The pBlock Elements - Result Question 6

####7. The tendency of BF3,BCl3 and BBr3 to behave as Lewis acid decreases in the sequence: [2010]

(a) BCl3>BF3>BBr3

(b) BBr3>BCl3>BF3

(c) BBr3>BF3>BCl3

(d) BF3>BCl3>BBr3

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Solution:

  1. (b) In BF3,pp overlap between B and F is maximum due to identical size and energy of p-orbitals, so electron deficiency in boron of BF3 is neutralized partially to the maximum extent by back donation. Also, the tendency to back donate decreases from F to I. So the order will be:

BF3<BCl3<BBr3.



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