Element: The simplest type of substances made up of only one type of atom.

Compound: A substance that contains two or more elements chemically joined together.

Mixture: Different substances in the same space, but not chemically combined in fixed proportions.

Note: elements such as oxygen (O2) are described as diatomic because they contain two atoms.

The full list of elements that are diatomic is:

  • Hydrogen (H2)
  • Nitrogen (N2)
  • Fluorine (F2)
  • Oxygen (O2)
  • Iodine (I2)
  • Chlorine (Cl2)
  • Bromine (Br2)