Important Notes on p-Block Elements for JEE Main 2015 by ednexa.com

1. p-Block Elements
H3PO4 is tribasic while H3PO3 is dibasic. Explain.
Sol:
(1) In oxoacids (or oxyacids) of phosphorus, P-H bonds being non-polar do
not ionize in aqueous solutions to give H+ and hence do not show any basicity
or acidic character.
(2) H+ ions in oxyacids are obtained only from P-OH bonds since O-H bond
is polar. Hence P-OH bonds cause basicity. Therefore basicity of oxoacids is
equal to number of P-H bonds.
(3) In H3PO4, there are three P-OH bonds hence it is tribasic, while in H3PO3
there are two P-OH bonds hence it is dibasic.
Why does R3P=O exist but R3N=O does not?
Sol:
Since nitrogen does not have vacant d-orbital, it can form pπ-π double bond
but cannot form pπ-dπ double like phosphorus which has vacant d-orbital.
Therefore R3N=O does not exist but R3P=0 exists.
H2S is less acidic than H2Te. Explain.
Sol:
(1) Sulphur is more electronegative than Tellurium.

2. (2) Bond energy of S-H in H2S is (347 kJ mol-1) more than the bond energy of
Te-H (238 kJ mol-1).
(3) Hence H2Te dissociates more giving H+ (or H3O) than H2S in the solution.
Therefore H2S is less acidic than H2Te.
Explain ICI is more reactive than I2.
Sol:
(1) In interhalogen compound ICI, the atoms are bonded by covalent bonds.
(2) The covalent bond between dissimilar atoms, I and CI atoms in ICI is
weaker than between similar atoms in I2.
(3) Therefore bond dissociation enthalpy of ICI bond is less than that of I2
bond.
Therefore ICI is more reactive than I2.
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