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2. s-Block Elements eLearn.Punjab

6. Magnesium is more reactive than beryllium, even though it
is not attacked by cold water. Magnesium reacts slowly with
boiling water and quite rapidly with steam to liberate hydrogen.

Mg(s) + H2O(g) 100 C→ MgO(s) + H2 (g)

Steam
Beryllium does not react with water even at red hot temperature
but remaining alkaline earth metals produce hydroxides with water.

M(s) + 2H2O(l) 100 C→ M(OH)2 (s) + H2 (s)

2.2.3 General Trends in Properties of Compounds of Alkali and Alkaline
Earth metals

i) Oxides

Alkali metal oxides dissolve in water to give strong alkaline solutions.
For example:

Li2O(s) + H2O(l) → 2LiOH (aq)
2Na2O2 (s) + 2H2O(l) → 4NaOH (aq) + O2 (g)

The reaction of an alkali metal oxide with water is an acid-base
reaction and not an oxidation reduction reaction since no element
undergoes a change in its oxidation number. The reaction simply
involves the decomposition of water molecule by an oxide ion.

O2− (aq) + H2O(l) → 2OH− (aq)

The basic character of alkali metal oxides increases down the group.
Potassium superoxide (K02) has a very interesting use in breathing
equipments for mountaineers and in space craft. It has the ability
to absorb carbon dioxide while giving out oxygen at the same time.

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