Effects of Radicals - Molecules

Most substance are made from a combination of different kinds of atoms linked together. These combinations of atoms are called molecules and they may be quite small or very large containing a few atoms or many. The molecule of hydrogen consists of two hydrogen atoms linked together. Water consists of an oxygen atom linked to two hydrogen atoms (H2O). Common salt (Nacl) consists of an atom of the metal sodium linked to an atom of the gas chlorine. Other molecules, such as those of proteins or plastics, are very large and may contain hundreds, thousands or even millions of atoms, usually of just a few varieties, all linked together.

Substances made of molecules are called 'compounds' and most of these contain just a few different kinds of atoms. Human beings are made from just over 20 different atoms, but 93.3% of our bodies are made from only four atoms carbon, hydrogen, oxygen and nitrogen.