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 BCl_{3 } exists as monomer whereas AlCl_{3} is dimerised through halogen bridging. Give reason. Explain the structure of the dimer of AlCl_{3} also.

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BCl_{3 }  has 6 electrons in its valence shell and is in trivalent state. It requires two additional electrons to complete the octet. BCl_{3 } act as a Lewis acid and NH_{3} can donate its electron. Therefore, BCl_{3 } readily accepts the lone pair of an electron from NH_{3} and forms BCl_{3}.NH_{3}.


BCl_{3} + NH_{3} \rightarrow BCl_{3}.NH_{3}

AlCl_{3}  makes a stable molecule by forming a Dimer. Aluminium’s valence shell has 6 electrons and it requires 2 additional electrons for completing the octet. While chlorine has 3 lone pairs of electrons. Therefore, Aluminium takes up 1 lone pair and forms Dimer with chlorine.


 

 

 

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