Matter is anything that has mass and volume, which means it takes up space. Even air is matter: a filled balloon has more mass than an empty one. Mass measures how much matter is in an object, while weight measures the pull of gravity on it. All matter is made of atoms, the building blocks of matter, and there are only 118 known kinds of atoms. A substance made of one kind of atom is an element, and the periodic table lists every element in order of its atomic number.