kalsíum

Kalsíum is a chemical element with the symbol Ca and atomic number 20. It is an alkaline earth metal in group 2 of the periodic table. In its pure form it is a soft, silvery‑white metal that is highly reactive, especially with water and air. Calcium is the fifth most abundant element by mass in the Earth's crust and occurs widely in minerals such as limestone (calcium carbonate) and gypsum (calcium sulfate).

Calcium is essential for living organisms. In humans, about 1–2% of body mass is calcium, with roughly 99% stored in bones and teeth as calcium phosphate. The calcium ion (Ca2+) is crucial for bone mineralization, muscle contraction, nerve transmission, blood clotting, and enzyme activity. Adequate dietary calcium is important for bone health; intake recommendations vary by country and age.

Production and compounds: Industrially, calcium is obtained from limestone by calcination to produce lime (CaO), which can be hydrated to calcium hydroxide (Ca(OH)2). Elemental calcium is produced by electrolysis of molten calcium chloride. Common calcium compounds include calcium carbonate (CaCO3), calcium hydroxide (Ca(OH)2), and calcium phosphate (Ca3(PO4)2).

Uses: The largest applications are in cement and construction (as CaO/Ca(OH)2) and in metallurgy. Calcium compounds are widely used in construction, papermaking, water treatment, and as dietary supplements.

Safety: Calcium is essential but excessive intake can cause constipation, kidney stones, and may interfere with the absorption of other minerals. Deficiency leads to weakened bones and osteoporosis.