CID 272

BeschreibungCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic weight of 40.078 g/mol. Calcium is the fifth most abundant dissolved ion in seawater by both molarity and mass, after Na+, Cl-, Mg2+ and SO42-. Calcium metal is quite reactive. It readily forms a white coating of calcium nitride (Ca3N2) in air at room temperature. It reacts with water and the metal burns in air with an orangered flame, forming largely the nitride, but some oxide. In the visible portion of the spectrum of many stars, including the Sun, strong absorption lines of singly ionized calcium ions are evident. Prominent among these are the H line at 3968.5 A ° and the K line at 3933.7 A°of singly ionized calcium, or Ca II. For the Sun, and stars with low temperatures, the prominence of the H and K lines is an indication of strong magnetic activity in the chromosphere. Measurement of periodic variations of these active regions can also be used to deduce the rotational periods of these stars.

OccurrenceCalcium is the fifth most abundant element found in the Earth’s crust. It is not found asa free element, but as calcium compounds (mostly salts and oxides), which are found on alllandmasses of the world as limestone, marble, and chalk. Calcium, particularly as the compound calcium chloride (CaCl2), is found in the oceans to the extent of 0.15%.Calcium is produced by two methods. One method is the electrolysis of calcium chloride(Ca++ + 2Cl- → CaCl2) as the electrolyte at a temperature of 800°C, during which processmetallic calcium cations (Ca++) are deposited at the cathode as elemental calcium metal.Calcium can also be produced through a thermal process under very low pressure (vacuum)in which lime is reduced by using aluminum.In addition to limestone, calcium is also found in other rocks, coral, shells, eggshells, bones,teeth, and stalactites and stalagmites.

HistoryCalcium (Latin word calcis meaning “lime”) was known as early as the first century when the Ancient Romans prepared lime as calcium oxide from limestone and used “slaked lime” as a “whitewash” on various homes and buildings. Literature dating back to 975 AD notes that “Plaster-of-Paris” (calcium sulfate), is useful for setting broken bones. The metal was not isolated until 1808 when Sir Humphrey Davy of England electrolyzed a mixture of lime and mercuric oxide, using then the new “Voltaic Cell” as an energy source. Davy was trying to isolate calcium. When he heard that Swedish chemist Jns Berzelius and his colleague, Pontin, had prepared calcium amalgam by electrolyzing lime in mercury, he set up a similar system and was successful. He worked with electrolysis throughout his life and also discovered/isolated boron, sodium, potassium, magnesium, calcium, strontium and barium. Calcium metal was not available on a large scale until the beginning of the twentieth century.