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sir, i am confused regarding the backbonding concept... bcoz it exist in BF3 but not in AlCl3 why...?

sir, i am confused regarding the backbonding concept... bcoz it exist in BF3 but not in AlCl3 why...?

Grade:12th pass

1 Answers

Umakant biswal
5349 Points
7 years ago
in BF3 the central atom B has six bonding electrons and a vacant 2p orbital, each F atom has 3 fulfilled 2p orbitals (lone e-pairs). Back bonding occurs between fulfilled 2p orbital of F and vacant 2p orbital of B to complete the octet of B. Back bonding occurs between the same size of orbitals of small atoms. 3p orbitals of Al and Cl are comparatively larger. So, back bonding doesn't occur in AlCl3. In case of AlCl3, the octet of Al is completed by dimerisation. Here, one of the lone pairs of Cl atom is donated to vacant 3p orbital of Al atom of other AlCl3 molecule..
HOpe it helps 
all the best ..

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