Calcium
alkaline earth metal · period 4 · group 2 (alkaline earth metals) · s-block
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air.
What the numbers say
At standard temperature and pressure Calcium is a solid, sitting in period 4, group 2 of the s-block.
Its melting point of 1115 K (842 °C) is the 57th highest of the 110 elements with a measured value — mid-range among the elements.
At 1.55 g/cm³ it is the 81st densest of 96 elements with a quoted density.
Pauling electronegativity is 1. Paired with oxygen (3.44) that is a difference of 2.44, which puts the bond predominantly ionic — expect a stable oxide ceramic.
In the solid state it takes a face-centered cubic structure — FCC packing gives 12 independent slip systems, which is why FCC metals are the ductile, formable ones.
It is reported in 2 oxidation states (1, 2), which sets how many distinct compounds and phases it can form.
First identified in 1808.
Crystal structure
Solid Calcium adopts a Face-centered Cubic arrangement, in the Cubic (isometric) system — axes a = b = c, angles α = β = γ = 90°. Symmetry controls the anisotropy of stiffness and thermal expansion, and the available slip systems set how far the metal deforms before it fractures.
Crystallographic examples
Calcium or one of its compounds is a textbook example for these crystal systems:
- Orthorhombic — α-S, cementite Fe₃C, aragonite CaCO₃, olivine
- Trigonal (rhombohedral) — α-quartz, calcite CaCO₃, Bi, corundum Al₂O₃
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing Ca — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 8 · M 8 · N 2
Properties
| Atomic number | 20 |
|---|---|
| Atomic mass | 40.0784 u |
| Series | alkaline earth metal |
| Group | 2 |
| Period | 4 |
| Block | s-block |
| Phase at STP | Solid |
| Density | 1.55 g/cm³ |
| Melting point | 1115 K (842 °C) |
| Boiling point | 1757 K (1484 °C) |
| Electronegativity (Pauling) | 1 |
| Electron configuration | [Ar] 4s² |
| Crystal structure | Face-centered Cubic |
| Oxidation states | 1,2 |
| Discovered | 1808 |
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See Ca in context with all 118 elements.
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