BCl_(3)is trigonal planar while AlCl_(3) is tetrahedral in dimeric sta

1.	BCl_(3)is trigonal planar while AlCl_(3) is tetrahedral in dimeric state. Explain .
Answer» Solution :Both `BCl_(3)` and `AlCl_(3)` ar electrondeficientmolecules havingsix electronin the valenceshell of their respective central atoms.To completetheir octets the central atoms in each case can ACCEPTA pair of electronsfrom the chlorineatoms ofanothermoleculeformingdimeticstrcutures. However,because ofsmall size of B, itcannotaccomodatesfour big sized Cl atoms around it.THEREFORE,`BCl_(3)` refers to exact as a monomeric planarmoleculein which B atom is `sp^(2)` HYBRIDIZED. Onthe other HAND, Al because of it BIGGER size can easilyacommdate fourCl atomos around it. As a result, `AlCl_(3)` existsas a dimer.In this dimer, sincethe covalencyof Al has increasedto 4. Therefore, Al is`sp^(3)`- hybridisedand the four Clatoms are held tetrahedrallyaround it. for strucutre.

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