Calcium

Calcium 40.078(4)   Ca 20 [Ar] 4s2 2,4,s [ ? ] Alkaline Earth Metal: Properties: Silvery-white, hard metal. Compounds: oxide, carbonate, nitrate, sulfide, chloride, and others Hazard: Reacts violently with water and acids to release explosive hydrogen,

Calcium is a chemical element, having the chemical symbol Ca. Its atomic number (the number of protons) is 20. It has a standard atomic weight of 40.078 g•mol ⁻¹, and is a solid in its elemental form.

Calcium is considered to be a member of the "alkaline earth metal" class of element. At a pressure of 101.325 kPa, it has a boiling point of 1,484 °C, and a melting point of 842 °C.

Calcium is essential for life, particularly in cell physiology, where movement of the calcium ion Ca²⁺ into and out of the cytoplasm functions as a signal for many cellular processes, including neuromuscular contractions. It is also a major material used in mineralization of bones, teeth and shells.