Physical Properties of Calcium
Calcium is a silvery-white, soft metal that tarnishes rapidly in air and reacts with water. It is the fifth most abundant element in Earth’s crust. Calcium has a melting point of 842°C and a boiling point of 1484°C. Its density is 1.55 g/cm³. Calcium has a moderate density, approximately 1.54 times that of water. It is less dense than some of the heavier metals but more dense than most non-metals. Calcium metal has good ductility, electrical and thermal conductivity.
Chemical Properties of Calcium
Calcium has the same number of outer electrons as magnesium, both having two, so their chemical properties are very similar. However, calcium has a larger atomic radius, and the nucleus has less attraction to the outermost electrons, making calcium more reactive than magnesium.
Reactivity of Calcium with Oxygen
Calcium is a fairly soft metal with a shiny silver surface when first cut. The surface quickly becomes dull as calcium reacts with oxygen to form a coating of white-gray calcium oxide. This loose oxide layer doesn't prevent the internal metal from being oxidized, so elemental calcium must be stored in a sealed container. Calcium can also burn in the air, producing a brick-red flame. The products are calcium oxide and a small amount of calcium nitride.
2Ca(s) + O₂(g) → 2CaO(s)
3Ca(s) + N₂(g) → Ca₃N₂(s)
Reactivity of Calcium with Nonmetals like Halogens
Calcium reacts more readily with nonmetals like halogens compared to magnesium. Calcium reacts with bromine at room temperature without the need for heating.
Ca(s) + Br₂(g) → CaBr₂(s) Ca(s) + Cl₂(g) → CaCl₂(s)
Reactivity of Calcium with Carbon Dioxide
Due to its strong reducing nature, calcium can react not only with oxygen but also strip oxygen atoms from certain compounds. Calcium metal can burn in carbon dioxide. White, granular calcium oxide is formed, and black carbon is displaced from carbon dioxide.
2Ca(s) + CO₂(g) → 2CaO(s) + C(s)
Reactivity of Calcium with Water and Acids
Calcium can displace hydrogen from acids and water. Calcium's reactivity is higher than that of magnesium, and calcium hydroxide, which is alkaline, dissolves in water. As a result, calcium reacts vigorously with water to produce hydrogen gas, and phenolphthalein indicator shows the solution to be alkaline.
Abundant hydrogen ions in acids are rapidly replaced by calcium, generating hydrogen gas. This reaction is more intense.
Ca(s) + 2H₂O(g) → Ca(OH)₂(aq) + H₂(g)
Ca(s) + 2HCl(g) → CaCl₂(aq) + H₂(g)