Just How Small is an Atom?

You probably already know everything is made up
of little tiny things called atoms or even that each atom
is made up of even smaller particles called protons, neutrons and electrons. And you’ve probably heard
that atoms are small. But I bet you haven’t ever thought
about how small atoms really are. Well, the answer is
that they are really, really small. So you ask, just how small are atoms? To understand this,
let’s ask this question: How many atoms are in a grapefruit? Well, let’s assume that the grapefruit
is made up of only nitrogen atoms, which isn’t at all true, but there
are nitrogen atoms in a grapefruit. To help you visualize this,
let’s blow up each of the atoms to the size of a blueberry. And then how big
would the grapefruit have to be? It would have to be the same size of
— well, actually, the Earth. That’s crazy! You mean to say that if I filled
the Earth with blueberries, I would have the same number
of nitrogen atoms as a grapefruit? That’s right! So how big is the atom? Well, it’s really, really small! And you know what?
It gets even more crazy. Let’s now look inside of each atom
— and thus the blueberry, right? — What do you see there? In the center of the atom
is something called the nucleus, which contains protons and neutrons, and on the outside, you’d see electrons. So how big is the nucleus? If atoms are like blueberries
in the Earth, how big would the nucleus be? You might remember the old pictures
of the atom from science class, where you saw this tiny dot on the page
with an arrow pointing to the nucleus. Well, those pictures,
they’re not drawn to scale, so they’re kind of wrong. So how big is the nucleus? So if you popped open the blueberry
and were searching for the nucleus … You know what? It would be invisible. It’s too small to see! OK. Let’s blow up the atom —
the blueberry — to the size of a house. So imagine a ball that is as tall
as a two-story house. Let’s look for the nucleus
in the center of the atom. And do you know what?
It would just barely be visible. So to get our minds wrapped
around how big the nucleus is, we need to blow up the blueberry,
up to the size of a football stadium. So imagine a ball the size
of a football stadium, and right smack dab
in the center of the atom, you would find the nucleus,
and you could see it! And it would be the size
of a small marble. And there’s more, if I haven’t
blown your mind by now. Let’s consider the atom some more. It contains protons,
neutrons and electrons. The protons and neutrons
live inside of the nucleus, and contain almost
all of the mass of the atom. Way on the edge are the electrons. So if an atom is like a ball
the size of a football stadium, with the nucleus in the center,
and the electrons on the edge, what is in between the nucleus
and the electrons? Surprisingly, the answer is empty space. (Wind noise) That’s right. Empty! Between the nucleus and the electrons,
there are vast regions of empty space. Now, technically there are
some electromagnetic fields, but in terms of stuff,
matter, it is empty. Remember this vast region of empty space
is inside the blueberry, which is inside the Earth, which really are the atoms
in the grapefruit. OK, one more thing,
if I can even get more bizarre. Since virtually all the mass
of an atom is in the nucleus — now, there is some amount
of mass in the electrons, but most of it is in the nucleus — how dense is the nucleus? Well, the answer is crazy. The density of a typical nucleus is four times 10 to the 17th
kilograms per meter cubed. But that’s hard to visualize.
OK, I’ll put it in English units. 2.5 times 10 to the 16th pounds
per cubic feet. OK, that’s still kind of hard to figure. OK, here’s what I want you to do. Make a box that is one foot
by one foot by one foot. Now let’s go and grab
all of the nuclei from a typical car. Now, cars on average weigh two tons. How many cars’ nuclei would you
have to put into the box to have your one-foot-box have
the same density of the nucleus? Is it one car? Two? How about 100? Nope, nope and nope. The answer is much bigger. It is 6.2 billion. That is almost equal to the number
of people in the Earth. So if everyone in the Earth
owned their own car — and they don’t — (Cars honking) and we put all of those
cars into your box … That would be about
the density of a nucleus. So I’m saying that if you took
every car in the world and put it into your one-foot box, you would have the density of one nucleus. OK, let’s review. The atom is really, really, really small. Think atoms in a grapefruit
like blueberries in the Earth. The nucleus is crazy small. Now look inside the blueberry, and blow it up to the size
of a football stadium, and now the nucleus
is a marble in the middle. The atom is made up
of vast regions of empty space. That’s weird. The nucleus has a crazy-high density. Think of putting all those cars
in your one-foot box. I think I’m tired.


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