Atoms and Molecules

All matter on earth is a mixture of around 100 pure substances, which we call the elements: hydrogen, oxygen, nitrogen, carbon, and so on. An atom is the smallest particle into which an element can be subdivided without losing its characteristic properties. Atoms are very small indeed: several million would fit into the period at the end of this sentence. All atoms are made up of smaller “subatomic” particles, electrons, protons, and neutrons. The different properties of the elements arise from the varying combinations of subatomic particles that make up their atoms, and in particular their quotas of protons and electrons. Hydrogen atoms contain one proton and one electron; oxygen carries 8 of each, and iron 26.