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2. s-Block Elements eLearn.Punjab

2.2.2 Trends in Chemical Properties of Alkaline-Earth Metals

1. The alkaline-earth metals burn in oxygen to form oxides or in the case of
barium, the peroxide. Beryllium is the least reactive metal in the group. It
is resistant to complete oxidation and stable in air at ordinary temperature
but oxidizes rapidly at about 800“C. Therefore beryllium is not tarnished
by atmospheric attack but the metal soon loses the silvery appearance.

2Be(s) + O2 (g) 800C→ 2BeO(s)

When exposed to air magnesium quickly becomes coated with the layer of
MgO.
This layer protects the surface from further corrosion at ordinary
temperature.

2Mg(s) + O2 (g) → 2MgO(s)

When magnesium is burnt in air a small amount of nitride is
also formed along with magnesium oxide: When barium is
heated in air or oxygen at 500 - 600°C, its peroxide is formed.

Ba(s) + O2 (g) 500−600C→ BaO2 (s)

Barium peroxide

2. Hydrides are produced by treating the molten alkaline
earth metals with hydrogen, usually under high pressures.
Magnesium reacts with hydrogen at high pressure and in the
presence of a catalyst (Mgl2) forming magnesium hydride.

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