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Its compounds were known to the ancients, though their chemistry was unknown until the seventeenth century.
It was isolated by Humphry Davy in 1808 via electrolysis of its oxide, who named the element.
Hypothetical univalent salts of calcium would be stable with respect to their elements, but not to disproportionation to the divalent salts and calcium metal, because the enthalpy of formation of MX Calcium is considered to be an alkaline earth metal, along with these heavier elements and the lighter beryllium and magnesium.
It crystallises in the face-centered cubic arrangement like strontium; above 450 °C, it changes to an anisotropic hexagonal close-packed arrangement like magnesium.
The density of 1.55 g·cm Calcium can be cut with a knife with effort, although it is still harder than lead.
For example, calcium spontaneously reacts with water more quickly than magnesium and less quickly than strontium to produce calcium hydroxide and hydrogen gas.
It also reacts with the oxygen and nitrogen in the air to form a mixture of calcium oxide and calcium nitride.