Cerium

Cerium is a chemical element with an atomic number of 58. This means that the nucleus of cerium has 58 protons in it. The atomic mass of cerium is 140.12. The chemical symbol of cerium is Ce and it is a member of the lanthanide group.
Properties.
Cerium is a grey, shiny or lustrous metal. At room temperature cerium is a solid. It melts and becomes a liquid at 798oC and boils and becomes a gas at 3424oC. It burns in air to form a compound with one cerium atom and two oxygen atoms. 0.0046% of the Earth's crust is cerium which means that it is quite common - more common than Tin and Lead and nearly as common as zinc
Discovery.
Cerium was first found in Sweden in 1803 by Berzelius and Hisinger and Klaproth in Germany. Because it is very reactive, it was not purified until 1875 in Washington DC. Cerium was named after the asteroid or minor planet Ceres which was first seen two years earlier in 1801.
Uses.
Cerium is not often used as a metal since it quickly reacts with the air and tarnishes. Its most common use is as the 'flint' in a lighter, because it easily produces a spark when it is struck with another metal. Cerium is sometimes used in alloys because it often makes the alloy more heat resistant. Cerium is also used in special glass, ceramics and self-cleaning ovens.
Oxidation.
Cerium reacts in two ways to produce cerous compounds or salts and ceric compounds. Cerous salts have an oxidation number of 3 and ceric salts have an oxidation of 4.
Isotopes.
Cerium has many isotopes. Four of them are found in nature instead of having to be made, 
Cerium-140 (88.5% of all cerium) and Ce-142 (11.1%) are the most common. The average of the weights of each isotope is what give cerium its atomic mass of 140.12.