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Question
Discuss the general characteristics and gradation in properties of alkaline earth metals.
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Solution
General characteristics of alkaline earth metals:
(1) They have valence shell electronic configuration of ns2.
(2) They lose two valence electron to form dipositive metal ions. Thus, they attain stable noble gas electronic configuration.
(3) The atomic and ionic radii of alkaline earth metals are smaller than the atomic and ionic radii of alkali metals.
(4) Due to large atomic size, the ionization enthalpy value of alkaline earth metals are very low. The first ionization enthalpy values are higher than those of alkali metals.
(5) They have metallic luster and silvery white appearance. Compared to alkali metals, alkaline earth metals have lower softness.
(6) The atomic size of alkaline earth metals is lower than that of alkali metals. Also the metallic bonds are stronger due to presence of 2 valence electrons. Hence, alkaline earths have higher melting and boiling points than alkali metals.
(7) Due to lower ionization enthalpy values, the alkaline earths are highly electopositive in nature. On moving down the group, the electopositive nature increases from Be to Ba.
(8) With exception of Be and Mg, the alkaline earths (Ca, Sr and Ba) provide characteristic colour to flame. Ca, Sr and Ba provide Brick red, Crimson red and Apple green colour to the flame respectively. Be and Mg cannot be excited in the flame as the electrons are tightly held.
The gradation in properties of alkaline earth metals:
The chemical reactivity of alkaline earth metals is lower than the chemical reactivity of alkali metals. On moving down the group, the chemical reactivity increases.
(1) Reaction with air and water: Be and Mg form an inert layer of oxide on their surface. Hence, they are inert to air and water.
(i) In air, powdered Be burns to form its oxide and nitride.
(ii) Mg burns in air with dazzling spark to form oxide and nitride.
(iii) Ca, Sr and Ba readily react with air to form oxides and nitrides.
(iv) Ca, Sr and Ba vigorously react with cold water.
(2) On reaction with halogen at high temperature, alkaline earths form halides.
(3) On reaction with hydrogen, alkaline earths (except Be) form hydrides.
(4) On reaction with acids, alkaline earths form salts and liberate hydrogen.
(5) They act as strong reducing agents. They are weaker reducing agents than alkali metals. On moving down the group, the reducing ability increases.
(6) They dissolve in liquid ammonia. The solution is deep blue in colour due to presence of ammoniated electrons.
(1) They have valence shell electronic configuration of ns2.
(2) They lose two valence electron to form dipositive metal ions. Thus, they attain stable noble gas electronic configuration.
(3) The atomic and ionic radii of alkaline earth metals are smaller than the atomic and ionic radii of alkali metals.
(4) Due to large atomic size, the ionization enthalpy value of alkaline earth metals are very low. The first ionization enthalpy values are higher than those of alkali metals.
(5) They have metallic luster and silvery white appearance. Compared to alkali metals, alkaline earth metals have lower softness.
(6) The atomic size of alkaline earth metals is lower than that of alkali metals. Also the metallic bonds are stronger due to presence of 2 valence electrons. Hence, alkaline earths have higher melting and boiling points than alkali metals.
(7) Due to lower ionization enthalpy values, the alkaline earths are highly electopositive in nature. On moving down the group, the electopositive nature increases from Be to Ba.
(8) With exception of Be and Mg, the alkaline earths (Ca, Sr and Ba) provide characteristic colour to flame. Ca, Sr and Ba provide Brick red, Crimson red and Apple green colour to the flame respectively. Be and Mg cannot be excited in the flame as the electrons are tightly held.
The gradation in properties of alkaline earth metals:
The chemical reactivity of alkaline earth metals is lower than the chemical reactivity of alkali metals. On moving down the group, the chemical reactivity increases.
(1) Reaction with air and water: Be and Mg form an inert layer of oxide on their surface. Hence, they are inert to air and water.
(i) In air, powdered Be burns to form its oxide and nitride.
(ii) Mg burns in air with dazzling spark to form oxide and nitride.
(iii) Ca, Sr and Ba readily react with air to form oxides and nitrides.
(iv) Ca, Sr and Ba vigorously react with cold water.
(2) On reaction with halogen at high temperature, alkaline earths form halides.
(3) On reaction with hydrogen, alkaline earths (except Be) form hydrides.
(4) On reaction with acids, alkaline earths form salts and liberate hydrogen.
(5) They act as strong reducing agents. They are weaker reducing agents than alkali metals. On moving down the group, the reducing ability increases.
(6) They dissolve in liquid ammonia. The solution is deep blue in colour due to presence of ammoniated electrons.
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