Carbon as a building block of life | Properties of carbon | Biology | Khan Academy

You're probably already familiar with
some forms of carbon. For example this graph I write over here, this is one form carbon takes. Very
important when you're writing with a pencil, otherwise you would not see any
writing. If you didn't have the graphite scraping onto your, scraping onto your paper, which you and
your paper is also. It's not pure carbon, but it has a lot of carbon in it. This right over here is a raw
diamond, another form the carbon can take under
intense time or after a long period of time under intense pressure. But what you may or may not
realize is that carbon is actually essential for
life. In fact life as we know it is carbon-based, so carbon-based, based life. When we look for signs of
life, at least life as we know on other planets,we are looking for signs of
carbon-based life. And there might be other forms, other other elements that form the backbone of

But carbon is the only one that we have been able to observe. Now
why is carbon so valuable for life? Why does
it form the backbone of the molecules that make life
possible ? What all comes down to where it sits in the periodic table? And how many and its atomic number and how it tends
to bond with things? So this is why Chemistry is important.
So carbon we see over here has an atomic number six, which by definition means it has 6
protons. So far we draw its nucleus it would
have 1,2 , 3, 4, 5, 6 protons. And the most common isotope of carbon on earth is carbon 12, which also has six neutrons. So let
me draw that in this nucleus 1, 2, 3, 4, 5, 6 neutrons. And then neutral carbon is going to have six electrons. And so two of them are going to be in
their inner most in the first shell .So that's two of them right over

These are the inner
shell. I guess you could say or the so that's the first two electrons ,and
then you have four remaining in its outermost shell. And these four considered valence
electrons, these are the electrons that actually do the reacting. And if any of this seems
unfamiliar to you,I encourage you to watch the videos on Khan Academy on things
like valence electrons, but this is a little
bit overview right over here. Carbon has four valence electrons.
Valence electrons are the ones that do or that tend to do the
reacting. And so I could if I wanted to simplify
this drawng over here,I could say ,"Okay carbon."And if I register as valence
electrons which is a typical thing to do. I could say carbon has 1, 2, 3 ,4 valence electrons. Now you might remember the octet rule that that atoms tend to be more stable when
they at least pretend, like they with that they're sharing or that they
have eight electrons in there outermost shell. So carbon can do that by forming 4
covalent bonds.

For example it could do that with
hydrogen.This hydrogen over here has one valence electron. It actually has one
electron. Now the hydrogen feels good. It feels like its sharing two-electrons
filling its its first shell .Hydrogen is just trying to fill out the first shell, feel a little bit more like helium
and now carbon says," Oh,now I get to share share this electron." And then carbon can do it again with another hydrogen. It can do it again with another
hydrogen. And it can do it again with another hydrogen. So now carbon can feel like," Hey I'm sharing eight
electrons and the each of the hydrogens feel like, "Oh look you know I I'm sharing two electrons." Everyone seems to be happy
everyone seems to be stable. And this molecule right over here, this
is methane ,this is methane. And by definition because it involves
carbon it is considered an organic molecule. It is considered an organic molecule. In
fact, the whole the whole field of Organic Chemistry is
all about studying organic molecules which are molecules
that have carbon. Now because this only has carbon and
hydrogen in it,it is also considered to be a Hydrocarbon.

Hydrocarbon Hydrocarbon. And you might be familiar with things
like gasoline being considered a Hydrocarbon. And it is indeed a Hydrocarbon. In fact gasoline gasoline actually even even methane could be used as fuel right over here. But in
typically you can see these long chains of hydrocarbons. For example, you could have 8 carbons
form octane. You might be familiar things like high octane fuel. So let's see carbon 2, 3, 4, 5, 6, 7, 8. This is a hydrocarbon. Its Octane because it has 8 carbons Oct, Octane. In all the
other bonds remember carbon forms 4 bonds. It typically forms 4 bonds. So now that carbon has 4 bonds. Now this
carbon has 4 bonds. Now this carbon 2 of them to hydrogen ,2 of them to carbon.2 to hydrogen, 2 to carbon. Hopefully this starts to give you an
appreciation why carbon is so useful as a building block
because it can form so many bonds with so many different structures.

And these hydrocarbons they can be
chains or they can even form, they can even form rings they can form
cycles.And in things like graphite and in diamond carbons can form
these lattice structures, where you know know carbon is for is bonding. Carbon is forming is bonding
to more than two carbons in these three
dimensional shapes. In these three, in these three
dimensional shapes. And the shape because it's
forming three bonds that that carbon typically forms bonds in
these are called tetrahedral shapes or tetrahedral

And when someone says tetrahedron if someone says tetrahedron they're
talking about they're talking about a..Wait let me use
a different color. So a tetrahedron is a three-dimension, a three-dimensional
shape that has four sides each of which are triangles. Each of which are triangles. So it
would look like this. You could do it as a pyramid with a triangular base. A pyramid with a triangular base. And
when carbon forms bonds as in the case have this methane right over here. I'd rather the carbon in the middle as this, yellow circle ,then each of the hydrogens over here are going to be at the corners or at you say the vertices of
the tetrahedron.

And so this is the tetrahedral shape
that carbon is actually forming. Of course you have
these co valent bonds right over here. Let me do this in a different color. You
have these covalent bonds over here and we could draw it like this. We could
draw these covalent bonds like this. That's 1 of them, maybe that's this one over here. This one over here is right over here.These electrons are all just buzzing around. And then the one we have over here and then you have one over here. So you might see methane sometimes just drawn like this. You might just see it drawn, you might just see it drawn like this. But it's really forming, it's really forming
a tetrahedral a tetrahedral shape.

Me finished drawing it, so hydrogen hydrogen hydrogen hydrogen where each of these lines represent a pair of
e electrons here. Eight electrons being shared in
aggregate, but the actual shape is closer to this. Now I'm claiming to you that it's the
backbone of life or life as we know it. And its
even the back bone of life is as you are. Life in the form of you. We've
already talked about you being a majority water and that's why if you look at the
average human being is the average human being is going to be roughly depends on how much how hot well hydrated you are in your stage of development.

The average human
being is going to be sixty-five percent oxygen by mass. So you are two-thirds oxygen that's because of all of the
water. Water is H2O. And oxygen forms the bulk of the mass of the water molecule. But in second place comes carbon. In
second place comes carbon. Carbon is approximately 18 % of your body's mass. And this is because everything, but the
non fluid ,the non liquid part of your body. In there's a lot of carbon going on there. This right over is a DNA molecule and so these little grey areas, this is
all carbon. This right over here, this right over
here is Hexokinase. I'm not going to go
into the details about what it does. But Hexokinas is a protein. Hexokinas and the teal colored that you see there, that is all carbon. That's all carbon.
This right over here is glucose. It is very sweet.It's an important way to regulate your body's energy.

And the teal color that is carbon. This
is ATP, often considered to be the the molecular currency of the energy in
your body. And all the teal there this is carbon. This is why a lot, especially the non water part
of your body is carbon. So hopefully this gives you a
better appreciation for carbon. It's not just useful for
pencils and diamonds, but even if you're just looking at your hand You're looking at a lot of carbon.

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