The Nucleus: Crash Course Chemistry #1


Hank does his best to convince us that chemistry is not torture, but is instead the amazing and beautiful science of stuff. Chemistry can tell us how three tiny particles – the proton, neutron and electron – come together in trillions of combinations to form … everything. In this inaugural episode of Crash Course


Transcript Provided by YouTube:

00:00
Hello, I’m Hank Green and I want to teach you chemistry.
00:02
But please, do not run away screaming.
00:05
If you give me five minutes to try to convince you that chemistry is not torture,
00:09
but instead the amazing and beautiful science of stuff,
00:13
and if you give it a chance it will not only blow your mind but also give you a deeper understanding of your world.
00:18
This is just my opinion here,
00:20
but I think that understanding the world leads to greater ability to enjoy the world
00:24
and there’s nothing that helps you understand the world better than chemistry.
00:28
Chemistry holds the secrets to how life first formed, how cancers are cured,
00:32
how iPhones have bigger hard drives than 5 year old laptops,
00:36
and how life on this planet might just be able to continue thriving, even ours, if we play our cards right.
00:43
Chemistry is the science of how three tiny particles, the proton, the neutron, and the electron,
00:48
came together in trillions of combinations to form, get this, everything.
00:55
Now chemistry is a peculiar science,
00:57
sometimes talked about as a bridge between the ultra abstract world of particle physics
01:01
and the more visible sciences like biology.
01:03
But calling chemistry a bridge is like calling Eurasia an island.
01:08
Chemistry has it all, mad scientists, world changing revelations, the practical, the impractical,
01:14
medicine, bombs, food, beauty, destruction, life and death, answers to questions you never knew you had.
01:20
I love chemistry, and I hope I can give you a glimpse into why.
01:25
So today, let’s start out with maybe the biggest idea of all time, and move on from there:
01:31
stuff is made from atoms.
01:34
[Theme Music]
01:44
I know, you aren’t shocked, you aren’t awed, you might not even be paying attention any more,
01:49
but when atomic theory was first proposed, it sounded pretty crazy.
01:53
And yes, we call it ‘Atomic Theory’, using the scientific definition of theory,
01:58
which is “a well-tested set of ideas that explains many disparate observations”,
02:02
not the colloquial definition of theory, which is “a guess.”
02:05
But luckily there’s no-one running around any more saying “atoms are just a theory.”
02:09
But it wasn’t that long ago that people were running around saying that.
02:12
You wanna know who settled it for good? Einstein!
02:15
Atoms had been postulated for a long time by the 20th century,
02:19
but it wasn’t until Einstein mathematically proved the existence of atoms and molecules in 1905
02:25
that the matter was truly settled.
02:26
And you thought Einstein was all about relativity and E=mc2, he also proved atoms exist!
02:32
Here’s how it happened:
02:33
In 1827, a botanist named Robert Brown was looking at pollen grains in water through a microscope
02:39
and he noticed that they jiggled randomly even when there was no movement to cause the jiggling.
02:44
It was a mystery for a long time.
02:47
Until 1905 when Einstein theorized that this phenomenon was caused by
02:51
as-yet-unproven atomic particles actually smacking into the grains of pollen.
02:56
He wrote up some fancy math, showing that his theory predicted this motion almost perfectly,
03:02
and everyone had to concede that yes, tiny discrete bits of matter were indeed smacking into the pollen,
03:08
and thus molecules, and by extension atoms, must exist.
03:12
Today, we remember this botanist and his discovery by calling the motion he observed Brownian motion.
03:18
It’s kinda crazy that every physical thing you’ve ever interacted with is made up of little ball thingies.
03:25
It started with people wondering what would happen if you just kept slicing something in half forever.
03:30
Eventually, and of course it turns out that there’s no knife sharp enough to do this,
03:33
you end up with one, pure, unbreakable bit of that substance.
03:37
The word “atom”, indeed, is from the Greek for “indivisible”,
03:40
though, of course, as we learned in World War II, atoms can be broken as well.
03:45
So all the stuff that we think of as stuff is made of atoms, tiny discrete particles that have specific properties,
03:50
depending on the arrangement of three simple subatomic particles.
03:54
There’s the proton, heavy and positively charged, the neutron, about the same size as the proton but neutral,
04:01
and the electron, which has the same amount of charge as the proton, just opposite,
04:05
and very nearly has no mass at all, about 1800 times less massive than the proton or neutron.
04:11
Protons and neutrons hang out in the nucleus, and thus are the nuclear components or nucleons;
04:16
electrons hang out around the nucleus and are the parts of the atom that do all the interesting chemical stuff.
04:20
But before we get to the chemistry of the electrons, we first have got to understand the properties of the nucleus.
04:26
Okay, this is pretty important, so pay attention here.
04:28
The number of protons in an atom determines what element it is.
04:33
79 protons: always gold. 59 protons: always praseodymium.
04:38
The number of protons in an element is its atomic number.
04:41
It sits right on top of the box in the periodic table because that is the element’s defining trait.
04:45
So an atom of silver with 47 protons in its nucleus is always an atom of silver.
04:51
Depending on what its electrons are doing and what it’s bonded to,
04:53
it might be part of a chemical that’s silver-colored or black or blue or shiny or poisonous or a cure for disease,
04:59
but whatever it is, that atom is still silver and will remain an atom of silver probably forever,
05:06
because that core number is very, very difficult to change.
05:09
Now you might have noticed something weird about silver here:
05:11
