Everything is made of atoms.

An atom is a tiny building block, far too small to see. Your hands, the air, this screen, and the stars are all made of them. Here is what is inside one.

Take a look inside

Three parts, one tiny ball

Every atom is built from just three kinds of particles. Two of them clump together in the middle. The third zooms around the outside.

Proton

Positive charge

Protons live in the middle of the atom, in the nucleus. The number of protons is the atom's ID card. It decides which element the atom is.

Neutron

No charge

Neutrons sit in the nucleus next to the protons. They add weight and help hold the nucleus together, like glue that has no opinion about anything else.

Electron

Negative charge

Electrons are tiny and fast, and they whirl around the outside. Opposite charges attract, so the positive nucleus keeps them from flying away.

An atom is mostly empty space

Picture a football stadium. If the nucleus were a pea in the middle of the field, the electrons would be specks out in the seats. Nearly everything in between is empty.

Hundreds of thousands of atoms could line up across the width of one hair.
Nearly all of an atom's weight is packed into its nucleus.
Atoms are so small that a single drop of water holds more than a billion trillion of them.

Build an atom

Add or remove protons and watch what happens. Change the number of protons and you change the element. Nothing else needs to change.

Hydrogen

Protons

Different atoms, different stuff. Same three ingredients.

The oxygen you breathe and the carbon in a pencil differ only in how many protons, neutrons and electrons they hold. Mix atoms together and you get everything else.

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