Answer:
Lithium resembles magnesium mainly due
to the similarity in sizes of their atoms (Li = 152pm, Mg = 160 pm) and ions (\[L{{i}^{+}}\]
= 76 pm, \[M{{g}^{2+}}\] = 72 pm).
Both have nearly
same electro negativity.
Some of
chemical similarities are:
(i) Both \[LiOH\]
and \[Mg{{(OH)}_{2}}\] are weak bases. These are decomposed on heating.
\[2LiOH\to L{{i}_{2}}O+{{H}_{2}}O\]
\[Mg{{(OH)}_{2}}\to MgO+{{H}_{2}}O\]
(ii) Both
form ionic nitrides which are decomposed by water.
\[6Li+{{N}_{2}}\to 2L{{i}_{3}}N\]
\[3Mg+{{N}_{2}}\to M{{g}_{3}}{{N}_{2}}\]
\[L{{i}_{3}}N+3{{H}_{2}}O\to 3LiOH+N{{H}_{3}}\]
\[M{{g}_{3}}{{N}_{2}}+6{{H}_{2}}O\to
3Mg{{(OH)}_{2}}+2N{{H}_{3}}\]
(iii) Both
combine with carbon on heating. The carbides yield acetylene on hydrolysis.
\[2Li+2C\to
L{{i}_{2}}{{C}_{2}}\]
\[Mg+2C\to Mg{{C}_{2}}\]
\[L{{i}_{2}}{{C}_{2}}+2{{H}_{2}}O\to
2Li(OH)+{{C}_{2}}{{H}_{2}}\]
\[Mg{{C}_{2}}+2{{H}_{2}}O\to Mg{{(OH)}_{2}}+{{C}_{2}}{{H}_{2}}\]
(iv) Carbonates
of Li and Mg decompose on heating.
\[L{{i}_{2}}C{{O}_{3}}\to L{{i}_{2}}O+C{{O}_{2}}\]
\[MgC{{O}_{3}}\to MgO+C{{O}_{2}}\]
(v)\[LiF,L{{i}_{3}}P{{O}_{4}},L{{i}_{2}}{{C}_{2}}{{O}_{4}}\]and\[L{{i}_{2}}C{{O}_{3}}\]like
the corresponding salts of magnesium are insoluble in water.
(vi) \[LiCl\]like\[MgC{{l}_{2}}\]
is deliquescent. Both arc soluble in alcohol and pyridine. Show covalent
nature.
(vii) The
bicarbonates are not known in solid state but only known in solutions.
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