COVALENT BONDING: ORBITALS HYBRIDIZATION (9.1)

HYBRIDIZATION Consider methane,CH 4 C has 4 valence electrons 1s 2 2s 2 2p 2 This suggests that there would be two kinds of C-H bonds: one involving a 2s e - on carbon pairing with the 1s on H and the other involving a 2p e - on carbon pairing with the 1s on H. Expt evidence confirms that the four C-H bonds in CH 4 are identical and that CH 4 is tetrahedral.

Figure 9.1 a & b a) The Lewis Structure of the Methane Molecule b) The Tetrahedral Molecular Geometry of the Methane Molecule

HYBRIDIZATION (2) To resolve this conflict, promote a 2s electron to the empty 2p orbital, then mix or hybridize the 2s (1) and 2p (3) orbitals to form four identical hybrid AOs named sp 3 These hybrid atomic orbitals overlap with the 1s orbital on hydrogen to form the covalent C-H bond (sp 3 – 1s). Hybrids form to minimize total energy.

HYBRIDIZATION (3) Using the VSEPR rules, C has four covalent bonds and has tetrahedral molecular geometry. The H-C-H bond angle = o. This agrees with exptal measurements (4 identical C-H bonds). Hybridization integrates electron configurations with expt measurements. Other hybrids: sp 2 (3 e pairs), sp (2), dsp 3 (5), d 2 sp 3 (6)

Figure 9.24 Relationship of the Number of Effective Pairs, Their Spatial Arrangement, and the Hybrid Orbital Set Required

Figure 9.8 The Hybridization of the s, px, and py Atomic Orbitals Results in the Formation of Three sp 2 Orbtitals Centered in the xy Plane

Figure 9.9 An Orbital Energy- Level Diagram for sp 2 Hybridization

Figure 9.11 The Sigma Bonds in Ethylene

Figure 9.13 (a)The Orbitals Used to Form the Bonds in Ethylene (b) The Lewis Structure for Ethylene

Figure 9.16 The Orbital Energy- Level Diagram for the Formation of sp Hybrid Orbitals on Carbon

Figure 9.20 a-d (a) The sp hybridized N atom (b) The  bonds in the N 2 molecule (c) The two pi bonds in N 2 are formed when electron pairs are shared between two sets of parallel p orbitals (d) The total bonding picture of N 2

Figure 9.21 A Set of dsp 3 Hybrid Orbitals on Phosphorus Atom

Figure 9.23 An Octahedral Set of d 2 sp 3 Orbitals on Sulfur Atom

Figure 9.24 Relationship of the Number of Effective Pairs, Their Spatial Arrangement, and the Hybrid Orbital Set Required

HYBRIDS AND MOLECULAR STRUCTURE Write Lewis structure and use VSEPR method to predict e pair geometry Select hybridization scheme this is consistent with VSEPR prediction (Fig 9.24) Identify orbital overlap Form multiple bonds if needed Determine molecular geometry

HYBRIDS AND MULTIPLE BONDS (1) Use Valence Bond method to determine 3- dimensional structure of hydrocarbons with double and triple bonds (planar) Sigma (  ) or end-to-end orbital overlap bond Pi (  ) or side-by-side orbital overlap bond Geometric isomers (2-butene) Benzene and other aromatic compounds

HYBRIDS AND MULTIPLE BONDS (2) A single bond has one sigma bond. A double bond has one sigma bond and one pi bond. A triple bond has one sigma bond and two pi bonds.