CHEMICAL BONDING

IONIC BONDS

Group 0 elements all have a full outer shell. This makes them very unreactive. (They don’t form compounds.)

Group 1 elements (alkali metals) all have one electron in their outer shell. (Click here to see group I)

Group VII elements (halogens) all have seven electrons in their outer shell. (Click here to see group VII)

Sodium is in group I. Chlorine is in group VII.

A sodium atom loses its one outer electron easily.
The chlorine atom gains one outer electron easily.

This makes the sodium positively charged and the chlorine negatively charged.

They attract each other to form an ionic bond.

An ion is an atom which has become charged by either gaining or losing electrons.

An ionic bond is the force of attraction between oppositely charged ions.

(Sodium is a highly reactive metal. Chlorine is a very poisonous green gas. Sodium chloride is table salt – a white crystal.)

Ionic compounds tend to be hard, brittle, crystalline solids.

They conduct electricity when molten or in solution.

COVALENT BONDS

A classic example of a covalent compound is the water molecule (H₂O).

A covalent bond consists of a pair of electrons shared by two atoms.

Oxygen is in group VI. It has six outer electrons.

Hydrogen has only one electron.

Two hydrogen atoms each share their electron with the oxygen atom. The oxygen atom, in turn, shares an electron with each hydrogen atom.

Some of the time, each hydrogen atom will have two electrons (a full outer shell.)

Some of the time, the oxygen atom will have eight outer electrons.

Covalents compounds tend to be gases or liquids or soft solids.

They do not conduct electricity. (Pure water does not conduct electricity.)