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CHEMICAL BONDING AND MOLECULAR STRUCTURE number of alen e ele trons or e am le for the CO ion the two negati e harges indicate that there are two additional ele trons than those + ro ided by the neutral atoms or ion one ositi e charge indicates the loss of one electron from the group of neutral atoms. C H molecule 2 4 • nowing the hemi al symbols of the When combining atoms share three ombining atoms and ha ing nowledge electron pairs as in the case of two nitrogen of the skeletal structure of the compound atoms in the N molecule and the two carbon atoms in the ethyne molecule, a nown or guessed intelligently it is easy to distribute the total number of electrons triple bond is formed. as bonding shared pairs between the atoms in proportion to the total bonds. • In general the least ele tronegati e atom occupies the central position in the mole ule ion or e am le in the and 2– N2molecule CO , nitrogen and carbon are the central atoms whereas fluorine and o ygen occupy the terminal positions. • After accounting for the shared pairs of electrons for single bonds, the remaining C H molecule ele tron airs are either utili ed for 2 2 multiple bonding or remain as the lone 4.1.3 Lewis Representation of Simple airs he basi requirement being Molecules (the Lewis Structures) that each bonded atom gets an octet of electrons. The Lewis dot structures provide a picture of bonding in molecules and ions in terms of ewis re resentations of a few mole ules the shared pairs of electrons and the octet ions are gi en in able rule. hile su h a i ture may not e lain the bonding and beha iour of a mole ule Table 4.1 The Lewis Representation of completely, it does help in understanding the Some Molecules formation and properties of a molecule to a large e tent riting of ewis dot stru tures of mole ules is therefore ery useful he ewis dot structures can be written by adopting the following steps: • he total number of ele trons required for writing the structures are obtained by adding the alen e ele trons of the ombining atoms or e am le in the mole ule there are eight alen e ele trons a ailable for bonding from arbon and from the four hydrogen atoms • or anions ea h negati e harge would mean addition of one electron. For cations, ea h ositi e harge would result in * Each H atom attains the configuration of helium subtraction of one electron from the total (a duplet of electrons) Reprint 2026-27