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Hank: Hello, I'm Hank.
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I assume that you are here
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because you are interested in biology.
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If you are, that makes sense,
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because like any good 50 Cent song,
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Biology is just about sex and not dying,
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and everyone watching this
should be interested in sex
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and not dying, being that you
are, I assume, a human being.
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I'm gonna teach this biology
course a little differently
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than most courses you've ever experienced.
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For example, I'm not going
to spend the first class
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talking about how I'm
going to teach the class.
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I'm just going to start
teaching the class.
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Starting right after this next cut.
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First, I just wanted to say
if I'm going to fast for you,
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the great thing about me
being a video and not a person
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is that you can always go back and
listen to what I've said again.
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I promise I will not mind.
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You are encouraged to do this often.
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A great professor of mine once told me
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that in order to understand any topic,
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you only really need to
understand a bit of the level
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of complexity just below that topic.
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The level of complexity just
below biology is chemistry,
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or if you're a biochemist,
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you would probably argue
that it's biochemistry,
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so we need to know a little
bit more about chemistry,
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and that is where we're gonna start.
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(lively intro music)
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I'm a collection of organic
compounds called Hank Green.
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An organic compound is
more or less any chemical
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that contains carbon,
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and carbon is awesome.
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Why? Lots of reasons.
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I'm gonna give you three.
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First, carbon is small.
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It doesn't have that many
protons and neutrons.
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Almost always 12, rarely
it has some extra neutrons
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making it C-13 or C-14.
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Because of that, carbon does
not take up a lot of space
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and can form itself into elegant shapes.
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It can form rings.
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It can form double or even triple bonds.
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It can form spirals and sheets
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and all kinds of really awesome things
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that bigger molecules
would never manage to do.
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Basically, carbon is
like an olympic gymnast.
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It can only do the remarkable
and beautiful things it can do
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because it's petite.
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Second, carbon is kind.
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It's not like other elements that
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desperately want to gain
or lose or share electrons
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to get the exact number they want.
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No, carbon knows what
it's like to be lonely,
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so it's not all, "I can't
live without your electrons."
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Needy, like chlorine or sodium is.
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This is why chlorine
tears apart your insides
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if you breathe it in gaseous form,
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and why sodium metal, if
ingested, will explode.
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Carbon, though, eh.
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It wants more electrons, but
it's not going to kill for them.
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It's easy to work with.
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It makes and breaks bonds
like a 13-year-old mall rat,
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but it doesn't ever really hold a grudge.
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Third, carbon loves to bond
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because it needs 4 extra electrons,
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so it will bond with whoever
happens to be nearby.
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Usually, it will bond
with 2 or 3 or 4 of them
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at the same time.
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Carbon can bond with lots
of different elements.
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Hydrogen, oxygen, phosphorus, nitrogen,
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and other atoms of carbon.
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It can do this in infinite configurations,
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allowing it to be the core element
of the complicated structures
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that make living things like ourselves.
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Because carbon is small,
kind, and loves to bond,
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life is pretty much built around it.
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Carbon is the foundation of biology.
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So fundamental that
scientists have a hard time
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even conceiving of life
that is not carbon-based.
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Silicon, which is analogous
to carbon in many ways,
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is often cited as a potential element
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for alien life to be based on,
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but it's bulkier, so it doesn't form
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the same elegant shapes as carbon.
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It's also not found in any gases,
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meaning that life would have to be formed
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by eating solid silicon,
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whereas life here on
earth is only possible
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because carbon is constantly
floating around in the air
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in the form of carbon dioxide.
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Carbon, on its own, is
an atom with 6 protons,
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6 electrons, and 6 neutrons.
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Atoms have electron shells,
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and they need or want to
have these shells filled,
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in order to be happy, fulfilled atoms.
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The first electron shell
called the S-orbital
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needs 2 electrons to be full.
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Then there's the 2nd
S-orbital, which also needs 2,
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carbon has this filled as well.
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Then we have the first P-orbital,
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which needs 6 to be full.
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Carbon only has 2 left
over, so it wants 4 more.
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Carbon forms a lot of bonds
that we call "covalent".
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These are bonds where the
atoms actually share electrons,
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so the simplest carbon
compound ever, methane,
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is carbon sharing 4 electrons
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with 4 hydrogen atoms.
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Hydrogen only has 1 electron,
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so it wants its first S-orbital full.
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Carbon shares its 4 electrons
with those 4 hydrogens,
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and those 4 hydrogens each
share 1 electron with carbon,
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so everybody's happy.
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This can all be represented
with what we call
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Lewis dot structures.
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Gilbert Lewis, also the guy
behind Lewis acids and bases,
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was nominated for the Nobel Prize 35 times
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and won none.
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This is more nominations
than anyone else in history,
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and roughly the same number
of wins as everyone else.
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Lewis disliked this a great deal.
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He may have been the most
influential chemist of his time.
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He coined the term photon.
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He revolutionized how we
think about acids and bases.
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He produced the first the
first molecule of heavy water,
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and he was the first
person to conceptualize
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the covalent bond that we're
talking about right now.
