Metals

Metals usually conduct heat and electricity, are malleable and ductile, and have high melting and boiling points. Non-metals usually show the opposite pattern, with exceptions such as graphite.

Aluminium is used in aircraft because of low density, in overhead cables because it is light and conducts, and in food containers because its oxide layer resists corrosion.

Copper is used in wiring because it is an excellent conductor and ductile.

An alloy is a mixture of a metal with other elements. Brass contains copper and zinc; stainless steel contains iron with elements such as chromium, nickel and carbon.

Different-sized atoms disturb regular metal layers, making sliding more difficult. Alloys can therefore be harder and stronger than pure metals.

The required order is potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver and gold.

A more reactive metal loses electrons more readily and displaces a less reactive metal from its aqueous ions. Metals above hydrogen react with dilute acids to release hydrogen.

Potassium, sodium and calcium react with cold water; magnesium reacts slowly with cold water but faster with steam. Aluminium appears unreactive because of its protective oxide layer.

Iron rusts only when both oxygen and water are present, forming hydrated iron(III) oxide.

Painting, greasing and plastic coating are barriers that exclude oxygen or water. Galvanising coats iron with zinc and also gives sacrificial protection.

A more reactive attached metal loses electrons instead of iron. This sacrificial metal corrodes even if the coating is scratched.

Metals below carbon can often be extracted from oxides by reduction with carbon or carbon monoxide. Iron is extracted from hematite in a blast furnace.

Coke burns to provide heat and carbon dioxide, which reacts with more coke to make carbon monoxide. Carbon monoxide reduces iron(III) oxide.

Limestone decomposes to calcium oxide, which reacts with silica impurity to form liquid calcium silicate slag.

Aluminium is above carbon, so purified aluminium oxide from bauxite is electrolysed. Molten cryolite lowers the operating temperature by dissolving aluminium oxide.

Al³⁺ gains electrons at the carbon-lined cathode. Oxide ions lose electrons at carbon anodes; the oxygen reacts with carbon, so anodes must be replaced.