Calcium

Calcium is the 20th element in the Periodic table of elements and belongs to the Alkaline earth metal category. Calcium is a soft gray alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust. The ion Ca is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass. 
Calcium is reactive and, for a metal, soft. With a bit of effort, it can be cut with a sharp knife. In contact with air, calcium develops a mixed oxide and nitride coating, which protects it from further corrosion. Calcium reacts easily with water and acids and the metal burns brightly in air, forming mainly the nitride.
==History==
Calcium was first isolated by Sir Humphry Davy in 1808 in London. In a lecture to the Royal Society in June 1808, Davy described his experiments that year, which produced tiny amounts of metal, at best. He could not find any way to produce more calcium metal until a letter from Jöns Berzelius in Stockholm pointed him in the right direction.
Davy learned that Berzelius and Magnus Pontin had used a battery to decompose calcium oxide at a mercury electrode and they had obtained an amalgam of mercury and calcium. (Berzelius, the great Swedish chemist, exchanged a great deal of information with Davy. Berzelius had earlier learned from Davy that potassium could be dissolved in mercury to form an amalgam. Berzelius had extended the method.)
Davy made a paste of slaked lime [calcium oxide, slightly moistened to form calcium hydroxide] and red oxide of mercury [mercury (II) oxide].
He made a depression in the paste and placed about 3.5 grams of mercury metal there to act as an electrode. Platinum was used as the counter electrode. Davy carried out the experiment under naptha (a liquid hydrocarbon under which he had found he could safely store potassium and sodium).
When electricity was passed through the paste, a calcium-mercury amalgam formed at the mercury electrode. Davy removed the mercury by distillation to reveal a new element: calcium. Davy used the same procedure to isolate strontium, barium, and magnesium. He named the metal calcium because of its occurrence in calx.
==Uses==
*Calcium forms alloys with aluminum, beryllium, copper, lead, and magnesium.
*It is used in the manufacture of other metals such as uranium and thorium.
*Calcium is used to remove oxygen, sulfur and carbon from alloys.
*Calcium from limestone is a vital component of Portland cement.
*Quicklime(CaO) is used in many applications in the chemical industry, such as treatment of drinking water – especially for water softening and arsenic removal, animal waste and waste-water.
==Videos==
thumb|left|500 px|Small piece of calcium in about 20ml of water
Category:Element