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CHEMICAL BONDING AND MOLECULAR STRUCTURE he VSEPR model used for predicting the geometrical shapes of molecules is based on the assumption that electron pairs repel each other and, therefore, tend to remain as far apart as possible. According to this model, molecular geometry is determined by repulsions between lone pairs and lone pairs;lone pairs and bonding pairs andbonding pairs and bonding pairs he order of these re ulsions being l l l b b b he valence bond (VB) approach to o alent bonding is basi ally on erned with the energeti s of o alent bond formation about whi h the ewis and models are silent asi ally the theory dis usses bond formation in terms of o erla of orbitals or e am le the formation of the mole ule from two hydrogen atoms in ol es the o erla of the s 2 orbitals of the two atoms whi h are singly o u ied It is seen that the otential energy of the system gets lowered as the two atoms ome near to ea h other t the equilibrium inter nu lear distan e bond distan e the energy tou hes a minimum ny attem t to bring the nu lei still loser results in a sudden in rease in energy and onsequent destabili ation of the mole ule e ause of orbital o erla the ele tron density between the nu lei in reases whi h hel s in bringing them loser It is howe er seen that the a tual bond enthal y and bond length alues are not obtained by o erla alone and other ariables ha e to be ta en into account. or e laining the hara teristi sha es of olyatomi mole ules auling introdu ed the concept of hybridisation of atomic orbitals. sp, sp , sp hybridi ations of atomi orbitals of e and are used to e lain the formation and geometri al sha es of mole ules li e e l2 l and 2 hey also e lain the formation of multi le bonds in molecules like C 2 2and C 2 . he molecular orbital (MO) theory describes bonding in terms of the combination and arrangment of atomic orbitals to form molecular orbitals that are associated with the molecule as a whole he number of mole ular orbitals are always equal to the number of atomi orbitals from whi h they are formed onding mole ular orbitals in rease ele tron density between the nu lei and are lower in energy than the indi idual atomi orbitals ntibonding mole ular orbitals ha e a region of ero ele tron density between the nu lei and ha e more energy than the indi idual atomi orbitals he ele troni onfiguration of the mole ules is written by filling ele trons in the mole ular orbitals in the order of in reasing energy le els s in the ase of atoms the auli e lusion rin i le and und s rule are a li able for the filling of mole ular orbitals ole ules are said to be stable if the number of elctrons in bonding molecular orbitals is greater than that in antibonding molecular orbitals. Hydrogen bond is formed when a hydrogen atom finds itself between two highly ele tronegati e atoms su h as and It may be intermole ular e isting between two or more mole ules of the same or different substan es or intramole ular resent within the same mole ule ydrogen bonds ha e a owerful effe t on the stru ture and ro erties of many compounds. EXERCISES lain the formation of a hemi al bond rite ewis dot symbols for atoms of the following elements g a r rite ewis symbols for the following atoms and ions 2– – and ; Al and Al and raw the ewis stru tures for the following mole ules and ions 2− 2 i l e 2,CO ,3 efine o tet rule rite its signifi an e and limitations Reprint 2026-27