Forming ions

When atoms gain or lose electrons, they become electrically charged. Gaining electrons means that the atom has more electrons than protons causing it to have a net negative charge, whilst losing electrons means the atom has more protons than electrons, causing it to have a net positive charge. Some atoms can gain or lose more than one electron, and thus they may have charges which are multiples of the charge carried by protons or electrons.

Ionic compounds

When metals react with non-metals, the reaction often produces ions. This results from a transfer of electrons from the metal atoms to those of the non-metal. Oppositely charged ions attract one another, and this results in the formation of 'ionic compounds'. The formation of ionic substances can often release large amount of energy and be quite spectacular, such as in fireworks where metals react with oxygen producing showers of coloured sparks. (see also 'Giant ionic structures').

Covalent bonding

Chemical reactions don't always involve the transfer of electrons from one atom to another. It is possible for atoms to share electrons and when this happens strong bonds known as 'covalent bonds' are formed. These bonds are often formed when two non-metallic elements combine together, such as when hydrogen and oxygen react to form water. Whilst the bonds between the atoms are strong, the forces between molecules is relatively weak, resulting in substances which have relatively low melting and boiling points (see 'Molecular structures').

Molecular structures

Molecular structures are those which result from molecules held together by covalent bonds (see 'Covalent bonds'). Although the covalent bonds between the atoms are strong, there are only weak forces between the molecules themselves. This results in substances which are easy to melt or boil. These substances are often gases or low boiling point liquids, such as carbon dioxide or water. If they are solid, they are soft and do not conduct electricity, such as wax or sulphur.