The Molecule

The smallest particle of matter that can exist and still retain its identity, such as water (H2O), is called a molecule. A molecule of water is illustrated in Figure 1. Substances composed of only one type of atom are called elements. But most substances occur in nature as compounds, that is, combinations of two or more types of atoms. It would no longer retain the characteristics of water if it were compounded of one atom of hydrogen and two atoms of oxygen. If a drop of water is divided in two and then divided again and again until it cannot be divided any longer, it will still be water.