CHAPTER 2 Bonding and Molecular Structure 15 ensity hetween the atoms and therefore has a lower density)between the atoms and therefore has a higher energy than the individual AO's.An asterisk indicates antibonding. Head head over 一+ σ) wO-9 ③ CX⊙dX○一∞ aipp) (a)o Bonding d⊙一 ⊙⊙ ④ dCX⊙一 g⊙ CX⊙m⊙X⊙一0OX⊙ o(pp) ()Antibonding Figure 2.2 Two parallel p orbitals overlap side by side to form a pi bond IFig.2.3(a)1 or a bond iFig.2.3(b)1 The bond axis lies in a nodal plane (plane of zero electronic density)perpendicular to the cross-sectional plane of theπbond. Single bor oneand onebond.A triple bond isoneand twobond aaaoehM0 se the lecule.it is best to visualize most of them as being localize between pars of bonding atom.This description of bonding is called linear combination of (LCAO). 一 P y (a)πBonding and (b)n'Antibonding F月gure2.3electron density between the atoms and therefore has a lower energy (greater stability) than the individual AO’s. If AO’s of unlike signs overlap, an antiboding MO* results which has a node (site of zero electron density) between the atoms and therefore has a higher energy than the individual AO’s. An asterisk indicates antibonding. Head-to-head overlap of AO’s gives a sigma (σ) MO—the bonds are called σ bonds, [Fig. 2.2(a)]. The corresponding antibonding MO* is designated σ* [Fig. 2.2(b)]. The imaginary line joining the nuclei of the bonding atoms is the bond axis, whose length is the bond length. CHAPTER 2 Bonding and Molecular Structure 15 Figure 2.2 Two parallel p orbitals overlap side by side to form a pi (π) bond [Fig. 2.3(a)] or a π* bond [Fig. 2.3(b)]. The bond axis lies in a nodal plane (plane of zero electronic density) perpendicular to the cross-sectional plane of the π bond. Single bonds are σ bonds. A double bond is one σ and one π bond. A triple bond is one σ and two π bonds (a πz and a πy , if the triple bond is taken along the x-axis). Although MO’s encompass the entire molecule, it is best to visualize most of them as being localized between pairs of bonding atoms. This description of bonding is called linear combination of atomic orbitals (LCAO). Figure 2.3