What is matter?

Everything around you — the air, this screen, your own body — is matter: anything that has mass and takes up space. Zoom in far enough and all of it is built from unimaginably tiny building blocks called atoms.

A substance made of just one kind of atom is an element — like pure gold, oxygen, or carbon. There are only about 90 naturally occurring elements, yet they combine to make everything. It is a bit like an alphabet: a handful of letters spells millions of words.

Matter usually shows up in three familiar states. In a solid the particles are locked in place. In a liquid they slide past one another. In a gas they fly apart and fill their container. Heating or cooling moves a substance between these states without changing what its atoms are.