anything that takes up space and has mass, all matter is made up of atoms.

each element is made of only one kind of atom, there are about 120 elements.

the smallest unit of a chemical element.

formed when 2 or more atoms join together. these may be 2 of the same atom or 2 different atoms.

formed when 2 or more different atoms are joined together. note: all compounds are also molecules, but not all molecules are compounds.