20
Ca
Calcium
40.078
Calcium (Ca)
Alkaline Earth MetalGroup 2Period 4s-block-block
Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust. The ion Ca2+ is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.
Latin name: Calcium
Atomic Number
20
Atomic Mass
40.078 g/mol
Phase (STP)
Solid
Electron Config.
[Ar] 4s²
General
SymbolCa
Atomic Number20
Atomic Mass40.078 g/mol
CategoryAlkaline Earth Metal
Group2
Period4
Blocks-block
Electron Configuration[Ar] 4s²
Valence Electrons2
ColourSilvery-white
CAS NumberCAS7440-70-2
Physical Properties
Phase (STP)Solid
Density1.54 g/cm³
Melting Point841.85°C · 1547.33°F · 1115.00 K
Boiling Point1483.85°C · 2702.93°F · 1757.00 K
Atomic Properties
Atomic Radius194 pm
Covalent Radius176 pm
Van der Waals Radius231 pm
Electronegativity1 Pauling
Ionization Energy590 kJ/mol
Electron Affinity2.37 kJ/mol
Oxidation States+1, +2
Ion ChargeCa²⁺
Thermodynamic
Molar Heat25.929 J/(mol·K)
Thermal Conductivity200 W/(m·K)
Electromagnetic
Electrical TypeConductor
Crystal Structure
Crystal StructureFace-centered cubic
Mechanical Properties
Mohs Hardness1.75
Abundance
In Universe0.0070%
In Sun0.0007%
In Earth's Crust4.1000%
In Oceans0.0410%
In Humans1.4000%
In Meteorites1.2000%
Discovery & History
Discovery Year1808
Discovered ByHumphry Davy
Isotopes of Calcium
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| Ca-40 | 96.941% | Stable | — |
| Ca-42 | 0.647% | Stable | — |
| Ca-43 | 0.135% | Stable | — |
| Ca-44 | 2.086% | Stable | — |
| Ca-46 | 0.004% | Stable | — |
| Ca-48 | 0.187% | 4.2 × 10¹⁹ years | β⁻β⁻ |