Magnesium
. Magnesium, symbol Mg, silvery white metallic element that is relatively unreactive. In group 2 (or IIa) of the periodic table (see Periodic Law ), magnesium is one of the alkaline earth metals . The atomic number of magnesium is 12. PROPERTIES AND OCCURRENCE The metal, first isolated by the British chemist Sir Humphry Davy in 1808, is obtained today chiefly by electrolysis of fused magnesium chloride. Magnesium is malleable and ductile when heated. With the exception of beryllium , it is the lightest metal that remains stable under ordinary conditions. The metal is not attacked by oxygen, water, or alkalies at room temperature; it reacts with acids. When heated to about 800° C (about 1472° F), it reacts with oxygen and emits a brilliant white light. Magnesium melts at about 649° C (1200° F), boils at about 1107° C (about 2025° F), and has a specific gravity of 1.74; the atomic weight of magnesium is 24.305. Magnesium ranks sixth in natural abundance among elements in crustal rocks.