This introductory biology lesson explains that life is fundamentally based on chemistry, specifically the properties of carbon and the various types of chemical bonds (covalent, ionic, and hydrogen) that enable complex organic molecules to form and interact.
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if you're wondering this is how the most
revolutionary course in biology of all
time begins come today to learn about
covalent and ionic and hydrogen bonds
what about electron orbitals and the
octet rule and what does it all have to
do with a madman named gilbert lewis
hello i'm hank i assume you're here
because you're interested in biology and
if you are that makes sense because like
any good fitty sense song biology is
just about sex and not dying everyone
watching this should be interested in
sex and not dying being that you are i
assume a human being i'm going to be
teaching this biology course differently
than most courses you've ever taken in
your life for example i'm not going to
spend the first class talking about how
i'm going to spend the rest of the class
i'm just going to start teaching you
like right about now i might say one
more thing before i start teaching yes i
am going to it's that um if i'm going
too fast for you great thing about
youtube is that you can just rewind
watch stuff over and over again if it's
confusing and hopefully it'll become
less confusing and you're even allowed
to fast forward through the bits that
you already know another tip you can
actually even use the number keys on
your keyboard to move around in the
video and i promise you can do this to
me as much as you want and i'm totally
not gonna mind a great professor of mine
once told me that in order to really
understand any topic you have to
understand a little bit of the level of
complexity just below that topic the
level of complexity just below biology
is chemistry and unless you're a
biochemist in which case you would argue
that it's biochemistry either way we're
gonna have to know a little bit of
chemistry in order to get through
biology and so that my friends is where
we're gonna start i am a collection of
organic molecules called hank green
organic compounds are class of compounds
that contain carbon i say carbon is
small i mean that it's actually you know
as an atom it's a relatively small atom
it has six protons and six neutrons for
a total atomic weight of 12. because of
that carbon doesn't take up a lot of
space and so carbon can form itself into
weird rings and sheets and spirals and
double and even triple bonds it could do
all sorts of things that could never be
accomplished by
more bulky atoms it's basically uh you
know you're you're atomic equivalent of
an olympic gymnast it can only do all of
those wonderful beautiful elegant things
because it's kind of tiny also said that
carbon is kind and that's an interesting
sort of thing to say about an atom it's
not like some other elements that are
just desperately trying to do anything
they can to fill up their electron
orbitals no carbon knows what it's like
to be alone and so it's not all please
i'll do anything for your electrons
needy like fluorine or chlorine or
sodium is elements like chlorine if you
breathe them in they like literally tear
up your insides and sodium sodium is
insane if you if you like put it in
water it explodes carbon though
meh it wants more electrons but it's not
gonna like kill to get them it makes and
breaks bonds like a 13 year old mall rat
and it doesn't even hold a grudge carbon
is also as i mentioned before
a bit of a because it needs four
extra electrons and so it'll bond with
pretty much whoever happens to be nearby
and also because it needs four electrons
it'll bond with two or three or even
four of those things at the same time
and carbon is you know willing and
interested to bond with lots of
different molecules like hydrogen oxygen
phosphorus nitrogen or to other
molecules of carbon it can do this in
infinite configurations allowing it to
be the core atom of complicated
structures that make living things like
ourselves life is entirely based on this
element carbon is the foundation of
biology it's so fundamental that
scientists have a pretty difficult time
even conceiving of life that isn't based
on carbon on its own is an atom with six
protons six neutrons and six electrons
atoms have electron shells and they need
to have these shells filled in order to
be happy fulfilled atoms so carbon has
six total electrons two for the first
shell so it's totally happy and four of
the eight it needs to fill the second
shell carbon forms the type of bond that
we call covalent this is when atoms
actually are sharing electrons with each
other so in the case of methane which is
pretty much the simplest carbon compound
ever carbon is sharing its four
electrons in its outer electron shell
with four atoms of hydrogen hydrogen
atoms only have one electron so they
want their first s orbital filled carbon
shares its four electrons with those
four hydrogens and those four hydrogens
each share one electron with carbon so
everybody's happy in chemistry and
biology this is often represented by
what we call lewis dot structures [Music]
[Music]
good lord i'm in a chair
i'm in a chair and there's a book
uh apparently i have something to tell
you that's in this book
which is a book called lewis
asses and bases
by hank green gilbert lewis the guy who
thought up lewis dot structures was also
the guy behind lewis acids and bases and
he was nominated for the nobel prize
35 times this is more nominations than
anyone else ever in history and the
number of times he won is roughly the
same number of times that everyone else
in the world has won which is zero lewis
disliked this a great deal it's kind of
like a baseball player having more hits
than any other player in history and no
home runs he may have been the most
influential chemist of all time he
coined the term photon he revolutionized
how we think about acids and bases and
he produced the first molecule of heavy
water and he was the first person to
conceptualize the covalent bond that
we're talking about right now gilbert
lewis died alone in his laboratory while
working on cyanide compounds after
having had lunch with a younger more
charismatic colleague who had won the
nobel prize and who had worked on the
manhattan project many suspect that he
killed himself with the cyanide
compounds that he was working on but the
medical examiner said heart attack
