Metals

Metals are very useful. Ores are naturally occurring rocks that contain metal or metal compounds in sufficient amounts to make it worthwhile extracting them. For example, iron ore is used to make iron and steel. Copper is easily extracted, but ores rich in copper are becoming more difficult to find. Aluminium and titanium are metals with useful properties, but they are expensive to extract. Most everyday metals are mixtures called alloys.

The Earth's crust contains metals and metal compounds such as gold, iron oxide and aluminium oxide, but when found in the Earth these are often mixed with other substances. To be useful, the metals have to be extracted from whatever they are mixed with. A metal ore is a rock containing a metal, or a metal compound, in a high enough concentration to make it economic to extract the metal.

The method used to extract metals from the ore in which they are found depends on their reactivity. For example, reactive metals such as aluminium are extracted by electrolysis, while a less-reactive metal such as iron may be extracted by reduction with carbon or carbon monoxide.

Iron is extracted from iron ore in a huge container called a blast furnace. Iron ores such as haematite contain iron oxide. The oxygen must be removed from the iron oxide to leave the iron behind. Reactions in which oxygen is removed are called reduction reactions.

Pure iron is soft and easily shaped. This is because its atoms are arranged in a regular way that lets layers of atoms slide over each other. Pure iron is too soft for many uses. Iron from the blast furnace is an alloy of about 96 per cent iron with carbon and some other impurities. It is hard, but too brittle for most uses. So, most iron from the blast furnace is converted into steel by removing some of the carbon.

The properties of a metal are changed by including other elements, such as carbon. A mixture of two or more elements, where at least one element is a metal, is called an alloy. Alloys contain atoms of different sizes, which distort the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal.

The transition metals have these properties in common:

• They are metals.
• They form coloured compounds.
• They are good conductors of heat and electricity.
• They can be hammered or bent into shape easily.
• They are less reactive than alkali metals such as sodium, they have higher melting points - but mercury is a liquid at room temperature -and they are hard and tough.
• They have high densities.

Copper is a transition metal. It is soft, easily bent and it is a good conductor of electricity. This makes copper useful for electrical wiring. Copper does not react with water, which makes it useful for plumbing.Copper is purified by electrolysis. Electricity is passed through solutions containing copper compounds, such as copper sulfate - sometimes spelt sulphate. Pure copper forms on the negative electrode. The animation shows how this works, but note that you do not need to know the details of the extraction process for your examination.

We are running out of ores rich in copper. Research is being carried out to find new ways to extract copper from the remaining ores, without harming the environment too much. This research is very important, as traditional mining produces huge open-cast mines, and the remaining ores are low-grade, which means that they contain relatively little copper and produce a lot of waste rock.

Aluminium and titanium are two metals with a low density. This means that they are lightweight for their size. They also have a very thin layer of their oxides on the surface, which stops air and water getting to the metal, so aluminium and titanium resist corrosion. These properties make the two metals very useful.

Aluminium is used for aircraft, trains, overhead power cables, saucepans and cooking foil. Titanium is used for fighter aircraft, artificial hip joints and pipes in nuclear power stations.