B1 中級 5600 分類 收藏
開始影片後,點擊或框選字幕可以立即查詢單字
字庫載入中…
回報字幕錯誤
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 mad man named Gilbert Lewis?
It's all contained within.
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 50 Cent 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 class.
I'm just going to start teaching you, like right about now.
I may say one more thing before I start teaching.
Yes, I am going to!
It's that: if I’m going too fast for you, the great thing about YouTube is
that you can just rewind.
Watch stuff over and over again if it's confusing.
Hopefully, it will 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 going to 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
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 going to start.
I am a collection of organic molecules called Hank Green.
Organic compounds are a class of compounds that contain carbon.
And carbon is this sexy little minx on the periodic table
that's, you know...
disinterested in monogamy.
A jezebel. Bit of a tramp. Hussy.
When I say carbon is small I mean that it's actually
as an atom, it's a relatively small atom.
It has 6 protons and 6 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 can do all sorts of things that could never be accomplished by more bulky atoms.
It's basically, your atomic equivalent of an olympic gymnast.
It can only do all of those wonderful, beautiful, elegant things because it's kind of tiny.
It's 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 breath them in they like literally tear up your insides
and sodium, sodium is insane if you put it in water it explodes!
Carbon though...
Meh.
It wants more electrons, but it's not gonna 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 tramp, 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 willing and interested to bond with lots of different molecules
like hydrogen, oxygen, phosphorous, 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
because carbon is this perfect mix of small, kind, and a little bit trampy
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.
Life is only possible on earth because carbon is always floating around in our atmosphere
in the form of carbon dioxide.
So it's important to note, when I talk about carbon bonding with other elements
I'm not actually talking about sex, it's just a useful analogy.
Carbon, on it's own, is an atom with 6 protons, 6 neutrons, and 6 electrons.
Atoms, have electron shells, and they need to have these shells filled
in order to be happy, fulfilled atoms.
So carbon, has 6 total electrons, 2 for the first shell
so it's totally happy
and 4 of the 8 it needs to fill the second shell.
Carbon forms a 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 it's 4 electrons, in it's outer electron shell, with 4 atoms of hydrogen.
Hydrogen atoms only have 1 electron, so they want their first S orbital filled.
Carbon shares its 4 electrons with those 4 hydrogens
and those 4 hydrogens each share 1 electron with carbon.
So everybody's happy.
In chemistry and biology this is often represented by what we call Lewis dot structures.
Good lord, I'm in a chair!
I'm in a chair and there's a book.
Apparently I have something to tell you that's in this book.
Which is a book called Lewis: Acids 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 was 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.
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 he was working on
but the medical examiner said heart attack, without really looking into it.
I told you all of that because
the little Lewis dot structure that we use to represent how 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 you're 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 8 electrons in it's outermost shell.
That is called the Octet Rule.
Because atoms want to complete their octets of electrons to be happy and satisfied.
Oxygen has 6 electrons in it's octet and needs 2 which is why we get H2O
It can also bond with carbon
which needs 4.
So you get 2 double bonds to 2 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 5 electrons in its outer shell. Here's how we count them:
There are 4 placeholders. Each of them wants 2 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 to.
So for maximum happiness, nitrogen bonds with 3 hydrogens, forming ammonia.
Or with 2 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 non-polar 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 is actually 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 salt.
Sodium chloride. NaCl.
The stuff, despite it's 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 it's octet.
And sodium is an alkaline metal which means that it only has one electron in it's 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 lovin' on each other.
They immediately transfer their electrons.
So that sodium doesn't have it's one extra, and chlorine fills it's octet.
They become Na+ and Cl- 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 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 charge 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 too full
it will bubble at the top. The water will stick together at the top.
That's the polar covalent bonds sticking the water molecules to each other
so that they don't flow right over the top of the glass.
These relatively weak hydrogen bonds happen in all sorts of chemical compounds
they don't just happen in water. An they actually play an extremely important role in proteins
which are the chemicals that pretty much 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 tend to just write them with a little line
but 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 to our lives. Making and breaking bonds is in fact the key to life itself
and 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 in a sack of water.
Review time!
Now we have the table of contents
Which 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.
Or didn't learn.
And if you have questions please please please please please please please
ask them in the comments and we'll be down there answering them for you.
So thank you for joining us.
It was a pleasure, it was a pleasure working with you today.
提示:點選文章或是影片下面的字幕單字,可以直接快速翻譯喔!

載入中…

That's Why Carbon Is A Tramp: Crash Course Biology #1

5600 分類 收藏
Why Why 發佈於 2013 年 3 月 27 日
看更多推薦影片
  1. 1. 單字查詢

    在字幕上選取單字即可即時查詢單字喔!

  2. 2. 單句重複播放

    可重複聽取一句單句,加強聽力!

  3. 3. 使用快速鍵

    使用影片快速鍵,讓學習更有效率!

  4. 4. 關閉語言字幕

    進階版練習可關閉字幕純聽英文哦!

  5. 5. 內嵌播放器

    可以將英文字幕學習播放器內嵌到部落格等地方喔

  6. 6. 展開播放器

    可隱藏右方全文及字典欄位,觀看影片更舒適!

  1. 英文聽力測驗

    挑戰字幕英文聽力測驗!

  1. 點擊展開筆記本讓你看的更舒服

  1. UrbanDictionary 俚語字典整合查詢。一般字典查詢不到你滿意的解譯,不妨使用「俚語字典」,或許會讓你有滿意的答案喔