Interpreting dot and cross diagrams

Dot and cross diagrams show how electrons are shared in covalent bonds. The table shows dot and cross diagrams for an element, chlorine, and two compounds.

Three substances with their formula, structure and a dot and cross diagram.
Question

Deduce the formula of water using information from the table above.

The dot and cross diagram shows that a water molecule is made up of one oxygen atom joined to two hydrogen atoms, so the formula of water is H2O.

Double and triple bonds

Some molecules contain a double bond, which consists of two shared pairs of electrons. For example, oxygen molecules consist of two oxygen atoms joined together. Oxygen atoms can form two covalent bonds, so to link the two oxygen atoms together, a double bond forms between them.

A nitrogen molecule is made up of two nitrogen atoms joined together. Nitrogen atoms can form three covalent bonds, so a triple bond forms between them. The structure of nitrogen is N≡N, showing that it has three shared pairs of electrons.

Oxygen and nitrogen with their formulas, structures and dot and cross diagrams.
Question

Give the structure of an oxygen molecule, using one line to represent each shared pair of electrons.

O=O