Question -
Answer -
Generalcharacteristics of alkaline earth metals are as follows.
(i) The general electronic configurationof alkaline earth metals is [noble gas] ns2.
(ii) These metals lose two electrons to acquirethe nearest noble gas configuration. Therefore, their oxidation state is +2.
(iii)These metals have atomic and ionic radii smallerthan that of alkali metals. Also, when moved down the group, the effectivenuclear charge decreases and this causes an increase in their atomic radii andionic radii.
(iv) Since the alkaline earth metals have largesize, their ionization enthalpies are found to be fairly low. However, theirfirst ionization enthalpies are higher than the corresponding group 1 metals.
(v) These metals are lustrous and silvery whitein appearance. They are relatively less soft as compared to alkali metals.
(vi) Atoms of alkaline earth metals are smallerthan that of alkali metals. Also, they have two valence electrons formingstronger metallic bonds. These two factors cause alkaline earth metals to havehigh melting and boiling points as compared to alkali metals.
(vii) They are highly electropositive innature. This is due to their low ionization enthalpies. Also, theelectropositive character increases on moving down the group from Be to Ba.
(viii) Ca, Sr, and Ba impartcharacteristic colours to flames.
Ca– Brick red
Sr– Crimson red
Ba– Apple green
InBe and Mg, the electrons are too strongly bound to be excited. Hence, these donot impart any colour to the flame.
Thealkaline earth metals are less reactive than alkali metals and their reactivityincreases on moving down the group. Chemical properties of alkaline earthmetals are as follows.
(i) Reaction with air and water: Be and Mgare almost inert to air and water because of the formation of oxide layer ontheir surface.
(a) Powdered Be burns in air to form BeOand Be3N2.
(b) Mg, being more electropositive, burnsin air with a dazzling sparkle to form MgO and Mg3N2.
(c) Ca, Sr, and Ba react readily with airto form respective oxides and nitrides.
(d) Ca, Ba, and Sr react vigorously even withcold water.
(ii) Alkaline earth metals react with halogens athigh temperatures to form halides.
(iii) All the alkaline earthmetals, except Be, react with hydrogen to form hydrides.
(iv) They react readily with acids to form saltsand liberate hydrogen gas.
(v) They are strong reducing agents. However,their reducing power is less than that of alkali metals. As we move down thegroup, the reducing power increases.
(vi) Similar to alkali metals, the alkaline earthmetals also dissolve in liquid ammonia to give deep blue coloured solutions.
