Atoms can bond together in one of four ways.

Ionic bonding

An ionic bond is the attraction between two ions of opposite charges. It is formed when electrons are transferred from one atom to another.

Covalent bonding

A covalent bond is formed when two atoms share a pair of electrons. There are two types of covalent bond.

Normal covalent bond: this is where each atom supplies on electron. It is represented by a short straight line between the two atoms

Dative covalent bond: this is where one of the atoms supplies both the electrons. It is represented by the inclusion of a short arrow which points at the atom providing the electrons.

A covalent bond forms because it is more stable for the electrons to be attracted to two nuclei as opposed to only one nucleus. It is more conducive to think of a covalent bond not as a pair of electrons being shared but as a charged cloud because the electrons are constantly moving around.

Metallic bonding

A metallic bond is an attraction between cations and a mass of electrons. It is formed when atoms lose electrons and then the electrons resulting are attracted to the cations remaining. Metallic bonds occur due to the fact that the electrons are more stable attracted to more than one nucleus. These electrons are not attached to one particular atom and are said to be delocalized.