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Chapter 9

Chapter 9 . Bonding. Hybridization. Hybridization is the mixing of native atomic orbitals to form special orbitals for bonding.

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Chapter 9

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  1. Chapter 9 Bonding

  2. Hybridization • Hybridization is the mixing of native atomic orbitals to form special orbitals for bonding. • Methane CH4- The carbon has a 2s and 2p(x,y,z) orbital filled with valence electrons. These should theoretically make 90 degree bonds with hydrogen but we find them to be 109.5 degrees. • This means that the 2s and 2p (x,y,z) orbitals combine to create the 4 new hybridized orbitals called sp3. • This gives us the tetrahedral shape. • We say the carbon atom undergoes sp3 hybridization or is sp3 hybridized.

  3. sp3 In terms of energy 2p Hybridization Energy 2s

  4. sp2 Hybridization • Ethylene (C2H4) • Double bond acts as a single pair (chapter 8). Bond angles of 120 degrees. • 2s and 2p combined to form 3 sp2 orbital. Third p orbital is perpendicular to each hybridized orbital. • The 3 sp2 orbitals on each carbon are used to share an electron centered on a line running between atoms. This is known as a sigma (σ) bond. • The second part of the double bond results from sharing electrons in the space above and below the sigma bond. This uses the 3 perpendicular p orbital. This is known as a pi (π) bond.

  5. sp Hybridization • CO2 • Involves one s and one p orbital to create two sp hybridized orbitals. • 2p orbital remains unchanged and are used for the 2 pi bonds. • The oxygen atom is sp2 hybridized. • Triple bonds always have 2 pi bonds and 1 sigma bond. • Double bonds always have 1 pi bond and 1 sigma bond.

  6. dsp3 and d2sp3Hybridization • Used when octet rule is exceeded. • dsp3 used when there are five pairs and a trigonalbipyramidal arrangement is needed. • d2sp3 is used when there are six pairs and a octahedral arrangement is needed. • Only sigma bonds no pi bonds.

  7. The Molecular Orbital Model • Atomic orbitals (chapter 7) are replaced by molecular orbitals (MOs). • MOs can hold two electrons with opposite spin. • Orbital properties of interest are size, shape, and energy. H2 • MO1 and MO2 created by the two hydrogen atoms. • MO1 greatest probability is between nuclei, MO2 is on either side of the nuclei. This is called a sigma molecular orbital.

  8. In the molecule only the molecular orbitals exist, the atomic orbitals are gone MO1 is lower in energy than the 1s orbitals they came from. This favors molecule formation Called a bonding orbital MO2 is higher in energy This goes against bonding antibonding orbital The Molecular Orbital Model

  9. The Molecular Orbital Model MO2 Energy 1s 1s MO1

  10. We use labels to indicate shapes, and whether the MO’s are bonding or antibonding. MO1 = s1s MO2 = s1s* (* indicates antibonding) Can write them the same way as atomic orbitals H2 = s1s2 Each MO can hold two electrons, but they must have opposite spins Orbitals are conserved. The number of molecular orbitals must equal the number atomic orbitals that are used to make them. The Molecular Orbital Model

  11. H2- s1s* Energy 1s 1s s1s

  12. The difference between the number of bonding electrons and the number of antibonding electrons divided by two Bond Order

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