without really looking into it i told
you all of that because uh the the
little lewis dot structure that we use
to represent
how uh atoms bond to each other is
something that was created by a troubled
mad genius it's not some abstract
scientific thing that's always existed
it's a tool that was thought up by a guy
and it was so useful that we've been
using it ever since in biology most
compounds can be displayed in lewis dot
structure form and here's how that works
these structures basically show how
atoms bond together to make up molecules
and one of the rules of thumb when
making these diagrams is that the
elements that we're working with here
react with one another in such a way
that each atom ends up with eight
electrons in its outermost shell that is
called the octet rule because atoms want
to complete their octets of electrons to
be happy and satisfied oxygen has six
electrons in its octet and needs two
which is why we get h2o it can also bond
with carbon which needs four so you get
two double bonds to two different oxygen
atoms and you end up with co2 that pesky
global warming gas and also the stuff
that makes all life on earth possible
nitrogen has five electrons in its outer
shell here's how we count them there are
four placeholders each of them wants two
atoms and like people getting on a bus
they prefer to start out not sitting
next to each other i'm not kidding about
this they really don't double up until
they have so for maximum happiness
nitrogen bonds with three hydrogens
forming ammonia or with two hydrogens
sticking off another group of atoms
which we call an amino group and if that
amino group is bonded to a carbon that
is bonded to a carboxylic acid group
then you have an amino acid you've heard
of those right sometimes electrons are
shared equally within a covalent bond
like with o2 that's called a nonpolar
covalent bond but often one of the
participants is more greedy in water for
example the oxygen molecule sucks the
electrons in and they spend more time
with the oxygen than with the hydrogens
this creates a slight positive charge
around the hydrogens and a slight
negative charge around the oxygen when
something has a charge we say that it's
polar it has a positive and negative
pole and so it's a polar covalent bond
now let's talk for a moment about a
completely different type of bond which
is an ionic bond and that's when instead
of sharing electrons atoms just
completely wholeheartedly donate or
accept an electron from another atom and
then live happily as a charged atom and
there actually is no such thing as a
charged atom if an atom has a charge
it's an ion atoms in general prefer to
be neutral but compared with having a
full octet
it's not that big of a deal just like we
often choose between being emotionally
balanced and sexually satisfied atoms
will sometimes make sacrifices for that
octet the most common ionic compound in
our daily lives is uh salt uh sodium
chloride nacl this stuff despite its
deliciousness as i mentioned previously
is made up of two really nasty chemicals
sodium and chlorine chlorine is what we
call a halogen which is an element that
only needs one electron to fulfill its
octet and sodium is an alkaline metal
which means that it only has one
electron in its octet so chlorine and
sodium are so close to being satisfied
that they will happily destroy anything
in their path in order to fulfill their
octet and thus there's actually no
better outcome than just to get chlorine
and sodium together and have them loving
on each other they immediately transfer
their electrons so that sodium doesn't
have its one extra and chlorine fills
its octet they become na plus and cl
minus and are so charged that they stick
together and we call that stickiness an
ionic bond and just like if you have two
really crazy friends it might be good to
get them together so that they'll stop
bothering you same thing works with
sodium and chlorine you get those two
together and they'll bother no one and
suddenly they don't want to destroy they
just want to be delicious chemical
changes like this are a big freaking
deal remember chlorine and sodium just a
second ago were definitely killing you
and now they're tasty now we're coming
to the last bond that we're going to
discuss in our intro to chemistry here
and that's the hydrogen bond
imagine that you remember water i hope
that you didn't forget water since water
is stuck together in a polar covalent
bond the hydrogen bit is positively
charged and the oxygen bit is negatively
charged so when water molecules are
moving around we generally think of them
as a perfect fluid but they actually
stick together a little bit hydrogen
side to oxygen side you can actually see
this with your eyes if you fill up a
glass of water uh too full it will
bubble at the top the
the water will stick together at the top
these relatively weak hydrogen bonds
happen in all sorts of chemical
compounds they don't just happen in
water and they actually play an
extremely important role in proteins
which are the chemicals that pretty much
make up our entire bodies a final thing
to note here is that bonds even covalent
bonds ionic bonds even with their own
class are often much different strengths
and we you know tend to just write them
with a little line but uh that line can
represent a very very strong covalent
bond or a relatively weak covalent bond
sometimes ionic bonds are stronger than
covalent bonds though that's generally
not the case and the strength of
covalent bonds varies wildly how these
bonds are made and broken is intensely
important to life and and to our lives
making and breaking bonds is in fact the
key to life itself and like also the key
to death for example if you were to
ingest some sodium metal keep this in
mind as we move forward through biology
even the sexiest person you have ever
met in your life is just a collection
of organic compounds rambling around and
a sack of water review time now we have
the table of contents what i know is
supposed to come at the beginning of
things but we are revolutionary here
we're doing it different so you can
click on any of the things here and you
can go back and review what you learned
uh or didn't learn and if you have
questions please please please please
please please ask them in the comments
and we'll be down there uh answering
them for you so uh
thank you for joining us it was a
pleasure it was a pleasure working with
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