L2: Covalent Compounds

Objectives

• Use the symbols of the elements and write the formulae of simple compounds

• Deduce the formula of a simple compound from the relative numbers of atoms present

• Deduce the formula of a simple compound from a model or a diagrammatic representation

Covalent compounds of non-metals

Consider the Lewis Dot diagrams of these 3 atoms. The dots represent the number of electrons in their outer shell.

Rather than becoming ions by donating or receiving electrons, non-metals tend to share electrons. This can be represented by Dot-Cross diagrams. Unpaired electrons are shared, and each atom 'feels' like it has a full outer shell

Naming Covalent Compounds

We use prefixes to indicate the number of atoms of each element in the molecule.

Exceptions

• If there is only one atom of the first element, we do not add the prefix “mono-” to that element in the name. It is assumed that there is only one atom of that element e.g. carbon dioxide, carbon monoxide

• If oxygen is in the compound, oxygen is always written second in the name. The only exception is if oxygen is bonded with fluorine (this is an advanced fact, you don’t really need to know it)

• Some common compounds have common names that we use instead, e.g. CH₄ (methane), NH₃ (ammonia), H₂O (water)

Naming Covalent Compounds Quiz