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The S-Block Elements

Question
CBSEENCH11007094
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Explain: Lithium exhibits anamalous behaviour in the company of alkali metals.
Or
Name the chief factor responsible for the anomalous behaviour of lithium.
Or
List three properties of lithium in which it differs from the rest of the alkali metals.

Solution

Anomalous behaviour of lithium is due to its:
(i) very small size,
(ii) high electronegativity and ionisation energy enthalpy value and
(iii) the absence of d-orbitals in the valence shell of its atom.
Therefore, lithium differs from other members of the family in the following respects:
(i) Lithium is harder than other alkali metals.
(ii) Lithium combines with oxygen to form lithium oxide while other alkali metals form peroxides and superoxides.
(iii) Lithium when heated with ammonia forms imide, Li2NH, while other alkali metals form amides, MNH2 as:
2 Li space plus space NH subscript 3 space space rightwards arrow space space space Li subscript 2 NH space plus space straight H subscript 2 Na space plus space NH subscript 3 space rightwards arrow space space NaNH subscript 2 space plus space 1 half straight H subscript 2
(iv) Lithium hydroxide and lithium carbonate decompose on heating while the hydroxides and carbonates of other alkali metals do not decompose on heating.
2 LiOH space rightwards arrow space space space Li subscript 2 straight O space plus space straight H subscript 2 straight O Li subscript 2 CO subscript 3 space rightwards arrow space space Li subscript 2 straight O space plus space CO subscript 2
(v) Lithium unlike other alkali metals from no ethynide on reaction with ethyne. 
(vi) Lithium nitrate when heated gives lithium oxide, while other alkali metal nitrates decompose to give the corresponding nitrites. 
4 LiNO subscript 3 space space rightwards arrow with space on top space space 2 Li subscript 2 straight O space plus space 4 NO subscript 2 space plus space straight O subscript 2 2 NaNO subscript 3 space rightwards arrow space space space 2 NaNO subscript 2 space plus space straight O subscript 2

Some More Questions From The s-Block Elements Chapter

Group 1 elements are called alkali metals. Why?

Why caesium can be used in photoelectric cell while lithium can not be?

In aqueous solution, Li+ ion has lowest mobility. Why?

Lithium has highest ionisation energy in group 1 elements, yet it is strongest reducing agent. Comment.

The softness of group 1 elements increases down the group with increasing atomic number. Give reason. 

Which is the most reactive alkali metal and why?

Why alkali metals do not form M2+ ions?

Name the radio active element in group 1. How does it resemble with the remaining elements of the group?

Why alkali metals are normally kept in kerosene oil?

Why lithium cannot be stored in kerosene?

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