21 Chemistry -- Chemical Bonding and Shapes of Molecules

Lone pairs of electrons present on an atom in any molecule affect its geometry. Explain with an example.

Lone pairs of electrons present on an atom in any molecule affect its geometry. Explain with an example.

If the central atom of a molecule has lone pairs along with bond pair of electrons, the ideal geometry is distorted to give different bond angles than expected to obtain minimum repulsion. This is because lone pair occupies more space around the central atom than the bond pair; since the lone pair is attracted by one atom only while bond pair is shared between two nuclei. Hence, repulsion of electron pairs around the central atom is in the order of  l.p--l.p > l.p--b.p. > b.p--b.p


For example: take NH3. Total e.p. in central atom Nitrogen=4Expected shape                                = Tetrahedral (109.5) Actual shape in nature                    =Distorted Tetrahedral (107.5<109.5)                                                              i.e Trigonal Pyramidal Shape

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