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We can use dot and cross diagrams to show how a pair of electrons forms a covalent bond.

Here is the dot and cross diagram for oxygen (O₂), a diatomic molecule. Notice the lone pairs of electrons and the two shared pairs of electrons.

Here are the dot and cross diagrams for some other common molecules.

There are different kinds of covalent bonds:

• a single covalent bond is when two atoms share a single pair of electrons. Represented by a single line (–).
• a double covalent bond is when two atoms share two pairs of electrons. Represented by a double line (＝).
• a triple covalent bond is when two atoms share three pairs of electrons. Represented by a triple line (≡).

The table below shows several molecules with double and triple covalent bonds.