Class 11 Chemistry The S Block Elements Chemical Properties of alkaline earth metal

Chemical Properties of alkaline earth metal

(i) Reactivity towards air and water

Beryllium and magnesium are kinetically inert to oxygen and water due to an oxide film on their surface.

Powdered beryllium burns brilliantly on ignition in air to give BeO and Be3N2.

Magnesium is more electropositive and burns with dazzling brilliance in air to give MgO and Mg3N2.

Calcium, strontium and barium react with water and air.

 

(ii) Reactivity towards the halogens

They combine with halogen to form halides.

M+ X2 --> MX2

(iii) Reactivity towards hydrogen

Alkaline earth metals elements except beryllium combine with hydrogen upon heating to form their hydrides.

But BeH2 can be prepared by following process too.

2BeCl2 +LiAlH4 --> 2BeH2 +LiCl + AlCl3

(iv) Reactivity towards acids

They readily react with acids liberating dihydrogen.

M +2HCl --> MCl2 + H2

 (vi) Solutions in liquid ammonia

Dissolve in liquid ammonia to give deep blue black solutions forming ammoniated ions.

 M + (x+y) NH3 --> [M (NH3) x] 2+ + 2[e (NH3) y]-

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