⚛️ The atom
Mostly Empty
Everything you’d call solid, like your hand, this screen or a diamond, is almost entirely empty space.
You’ve seen the atom drawn a hundred times.
It’s usually a neat little ball, with the nucleus in the middle and electrons looping close by.
That picture gets the sizes badly wrong.
The setup
The picture in most textbooks
It shows a fat nucleus in the centre with a few electrons whizzing round it close by, like planets round a sun. The sizes are completely wrong. The nucleus should be thousands of times smaller than that, and the electrons much, much further out.
Your turn. Drag the zoom slider below to take that cartoon out to real scale, and watch the “solid ball” fall apart.
Empty space
99.2%
nucleus : atom = 1 : 5
The textbook picture has a fat nucleus with electrons whizzing round close by, and the scale is completely wrong. Keep zooming.
Imagine the nucleus as a marble.
Then the whole atom would be the size of a stadium around it.
Your guess
Where are the electrons, really?
Put that marble on the centre spot of a football stadium. Where do you think the electrons would be? Pick one before you look.
With the marble on the centre spot, the electrons are…
If the nucleus is a marble on the centre spot, the electrons are out in the back-row seats. The hard part to believe is that every seat in between is empty. There isn’t even air in there, and that empty space is most of what an atom is.
The why
Is anything you own actually solid?
Here are three things you’d swear were solid: your own hand, a desk you can knock on, and a diamond, the hardest natural material on Earth. Tap each one to see how much of it is matter and how much is empty space. They all give the same answer, because they’re all made of atoms.
Empty space inside it
…
← every scrap of matter in the whole atom is thinner than that gold line.
Tap one to check it.
If you’re nearly all empty space…
…why don’t you sink straight through the floor?
The why
Solid things push back
You’re 99.9999999999999% empty space, and so is the floor, so why don’t you fall through it? Drag the right-hand atom into the left one, pushing as hard as you like, and see what happens.
Push-back you’re feeling
0: barely touching
The clouds are made of electrons, and electrons push each other apart, like two magnets held the wrong way round. The harder you press, the harder they push back, and they never actually meet. When something feels solid, what you’re feeling is that push, and it’s this force that holds you up off the floor.
Which kind of atom you have comes down to one number.
That number is a simple count.
Change it by one and you get a different substance entirely.
Elements
The number is how many protons
What makes gold different from oxygen, or from you, is one count: how many protons are in the nucleus of each atom. Add and remove protons below and watch the atom turn into a completely different element.
H
Hydrogen
1 proton in the nucleus
It’s the lightest element, and stars are giant balls of it.
So an atom is a marble in a stadium…
…surrounded by empty seats…
…and it keeps its shape because its electrons push back.
If you squeezed all the empty space out of a whole mountain, it would fit in a sugar cube. A neutron star is made of matter squeezed like that, and a spoonful of it weighs billions of tonnes.
Pass it on
Next time someone knocks on a table and calls it solid, try explaining it to them. Take them from the textbook cartoon out to true scale, with the marble on the centre spot, the electrons in the back row and nothing in between. Then ask why the floor still holds them up, and explain that it’s because the electrons push each other apart.