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


(a) Write the formula and describe the structure of a noble gas species which is isostructural with

(i) IBr2-                                                           (ii) BrO3-

(b) Assign reasons for the following :

(i) SF6 is kinetically inert.

(ii) NF3 is an exothermic compound whereas NCl3 is not.

(iii) HCl is a stronger acid than HF though flourine is more electronegative than chlorine.

(a) (i) IBr2- : It has 2 bond pairs and 3 lone pairs. Therefore according to VSEPR theory it should have Linear structure. IBr2- has (7+2×7+1) i.e. 22 valence electrons. No noble gas has 22 electrons 

 The isoelectronic species for IBr2- is XeF2

(ii) BrO3- : It has 3 bond pairs and 1 lone pair of electrons. Therefore according to VSEPR theory it has pyramidal structure.

It has 26 valence electrons i.e. (7+3×6+1=26).

A noble gas having 26 valence electrons is XeO3 (8+3×6=26). Thus XeO3 also has pyramidal structure.

(b) (i) Because SF6 is showing steric hindrance due to 6 (six) fluorine atoms which make it unable to react further with any other atom.

     (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 molecules 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) Because HCl has large size and less bond strength than HF which makes easier liberation of H+.



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