Calcium is the chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust. Calcium is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.Symbol: Ca
Atomic number: 20
Electron configuration: [Ar] 4s2
Discovered: 1808
Atomic mass: 40.078 ± 0.004 u
Discoverer: Humphry Davy