# Covalent compounds

A covalent bond is a shared pair of electrons between two non-metal atoms, for example carbon dioxide.

Two atoms sharing a pair of electrons.

A covalent bond happens when the positive nuclei from two different atoms are held together by their common attraction for the shared pair of electrons held between them.

Covalent bonds are strong bonds.

Atoms that share pairs of electrons form molecules. A molecule is a group of atoms held together by covalent bonds. Covalent compounds do not conduct electricity.

Substances that consist of covalent molecules are usually gases or liquids at room temperature.

## Ionic compounds

Ionic bonds are formed between a metal and non-metal, for example, sodium chloride. Outer electrons are transferred from the metal to the non-metal.

Sodium will lose an electron and form a positive ion.

Chlorine will gain an electron and form a negative ion.

The ionic bond is the force of attraction between the oppositely charged ions - a positively charged metal ion and a negatively charged non-metal ion.

For example Magnesium (Mg) has the electron arrangement 2,8,2.

To become stable it must lose its two outer electrons to obtain a full outer energy level.

Atoms are neutral because they have equal numbers of protons and electrons however, when they lose two electrons they are no longer neutral. They change into ions with a two positive charge.

$\begin{array}{l} \,\,Mg \to M{g^{2 + }} + 2{e^ - }\\ 2,8,2\,\,\,\,\,\,\,\,2,8 \end{array}$

Non-metals form negative ions because they gain electrons to become stable.

$\begin{array}{l} \,\,\,\,\,Cl\,\,\,\, + \,\,\,\,\,\,{e^ - } \to C{l^ - }\\ 2,8,7\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2,8,8 \end{array}$

When these two charged particles come together they form an ionic bond because the positive magnesium ion is attracted to the negatively charged chlorine ion.

Ionic compounds form what is known as a lattice structure. This is a regular arrangement of metal and non-metal ions which creates compounds with very high melting points which conduct when molten or in solution but NEVER when solid.

Ionic compounds dissolve in water easily, when they do this their lattice breaks up completely. Therefore they can conduct as their ions are free to move.