Kalciumi

Kalciumi, also known as calcium, is a chemical element with the symbol Ca and atomic number 20. It is an alkaline earth metal and the fifth most abundant element by mass in the Earth's crust. In biology it is the fifth most abundant element in the human body. The term kalciumi is used in some languages to refer to this element.

Physically, calcium is a soft, silvery-gray metal that tarnishes in air to a dull oxide layer and is highly reactive, especially with water. In most compounds it adopts the oxidation state +2, which is the dominant form in minerals and biological systems.

Occurrence and compounds: Calcium occurs primarily in minerals such as calcite [CaCO3], aragonite, gypsum [CaSO4·2H2O], and fluorite [CaF2]. It is present as Ca2+ in seawater and most natural waters. The most abundant isotope is Ca-40.

Production and uses: Commercially, calcium is produced by processing limestone to lime (CaO) and then to Ca(OH)2, or by electrolysis of molten calcium compounds for metallic calcium. Major industrial uses include cement and concrete production, lime for environmental and chemical applications, and as an alloying element in steel. Calcium salts and calcium carbonate are widely used as dietary supplements, food additives, and fillers in paper, plastics, and pharmaceuticals.

Biology and health: Calcium is essential for bone and teeth mineralization, muscle contraction, nerve signaling, and blood clotting. It participates in enzyme activity and intracellular signaling. It is tightly regulated by the parathyroid hormone and vitamin D. Dietary sources include dairy products, leafy greens, and fortified foods. Deficiency can cause rickets or osteomalacia; excessive supplementation can lead to hypercalcemia and kidney stones.

History and etymology: The name derives from Latin calx, meaning lime. Calcium was first isolated in 1808 by Sir Humphry Davy through electrolysis of molten calcium compounds.