Category: Alkaline earth metal
Atomic Number: 20
Period: 4 | Group: 2
Block: s-block
Structural element of bone, shell and cement: calcium is how life learned to build hard things.
| Property | Value |
|---|---|
| Phase at STP | Solid |
| Density | 1.54000000 g/cm³ |
| Melting Point | 1115.00 K (841.85 °C) |
| Boiling Point | 1757.00 K (1483.85 °C) |
| Heat Capacity | N/A |
| Property | Value |
|---|---|
| Atomic Mass | 40.0780 u |
| Electronegativity (Pauling) | 1.00 |
| Oxidation States | +2 |
| Electron Configuration | [Ar] 4s² |
| Discovered By | Unknown |
|---|---|
| Discovery Year | 1808 |
| Named After | Latin calx, "lime" |
Known as lime since antiquity
Calcium compounds have been used for thousands of years: the ancient Egyptians, Greeks and Romans made lime mortar and plaster, and the element's name comes from the Latin calx, meaning lime. Antoine Lavoisier listed lime among the elements in 1789, suspecting that it was the oxide of an unknown metal.
Davy isolates the metal (1808)
In 1808 Humphry Davy in London isolated calcium by electrolysis of a moist mixture of lime and mercuric oxide, which gave a calcium amalgam; distilling off the mercury left the metal. In Stockholm, Jöns Jacob Berzelius and Magnus Martin af Pontin prepared the amalgam the same year.
Pure calcium
Davy obtained only small, impure amounts. Robert Bunsen and Augustus Matthiessen made larger quantities in 1855 by electrolysis of molten calcium chloride. Industrial production began in the early 20th century.
| ISOTOPE | Neutrons | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|---|
| Ca-40 | 20 | 96.941% | Stable | - |
| Ca-41 | 21 | - | 99400 yrs | ε |
| Ca-42 | 22 | 0.647% | Stable | - |
| Ca-43 | 23 | 0.135% | Stable | - |
| Ca-44 | 24 | 2.086% | Stable | - |
| Ca-45 | 25 | - | 162.61 days | β⁻ |
| Ca-46 | 26 | 0.004% | Stable | - |
| Ca-48 | 28 | 0.187% | ~2.9 × 10¹⁹ yrs | 2β⁻, 2β⁻, β⁻ |
Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.
Construction
Most calcium is used as compounds, not as metal. Limestone (calcium carbonate) is the raw material of cement and lime. Heating limestone gives quicklime (calcium oxide), used in steelmaking, water treatment, flue gas cleaning and paper making. Gypsum (calcium sulfate) is made into plaster and plasterboard.
Metallurgy
Steel: calcium is added to molten steel to remove oxygen and sulfur and to control inclusions.
Making other metals: calcium metal reduces the oxides or fluorides of uranium, thorium and some rare earths to the pure metals.
Batteries: lead-calcium alloys form the grids of maintenance-free lead-acid car batteries.
Chemicals and food
Calcium chloride melts ice on roads and keeps down dust on unpaved roads.
Calcium carbonate is a filler in paper, plastics and paint, and an antacid.
Calcium phosphates go into fertilizers and animal feed, and calcium salts are used to fortify foods.
Limestone, gypsum, fluorite
| Earth's Crust | 0.0415000000 ppm |
|---|---|
| Universe | 0.0000700000 % |