A Molecule is a group of two or more atoms covalently bonded together to form a particle that is a separate entity. Molecules do not carry an overall charge and therefore do not conduct electricity. A molecule consisting of a small number of atoms is referred to as a small molecule or simple molecule, e.g. H2O, CO2. Typically these substances have low melting and boiling points. Boiling point increases with increasing relative molecular mass, Mr. Giant molecular structures have covalent bonding extending throughout. Examples are diamond and silicon dioxide. These are very hard substances with high melting and boiling points.
See also Covalent Bonding.