A metal is an element, compound or alloy that is a good conductor of both electricity and heat. They are generally shiny, malleable and ductile. Some elements and compounds are not classified as metals unless under high pressures when they begin to act as metals.
Metallic substances atoms are closely positioned to neighboring atoms in either two possible arrangements. The first arrangement is body-centered cubic. In this arrangement, each atom is positioned at the center of eight other atoms. The second arrangement is face-centered cubic. In this arrangement, each atom is positioned in the center of six others. These two different arrangements form crystal structures. Structures of metals can change depending on the temperature.
Atoms from metallic substances can lost their outer shell electrons. This results in a free flowing cloud of electrons within their otherwise solid arrangement. It provides the ability of metallic substances to easily transmit heat and electricity. The solid characteristic of metals during this flow of electrons occurring is produced by electrostatic interactions between each atom and the electron cloud. This is called metallic bonding.
Metals are inclined to form cations through electron loss reacting with oxygen in the air to form oxides over various timescales. Transition metals (iron, copper, zinc) are slower to oxidize because they form passivation layers of oxide that protects the interior. Other metals such as palladium, platinum and gold, do not react with the atmosphere at all. This is due to the barrier layer of oxide which is formed on the surface which is impenetrable by further oxygen molecules. This allows those metals to retain their shiny appearance and good conductivity.
Alloys are a mixture of two or more elements, which the main component is a metal. Often pure metals are either to soft, brittle or chemically reactive for practical use. Combining different ratios of metals makes alloys have the desirable properties of the pure metals. Common alloys will incorporate aluminium, titanium, copper and magnesium.