Q45 of 50 Page 140

BCl3 exists as monomer whereas AlCl3 is dimerised through halogen bridging. Give reason. Explain the structure of the dimer of AlCl3 also.

BCl3 is in trivalent state and has 6 electrons in its valence shell and need two more electrons to complete the octet. BCl3 act as a lewis acid and NH3 can donate its electron. BCl3readily accepts the lone pair of an electron from NH3 and form BCl3.NH3.

BCl3 + NH3 → BCl3.NH3.



AlCl3 forms a stable molecule by making a Dimer. Aluminium has 6 electrons in the valence shell and need 2 more electrons to complete the octet whereas chlorine has 3 lone pair of electron. Aluminium takes up 1 lone pair and forms Dimer with chlorine.



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43

When an aqueous solution of borax is acidified with hydrochloric acid, a white crystalline solid is formed which is soapy to touch. Is this solid acidic or basic in nature? Explain.

 44

Three pairs of compounds are given below. Identify that compound in each of the pairs which have group 13 element in more stable oxidation state. Give a reason for your choice. State the nature of bonding also.

(i) TlCl3, TlCl


(ii) AlCl3 ,AlCl


(iii) InCl3 ,InCl


 46

Boron fluoride exists as BF3 but boron hydride doesn’t exist as BH3. Give reason. In which form does it exist? Explain its structure

 47

(i) What are silicones? State the uses of silicones.

(ii) What are boranes? Give the chemical equation for the preparation of diborane.