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A molecule 'AB_(5)' has five bond pairs around the central atom 'A'. If the bond pair of electrons are successively replaced by one, two and three lone pair of electrons, then what would be the preferred shapes of the molecules and how do they differ from actual geometry of AB_(5)? |
Answer» Solution :In `AB_(5)` molecule, central atom A is surrounded by five electron PAIRS and no lone pairs. Hence, the structure is a trigonal bipyramid and as there are no lone pairs, so the structure is not distorted. Here in this structure three bonded atoms OCCUPY equatorial positions of the triangle and other two axial positions (top and bottom) of hte equilateral triangle). When one of the bond pairs is replaced by a lone pair, the preferred position of the lone pair is equatorial and the geometry is distorted trigonal bipyramid because in this structure it experiences less number of REPULSIONS and hence stable. ![]() When two lone pairs are present among five electron pairs allowed the central atom then the molecule experiences three types of repulsions and their order is p - 1. p `gt` 1. p - b. p `gt` b. p - b.p. The structure that has lesser repulsions is ![]() The two lone pairs are separated by maximum bond angle of `120^(@)` and hence, the above structure is most preferred geometry that is T-SHAPE with minimum repulsions. When three bond pairs are replaced by a lone pair, then the preferred geometry is the one where three lone pairs occupy equatorial positions with maximum separation of bond angle and hence the shape is linear. ![]() |
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