NEET Chemistry The p-Block Elements (XII) Questions Solved


(a) Complete the following chemical equations :

(i) NaOH (aq) Hot and conc.+Cl2g 

(ii) XeF6s+H2Ol 

(b) How would you account for the following ?

(i) The value of electron gain enthalpy with negative sign for sulphur is higher than that for oxygen.

(ii) NF3 is an exothermic compound but NCl3 is endothermic compound.

(iii) CIF3 molecule has a T-shaped structure and not a trigonal planar one.                        5 mark

(a) (i) 6NaOH+3Cl25NaCl+1NaClO3+3H2O

(ii) XeF6s+3H2OlXeO3s+6HFaq

(b) (i) Because of enthalpy of dissociation of S-S bond is higher than O-O bond and the hydration energy of S2- is less than that of O2- ion.

(ii) Due to smaller size of F as compared to Cl, the N-F bond is much stronger than N-Cl bond while bond dissociation energy of F2 is much lower than that of Cl2. Therefore, energy released during the formation of NF3 molecule is more than the energy needed to break N2 and F2 molecules into individual atoms. In other words, formation of NF3 is an exothermic reaction.

The energy released during the formation of NCl3 molecule is less than the energy needed to break N2 and Cl2 molecule into individual atoms. Thus formation of NCl3 is an endothermic  reaction.

(iii) The electronic configuration of Cl is 1s2 2s2 2p6 3s2 3Px2 3Py2 3Pz1. It has only one half filled orbital. But to form three Cl-F bonds, we need three half filled orbitals. To achieve this, one of the 3Py2 electrons gets excited to 3d orbital. The resulting five orbitals of the third shell of Cl in the first excited state undergoes SP3d hybridization to give T-shaped structure to CIF3 molecule. Since Cl does not undergo SP2 hybridization, therefore CIF3 does not have trigonal planar structure.

                                                           5 mark


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