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But, he was extremely
difficult to work with.
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He was forced to resign
from many important posts,
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and was also passed up
for the Manhattan Project,
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so while all of his colleagues
worked to save his country,
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Lewis wrote a horrible novel.
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Lewis died alone in his laboratory
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while working on cyanide
compounds after having had lunch
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with a younger, more charismatic colleague
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who had won the Nobel prize
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and worked on the Manhattan Project.
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Many suspect that he killed
himself with the cyanide compounds
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that he was working on,
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but the medical examiner said heart attack
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without really looking into it.
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I told you all that because,
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well, the little Lewis structure
that I'm about to show you
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was created by a deeply troubled genius.
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It's not some abstract scientific
thing that has always existed.
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Someone, somewhere, thought it up,
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and it was such a marvelously useful tool,
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that we've been using it ever since.
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In biology, most compounds can be shown
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in Lewis structure form.
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One of the rules of thumb
when making these diagrams
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is that some elements tend
to react with each other
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in such a way that each atom
ends up with 8 electrons
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in its outermost shell.
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That's called the octet rule,
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because these atoms want to complete
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their octets of electrons
to be happy and satisfied.
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Oxygen has 6 electrons in its outer shell,
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and needs 2, which is why we get H2O.
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It can also bond with
carbon, which needs 4,
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so 2 double bonds to 2
different oxygen atoms,
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you end up with CO2,
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that pesky global warming gas,
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and also the stuff that plants
and, thus, all life are made of.
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Nitrogen has 5 electrons
in its outer shell.
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Here's how we count them.
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There are four placeholders.
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Each wants two atoms,
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and like people getting on a bus,
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they prefer to start out not
sitting next to each other.
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I'm not kidding about this.
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They really don't double
up until they have to.
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We count it out.
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1, 2, 3, 4, 5.
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So, for maximum happiness,
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nitrogen bonds with 3 hydrogens,
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forming ammonia,
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or with 2 hydrogens, sticking
off another group of atoms
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which we call an amino group.
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And if that amino group
is bonded to a carbon
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that is bonded to a carboxylic acid group,
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you have an amino acid.
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Sometimes electrons are shared
equally within a covalent bond
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like with O2.
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That's called a non-polar covalent bond,
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but often one of the
participants is more greedy.
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In water, for example, the oxygen molecule
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sucks the electorns in,
and they spend more time
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around the oxygen than
around the hydrogens.
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This creates a slight positive
charge around the hydrogens
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and a slight negative
charge around the oxygen.
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When something has a charge,
we say that it's polar.
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It has a positive and negative pole.
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This is a polar covalent bond.
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Ionic bonds occur when
instead of sharing electrons,
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atoms just donate or accept an electron
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from another atom completely
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and then live happily as
a charged atom or ion.
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Atoms would, in general,
prefer to be neutral
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but compared with having
the full electron shells
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is not that big of a deal.
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The most common ionic
compound in our daily lives?
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that would be good old table
salt, NaCl, sodium chloride,
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but don't be fooled by its deliciousness.
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Sodium chloride, as I
previously mentioned,
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is made of 2 very nasty elements.
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Chlorine is a halogen,
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or an element that only needs one proton
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to fill its octet,
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while sodium is an alkali metal,
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an element that only has
one electron in its octet.
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They will happily tear
apart any chemical compound
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they come in contact with,
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searching to satisfy the octet rule.
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No better outcome could occur
than sodium meeting chlorine.
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They immediately transfer electrons
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so sodium doesn't have its extra
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and the chlorine fills its octet.
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They become Na+ and Cl-,
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and are so charged that
they stick together,
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and that stickiness is
what we call an ionic bond.
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These chemical changes
are a big deal, remember?
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Sodium and chlorine just
went from being deadly
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to being delicious.
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They're also hydrogen bonds,
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which aren't really bonds, so much.
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So, you remember water?
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I hope you didn't forget about water.
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Water is important.
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Since water is stuck together
with a polar covalent bond,
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the hydrogen bit of it is a
little bit positively-charged
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and the oxygen is a
little negatively-charged.
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When water molecules move around,
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they actually stick together a little bit,
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hydrogen side to oxygen side.
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This kind of bonding happens
in all sorts of molecules,
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particularly in proteins.
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It plays an extremely important role
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in how proteins fold up to do their jobs.
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It's important to note here,
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bonds, even when they're written
with dashes or solid lines,
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or no lines at all, are
not the same strength.
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Sometimes ionic bonds are
stronger than covalent bonds,
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though that's the exception
rather than the rule,
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and covalent bond strength varies hugely.
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The way that those bonds
get made and broken
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is intensely important to how
life and our lives operate.
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Making and breaking bonds
is the key to life itself.
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It's also like if you were
to swallow some sodium metal,
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the key to death.
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Keep all of this in mind as
you move forward in biology.
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Even the hottest person you have ever met
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is just a bunch of
chemicals rambling around
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in a bag of water.
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That, among many other things,
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is what we're gonna talk about next time.