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You probably know that all stuff is made up of atoms
and that an atom
is a really, really, really, really tiny particle.
Every atom has a core,
which is made up of at least one
positively charged particle
called a proton,
and in most cases,
some number of neutral particles called neutrons.
That core is surrounded
by negatively charged particles called electrons.
The identity of an atom is determined
only by the number of protons in its nucleus.
Hydrogen is hydrogen because it has just one proton,
carbon is carbon because it has six,
gold is gold because it has 79,
and so on.
Indulge me in a momentary tangent.
How do we know about atomic structure?
We can't see protons, neutrons, or electrons.
So, we do a bunch of experiments
and develop a model for what we think is there.
Then we do some more experiments
and see if they agree with the model.
If they do, great.
If they don't, it might be time for a new model.
We've had lots of very different models for atoms
since Democritus in 400 BC,
and there will almost certainly
be many more to come.
Okay, tangent over.
The cores of atoms tend to stick together,
but electrons are free to move,
and this is why chemists love electrons.
If we could marry them,
we probably would.
But electrons are weird.
They appear to behave either as particles,
like little baseballs,
or as waves, like water waves,
depending on the experiment that we perform.
One of the weirdest things about electrons
is that we can't exactly say where they are.
It's not that we don't have the equipment,
it's that this uncertainty
is part of our model of the electron.
So, we can't pinpoint them, fine.
But we can say there's a certain probability
of finding an electron in a given space
around the nucleus.
And that means that we can ask the following question:
If we drew a shape around the nucleus
such that we would be 95% sure
of finding a given electron within that shape,
what would it look like?
Here are a few of these shapes.
Chemists call them orbitals,
and what each one looks like
depends on, among other things,
how much energy it has.
The more energy an orbital has,
the farther most of its density is
from the nucleus.
By they way, why did we pick 95%
and not 100%?
Well, that's another quirk
of our model of the electron.
Past a certain distance from the nucleus,
the probability of finding an electron
starts to decrease
more or less exponentially,
which means that while it will approach zero,
it'll never actually hit zero.
So, in every atom,
there is some small, but non-zero, probability
that for a very, very short period of time,
one of its electrons
is at the other end of the known universe.
But mostly electrons stay close to their nucleus
as clouds of negative charged density
that shift and move with time.
How electrons from one atom
interact with electrons from another
determines almost everything.
Atoms can give up their electrons,
surrendering them to other atoms,
or they can share electrons.
And the dynamics of this social network
are what make chemistry interesting.
From plain old rocks
to the beautiful complexity of life,
the nature of everything we see,
and even feel
is determined at the atomic level.


【TED-Ed】確率の雲として存在する電子 -- ジョージ・ザイダンとチャールズ・モートン (The uncertain location of electrons - George Zaidan and Charles Morton)

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稲葉白兎 2014 年 11 月 30 日 に公開
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