Chemistry

Metals are very useful. Ores are naturally occurring rocks that contain metal or metal compounds in sufficient amounts to make it worthwhile extracting them: most everyday metals are mixtures called alloys.
Methods of extracting metals

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 become 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 high enough concentration to make it economic to extract the metal.
Ores are mined. They may need to be concentrated before the metal is extracted and purified. The economics of using a particular ore may change over time. For example, as a metal becomes rarer, an ore may be used when it was previously considered too expensive to mine.
Reactivity and extraction method
Metals are produced when metal oxides are reduced (have their oxygen removed). The reduction method depends on the reactivity of the metal. For example, aluminium and other reactive metals are extracted by electrolysis, while iron and other less reactive metals may be extracted by reaction with carbon or carbon monoxide.

Metals (in decreasing order of reactivity)
potassium-
sodium-
calcium-
magnesium-
aluminium-
carbon-
zinc-
iron-
tin-
lead-
hydrogen-
copper-
silver-
gold-
platinum-

The transition metals have these properties in common:
they are metals
they are good conductors of heat and electricity
they can be hammered or bent into shape easily
The transition metals are useful as construction materials. They are also useful for making objects that need to let electricity or heat travel through them easily.

Unlike iron, aluminium and titanium cannot be extracted from their oxides by reduction with carbon. You do not need to know any details of how these metals are extracted, but existing methods are expensive because:
the processes have many stages
large amounts of energy are needed
Recycling
Aluminium is extensively recycled because less energy is needed to produce recycled aluminium than to extract aluminium from its ore. Recycling preserves limited resources and requires less energy, so it causes less damage to the environment.

The properties of a metal are changed by adding other elements to it. 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.

Pure copper, gold, iron and aluminium are too soft for many uses. They are mixed with other similar metals to make them harder for everyday use. For example:
brass, used in electrical fittings, is 70 percent copper and 30 percent zinc
18 carat gold, used in jewellery, is 75 percent gold and 25 percent copper and other metals
duralumin, used in aircraft manufacture, is 96 percent aluminium and 4 percent copper and other metals.