Atomic structure

The chemical behaviour of the various elements arises from the difference in the electron configuration of the atoms in their normal electrically-neutral state. Each atom consists of a heavy nucleus with a positive charge produced by a number of protons (a metal's atomic number is equal to the number of protons). The nucleus also contains neutrons that are electrically neutral. Electrons are negatively charged and are the other basic constituent of an atom. They are distributed around the atomic nucleus in shells (sometimes called orbits). The electronic structure of an atom is responsible for its chemical properties. In metals, the electrons are shared between many nuclei, which provide metals with their special characteristics. See 'Metallic Bond'.