it’s chemical symbol, the one- or two-letter short code that tells you what it is, is Ag,
05:17
not Si, which is silicon, or Sv which is perfectly available, but Ag. Why? To torture you? No.
05:26
Silver, of course, because we’ve known about it for a long time, was one of the first elements added to the periodic table,
05:31
and back then it was called “argentum”, Latin for “shiny gray stuff.”
05:35
Also, the root of the word “Argentina”,
05:38
where Spanish explorers heard rumors of mountains made of silver, which of course did not exist.
05:43
The name “Argentina”, just like the chemical symbol “Ag”, stuck,
05:48
despite neither of them being particularly representative of reality. Now, back to science.
05:53
Nuclei, which is the plural of nucleus, are boring.
05:56
They’re thousands of times smaller than the atom as a whole,
05:58
and they mostly just sit around being exactly the same as they were when they were first
06:03
created billions of years ago,
06:05
held together by the strongest of the four fundamental forces of physics, the strong nuclear force.
06:09
The fact that nuclei are so boring is the very reason they’re the defining characteristic of elements.
06:14
While electrons can jump from atom to atom whenever it’s convenient,
06:17
the number of protons is almost always extremely stable.
06:20
So that core of the atom, the nucleus, always comes out of chemical reactions unscathed.
06:25
It’s the bit that we can bump around from reaction to reaction,
06:28
but always remains pure and behaves the same way as any other atom with that number of protons.
06:33
The atomic number is the soul of the atom. It’s what makes it it.
06:37
Neutrons are important too, of course, in their own way, but they don’t change what element an atom is.
06:42
One of the two keys to all things chemical is charge, we’ll discuss that in another episode,
06:48
and since neutrons don’t have any charge, they mostly don’t change the properties of an atom.
06:51
But they are, nonetheless, vital.
06:53
We all know that like charges repel each other. Neutrons serve as a kind of buffer between the protons.
06:59
You couldn’t pack silver’s 47 protons together in the nucleus by themselves.
07:03
They couldn’t handle it; they’d rip themselves apart.
07:06
So nuclei only clump together permanently when the right number of protons and neutrons get together.
07:11
Silver needs about 60 neutrons to space out the 47 protons correctly. But it doesn’t have to be 60.
07:17
In fact, silver nuclei are also very stable with 62 neutrons.
07:20
61 though, that doesn’t work, and the reasons for that, I don’t know, you would have to talk to a nuclear physicist.
07:27
The atomic number of silver doesn’t change as the number of neutrons changes
07:30
because the number of protons stays the same.
07:33
But the relative atomic mass does change.
07:36
Relative atomic mass, which used to be called atomic weight back when I was in school,
07:39
is basically the number of protons plus the number of neutrons averaged across all the silver on Earth.
07:45
Because silver has two different stable isotopes, each with a different number of neutrons,
07:49
its relative atomic mass ends up not being a whole number.
07:52
About 52% of silver has 60 neutrons and about 48% has 62.
07:57
The relative atomic mass, then, ends up being about halfway between 107 and 109, 107.8682.
08:04
You’ll note that I said these two different sorts of silver are called isotopes,
08:08
they have different masses but the same chemical properties,
08:10
and are the same element and so belong in the same place on the periodic table.
08:15
In fact, the word “isotope” means “same place”.
08:18
And different isotopes have different mass numbers.
08:21
The mass number is just the total number of nucleons in the nucleus, which is different from atomic mass.
08:26
It’s simple addition for a single atom, rather than an average of all the relative atomic masses of all the silver atoms on Earth.
08:33
So silver has two stable isotopes, one with a mass number of 107, which we’d call silver-107,
08:39
and one with a mass number of 109, silver-109.
08:42
There’s an easy way to write all this out, of course, to keep your information straight.
08:45
The chemical symbol, with the atomic number or number of protons here,
08:49
the mass number, or number of protons and neutrons here,
08:52
and the charge out here, which tells you by simple addition or subtraction how many electrons there are.
08:57
Finally, before we conclude this first episode of Crash Course Chemistry,
09:01
and thus, our discussion of the atomic nucleus, a note on the pronunciation of “nucleus”.
09:07
You are welcome to say “nuculus”, it is an accepted pronunciation of that word,
09:11
but if you can find it in you, it’s probably best to switch over to “nucleus”, which is, after all, how it’s spelled.
09:17
And that is all for today’s episode of Crash Course Chemistry, if you were paying attention, you now know:
09:21
More about atoms than anyone did in 1900,
09:25
like that they were finally confirmed when Einstein mathematically defined Brownian motion;
09:29
That elements are chemically pure substances,
09:31
and the type of element an atom is is defined by how many protons it has in its nucleus, or its atomic number;
09:38
That neutrons stabilize nuclei for their proton friends;
09:41
That different isotopes of the same element are the reason relative atomic masses are never whole numbers;
09:46
and you know that nuclei are the uninteresting, boring bits of the atom,
09:50
and the electrons are where all the interesting chemical-ly stuff happens.
09:54
Crash Course Chemistry is filmed, edited, and directed by Nick Jenkins,
09:57
Dr. Heiko Langner is our Chemistry consultant, sound design is done by Michael Aranda,
10:02
and our graphics team is Thought Bubble.
10:04
If you have any questions, comments, or ideas on any of this stuff we will endeavor to answer
10:07
them in the comments below.
10:09
Thank you for watching Crash Course Chemistry.


This post was previously published on YouTube.

Photo credit: Screenshot from video.

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