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CHEMICAL BONDING AND MOLECULAR STRUCTURE and owell in ro osed a sim le theory result in de iations from idealised sha es and based on the re ulsi e intera tions of the alterations in bond angles in molecules. ele tron airs in the alen e shell of the For the prediction of geometrical shapes atoms It was further de elo ed and redefined of mole ules with the hel of theory by yholm and illes ie it is on enient to di ide mole ules into The main postulates of VSEPR theory are two categories as (i) molecules in which as follows: the central atom has no lone pair and (ii) molecules in which the central atom • he sha e of a mole ule de ends u on the number of alen e shell ele tron airs has one or more lone pairs. bonded or nonbonded around the entral able age shows the atom. arrangement of electron pairs about a • airs of ele trons in the alen e shell re el entral atom without any lone airs and one another since their electron clouds are geometries of some molecules/ions of the type negati ely harged able age shows sha es of some simple molecules and ions in which the central • hese airs of ele trons tend to o u y atom has one or more lone airs able such positions in space that minimise re ulsion and thus ma imise distan e age e lains the reasons for the between them. distortions in the geometry of the molecule. s de i ted in able in the • he alen e shell is ta en as a s here with the electron pairs localising on the om ounds of 2 5 and 6, s heri al surfa e at ma imum distan e the arrangement of electron pairs and the atoms around the entral atom are from one another. linear, trigonal planar, tetrahedral, • A multiple bond is treated as if it is a single electron pair and the two or three electron trigonal-bipyramidal and octahedral, res e ti ely u h arrangement an be seen pairs of a multiple bond are treated as a in the mole ules li e and single super pair. l as de i ted below by their ball and • Where two or more resonance structures 5 5 stick models. an re resent a mole ule the model is applicable to any such structure. The repulsive interaction of electron pairs decrease in the order: one air l one air l one air l ond air b ond air b ond air b Fig. 4.6 The shapes of molecules in which central atom has no lone pair yholm and illes ie refined the model by e laining the im ortant he heory is able to redi t difference between the lone pairs and bonding geometry of a large number of molecules, pairs of electrons. While the lone pairs are especially the compounds of p blo elements localised on the central atom, each bonded accurately. It is also quite successful in pair is shared between two atoms. As a result, determining the geometry quite a urately the lone pair electrons in a molecule occupy e en when the energy differen e between more space as compared to the bonding pairs ossible stru tures is ery small he of ele trons his results in greater re ulsion theoret albasisofthe theoryregarding between lone pairs of electrons as compared the effects of electron pair repulsions on to the lone air bond air and bond air molecular shapes is not clear and continues bond pair repulsions hese re ulsion effe ts to be a subject of doubt and discussion. Reprint 2026-27