Calcium (symbol Ca) is the chemical element with atomic number 20 on the periodic table, belonging to the alkaline earth metals in group 2 and period 4. It is a soft, silvery metal that is crucial both in geology (rocks and minerals) and in biology (bones, teeth, and cell function).

Basic facts about Ca

  • Symbol: Ca; atomic number: 20; relative atomic mass: about 40.078.
  • Group 2 (alkaline earth metals), period 4, block: s-block.
  • Standard state at room temperature: solid, silvery to dull gray metal.

Position on the periodic table

  • Calcium sits in the second column (group 2) under magnesium and above strontium, reflecting its two valence electrons and typical +2 oxidation state.
  • Its electron configuration is [Ar]4s2[Ar]4s^2[Ar]4s2, which explains its chemistry as a reactive metal forming Ca²⁺ ions.

Key physical properties

  • Melting point: about 842 °C; boiling point: about 1484 °C.
  • Density is roughly 1.54–1.55 g/cm³ at room temperature, making it lighter than many common metals like iron or copper.

Uses and importance

  • Major component of limestone, chalk, and marble in the form of calcium carbonate, and of gypsum in the form of calcium sulfate.
  • Essential for living organisms: needed for strong bones and teeth and for processes like muscle contraction and nerve signaling in humans.

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