Give equations to show that Na is more reactive than Ca and Au is the least reactive metal.
Answers
Metals, in general, are substances which have high electrical conductivity, high thermal conductivity, and high density. Typically they are malleable and ductile, deforming under stress without cleaving. In terms of optical properties, metals are shiny and lustrous. This article is on reactivity series of metals.
Metals are usually inclined to form cations through electron loss, reacting with oxygen in the air to form oxides over various timescales (iron rusts over years, while potassium burns in seconds). Examples:
4 Na + O2 → 2 Na2O (sodium oxide)
2 Ca + O2 → 2 CaO (calcium oxide)
4 Al + 3 O2 → 2 Al2O3 (aluminium oxide).
The transition metals (such as iron, copper, zinc, and nickel) are slower to oxidize because they form a passive layer of oxide that protects the interior. Others, like palladium, platinum and gold do not react with the atmosphere at all.