electron. And I know I have to do
that three more times. So I keep putting in hydrogens,
each with one valence electron, so a total of four hydrogens. And now I can start
connecting my dots. I know that two
valence electrons equals one single covalent bond. So there is a single
covalent bond. There is a single covalent bond. And then I have two more here. So this is my complete
dot structure for methane. Now I can see that carbon is
surrounded by eight electrons here. So we can go ahead
and highlight those. So if I'm counting the
electrons around carbon, it would be two, four,
six, and eight, like that. And eight electrons
around carbon makes carbon very stable. And if we look at the periodic
table, we can see why. So if I look at
the second period, I can see that the valence
electrons for carbon would be one, two,
three, and four. And to get to
eight electrons, we would go five,
six, seven, eight. So if carbon is surrounded
by eight electrons, it's like it has the
electron configuration of a noble gas, which
makes it very stable, because all of the orbitals in
that energy level are now full. So an octet of electrons
is the maximum number of electrons for carbon. If we look at
hydrogen, we can see that each hydrogen is
surrounded by two electrons. And so if I find
hydrogen here, hydrogen is in the first energy level. And so here's one electron
and here's two electrons. So in the first energy level,
there is only an s orbital. And so that s orbital holds
a maximum of two electrons. And we get to the electron
configuration of a noble gas. And so hydrogen is stable
with having only two electrons around it. Let's look at another
dot structure. And let's do one that
has nitrogen in it. So if I look at the
molecular formula CH3 NH2, I'm going to once
again start with carbon in the center with its four
valence electrons around it, like that. And I know that there are
three hydrogens on that carbon. So I can go ahead and put
in those three hydrogens. Each hydrogen has one
valence electron, like that. And then on the right side, I'm
going to think about nitrogen. So I need to find nitrogen
on my periodic table. Nitrogen is in
group V. Therefore, nitrogen has five
valence electrons. I can represent those
valence electrons as one, two, three, four,
and five, like that. And I still have two hydrogens
to worry about, right? So I have still have
these two hydrogens here. And I can see there's a place
for them on the nitrogen. So I can go ahead and
put a hydrogen in here and a hydrogen in here,
and connect the dots. And I have my dot structure. And I can also check
on my octet rule. So carbon has an octet. And nitrogen has
an octet as well. So let's go ahead
and verify that. So there's two electrons
here, four, six, and eight. So nitrogen is in
the second period. And so nitrogen is also going
to follow the octet rule when you're drawing your
dot structures. Let's do one with oxygen next. So if I wanted to draw the
dot structure for methanol, methanol is CH3 OH. And so once again,
I start with carbon with the four valence electrons. And I have three hydrogens, each
one with one valence electron, like that. And so I can go ahead and
put in those three hydrogens. Next I have oxygen. So I need to find oxygen on
my organic periodic table. And I can see that oxygen
is in group VI right here. So oxygen is going to have six
valence electrons around it. So I can go ahead
and draw in oxygen. And I can put its six
valence electrons in-- one, two, three, four, five,
and six, like that. And then I'm going to put
in the hydrogen, right? So now I have a
hydrogen to worry about. And I know that hydrogen
has one valence electron. So I can see there's a
place for it over here. And once again, I
can connect the dots and see all of the
single covalent bonds in this molecule. So that's one bond. That's another bond. And then I can see the carbon
has bonded to the oxygen. And the oxygen has bonded
to this hydrogen as well. Again, we can check
our octet rule. So the carbon has eight
electrons around it. And so does the oxygen. So this would be two
right here, and then four, and then six, and then eight. So oxygen is going to
follow the octet rule. Now when you're
drawing dot structures, you don't always have to
do this step where you're drawing each individual
atom and summing all of your valence
electrons that way. You can just start drawing it. So for an example, if I gave
you C2 H6, which is ethane, another way to do
it would just be starting to draw
some bonds here. And so I have two carbons. And it's a pretty good
bet those two carbons are going to be connected
to each other. And then I have six hydrogens. And if I look at what's
possible around those carbons, I could put those six hydrogens
around those two carbon atoms, like that. And if I do that, I'll have an
octet around each carbon atom. So this would be my dot
structure for ethane. To double check yourself,
you could make sure that your dot structure
has the correct number of valence electrons. So if I'm thinking
about each carbon having four valence electrons
and I have two of them, I'm going to get eight valence
electrons from those two carbons that I have to
represent in my dot structure. Each hydrogen has
one valence electron. And I have six of
them, so I need to worry about six valence
electrons from the hydrogen, so for a total of 14. So when I look at
my dot structure, I can check to make sure
I have the correct number of valence electrons. I need 14. So let's go ahead
and count them. So this would be two here,
four, six, eight, 10, 12 and 14. So I have the correct number of
valence electrons represented in my dot structure. I also have an octet of
electrons around my carbons. And so this would be the
dot structure for ethane.