0.4 Chemical bonding  (Page 8/9)

A molecule of copper (II) chloride contains the elements copper and chlorine .

The valency of copper is 2, while the valency of chlorine is 1. In a molecule of copper (II) chloride, two atoms of chlorine will combine with one atom of copper.

The chemical formula for copper (II) chloride is therefore:

$\mathrm{CuCl}{}_2$

Potassium iodide contains potassium and iodide ions.

Potassium iodide contains the ions $\mathrm{K}{}^{+}$ ( $\mathrm{valency}=1$ ; $\mathrm{charge}=+1$ ) and $\mathrm{I}{}^{-}$ ( $\mathrm{valency}=1$ ; $\mathrm{charge}=-1$ ). In order to balance the charge in a single molecule, one atom of potassium will be needed for every one atom of iodine.

The chemical formula for potassium iodide is therefore:

$\mathrm{KI}$

Sodium sulphate contains sodium ions and sulphate ions.

$\mathrm{Na}{}^{+}$ (valency = 1; charge = +1) and $\mathrm{SO}{}_4^{2-}$ ( $\mathrm{valency}=2$ ; $\mathrm{charge}=-2$ ).

Two sodium ions will be needed to balance the charge of the sulphate ion. The chemical formula for sodium sulphate is therefore:

$\mathrm{Na}{}_2\mathrm{SO}{}_4$

Calcium hydroxide contains calcium ions and hydroxide ions.

Calcium hydroxide contains the ions ${\mathrm{Ca}}^{2+}$ ( $\mathrm{charge}=+2$ ) and $\mathrm{OH}{}^{-}$ ( $\mathrm{charge}=-1$ ). In order to balance the charge in a single molecule, two hydroxide ions will be needed for every ion of calcium.

The chemical formula for calcium hydroxide is therefore:

$\mathrm{Ca(OH)}{}_2$