Discuss the general characteristics and gradation in properties
of alkaline earth metals.
General characteristics of alkaline earth
metals are as follows.
(i) The general
electronic configuration of alkaline earth metals is [noble
(ii) These metals
lose two electrons to acquire the nearest noble gas
configuration. Therefore, their oxidation state is +2.
(iii)These metals have atomic and ionic
radii smaller than that of alkali metals. Also, when moved down
the group, the effective nuclear charge decreases and this causes
an increase in their atomic radii and ionic radii.
(iv)Since the alkaline earth metals
have large size, their ionization enthalpies are found to be
fairly low. However, their first ionization enthalpies are higher
than the corresponding group 1 metals.
(v) These metals are lustrous and
silvery white in appearance. They are relatively less soft as
compared to alkali metals.
(vi)Atoms of alkaline earth metals are
smaller than that of alkali metals. Also, they have two valence
electrons forming stronger metallic bonds. These two factors
cause alkaline earth metals to have high melting and boiling
points as compared to alkali metals.
(vii) They are highly electropositive
in nature. This is due to their low ionization enthalpies. Also,
the electropositive character increases on moving down the group
from Be to Ba.
(viii) Ca, Sr, and Ba impart
characteristic colours to flames.
Ca â€“ Brick red
Sr â€“ Crimson red
Ba â€“ Apple green
In Be and Mg, the electrons are too strongly bound to be
excited. Hence, these do not impart any colour to the
The alkaline earth metals are less reactive than
alkali metals and their reactivity increases on
moving down the group. Chemical properties of alkaline earth
metals are as follows.
(i) Reaction with air and water: Be and
Mg are almost inert to air and water because of the formation of
oxide layer on their surface.
(a) Powdered Be burns in air to form
(b) Mg, being more electropositive,
burns in air with a dazzling sparkle to form MgO and
(c) Ca, Sr, and Ba react readily with
air to form respective oxides and nitrides.
(d) Ca, Ba, and Sr
react vigorously even with cold water.
(ii) Alkaline earth metals react with
halogens at high temperatures to form halides.
(iii) All the alkaline earth metals,
except Be, react with hydrogen to form hydrides.
(iv) They react readily with acids to
form salts and liberate hydrogen gas.
(v) They are strong reducing agents.
However, their reducing power is less than that of alkali metals.
As we move down the group, the reducing power increases.
(vi) Similar to alkali metals, the
alkaline earth metals also dissolve in liquid ammonia to give
deep blue coloured solutions.
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