Oxygen differs from the other elements of the group. Compounds of oxygen with metals are more ionic in nature and hydrogen bonding is more important for oxygen compounds. Oxygen is never more than divalent because when it has formed two covalent bonds, there are no low energy orbitals which can be used to form further bonds. However, the elements S, Se, Te and Po have empty d-orbitals which may be used for bonding, and they can form four or six bonds by unpairing electrons. The higher oxidation states become less stable on descending the group.
The bond between S and O, or Se and O, are much shorter than might be expected for a single bond owing to p π –d π interaction between the p–orbital of oxygen and d - orbital of S or Se.
(i) Which of the following statement is incorrect ?
Text Solution
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(i)
It is true because of effective p π -d π overlaping owing to small size of sulphur as compared to
phosphorus and silicon.
They have +V and +III oxidation state.
HNO 3 oxidises sulphur to H 2 SO 4 (+VI) but only oxidises selenium to H 2 SeO 3 (+IV). The higher oxidation states become less stable on descending the group.
In M – O electronegativity difference is large while in X – O, it is comparatively smaller (< 1.4).
M = metal and X = non-metal
(ii) . As bond (H–E) dissociation enthalpy decreases down the group, the acidic character increases from H 2 O to H 2 Te.
Order of thermal stability is H 2 O > H 2 S > H 2 Se > H 2 Te .
H 2 O does not have reducing property and this character increases from H 2 S to H 2 Te.
Water has highest boiling point because of H-bonding and thus the correct order is H 2 S < H 2 Se < H 2 Te < H 2 O.
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