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sp Hybrid Orbitals We assume that the Be orbitals in the Be-F bond are 180  apart.

Hybrid Orbitals. sp Hybrid Orbitals We assume that the Be orbitals in the Be-F bond are 180  apart. We could promote and electron from the 2 s orbital on Be to the 2 p orbital to get two unpaired electrons for bonding. BUT the geometry is still not explained.

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sp Hybrid Orbitals We assume that the Be orbitals in the Be-F bond are 180  apart.

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  1. Hybrid Orbitals • sp Hybrid Orbitals • We assume that the Be orbitals in the Be-F bond are 180 apart. • We could promote and electron from the 2s orbital on Be to the 2p orbital to get two unpaired electrons for bonding. • BUT the geometry is still not explained. • We can solve the problem by allowing the 2s and one 2p orbital on Be to mix or form a hybrid orbital.. • The hybrid orbital comes from an s and a p orbital and is called an sp hybrid orbital. Chapter 9

  2. Hybrid Orbitals • sp Hybrid Orbitals • The lobes of sp hybrid orbitals are 180º apart. Chapter 9

  3. Hybrid Orbitals • sp Hybrid Orbitals • Since only one of the Be 2p orbitals has been used in hybridization, there are two unhybridized p orbitals remaining on Be. Chapter 9

  4. Hybrid Orbitals • sp2 and sp3 Hybrid Orbitals • Important: when we mix n atomic orbitals we must get n hybrid orbitals. • sp2 hybrid orbitals are formed with one s and two p orbitals. (Therefore, there is one unhybridized p orbital remaining.) • The large lobes of sp2 hybrids lie in a trigonal plane. • All molecules with trigonal planar electron pair geometries have sp2 orbitals on the central atom. Chapter 9

  5. Hybrid Orbitals • sp2 and sp3 Hybrid Orbitals • sp3 Hybrid orbitals are formed from one s and three p orbitals. Therefore, there are four large lobes. • Each lobe points towards the vertex of a tetrahedron. • The angle between the large lobs is 109.5. • All molecules with tetrahedral electron pair geometries are sp3 hybridized. Chapter 9

  6. sp2 and sp3 Hybrid Orbitals

  7. Hybrid Orbitals sp2 and sp3 Hybrid Orbitals

  8. Hybrid Orbitals • Hybridization Involving d Orbitals • Since there are only three p-orbitals, trigonal bipyramidal and octahedral electron domain geometries must involve d-orbitals. • Trigonal bipyramidal electron domain geometries require sp3d hybridization. • Octahedral electron domain geometries require sp3d2 hybridization. • Note the electron domain geometry from VSEPR theory determines the hybridization. Chapter 9

  9. Hybrid Orbitals • Summary • Draw the Lewis structure. • Determine the electron domain geometry with VSEPR. • Specify the hybrid orbitals required for the electron pairs based on the electron domain geometry. Chapter 9

  10. Multiple Bonds • -Bonds: electron density lies on the axis between the nuclei. • All single bonds are -bonds. • -Bonds: electron density lies above and below the plane of the nuclei. • A double bond consists of one -bond and one -bond. • A triple bond has one -bond and two -bonds. • Often, the p-orbitals involved in -bonding come from unhybridized orbitals. Chapter 9

  11. Multiple Bonds

  12. Multiple Bonds • Ethylene, C2H4, has: • one - and one -bond; • both C atoms sp2 hybridized; • both C atoms with trigonal planar electron pair and molecular geometries. Chapter 9

  13. Multiple Bonds Chapter 9

  14. Formaldehyde 2 Lone Pairs Sigma bond  bond Chapter 9

  15. Multiple Bonds • Consider acetylene, C2H2 • the electron pair geometry of each C is linear; • therefore, the C atoms are sp hybridized; • the sp hybrid orbitals form the C-C and C-H -bonds; • there are two unhybridized p-orbitals; • both unhybridized p-orbitals form the two -bonds; • one -bond is above and below the plane of the nuclei; • one -bond is in front and behind the plane of the nuclei. Chapter 9

  16. Multiple Bonds • When triple bonds form (e.g. N2) one -bond is always above and below and the other is in front and behind the plane of the nuclei. Chapter 9

  17. Multiple Bonds Chapter 9

  18. Multiple Bonds Chapter 9

  19. Hydrogen Cyanide HCN N C  bond Sigma bond  bond N H C Chapter 9

  20. Multiple Bonds Delocalized p Bonding Chapter 9

  21. Multiple Bonds • Delocalized p Bonding • So far all the bonds we have encountered are localized between two nuclei. • In the case of benzene • there are 6 C-C  bonds, 6 C-H  bonds, • each C atom is sp2 hybridized, • and there are 6 unhybridized p orbitals on each C atom. Chapter 9

  22. Multiple Bonds • Delocalized p Bonding • In benzene there are two options for the 3  bonds • localized between C atoms or • delocalized over the entire ring (i.e. the  electrons are shared by all 6 C atoms). • Experimentally, all C-C bonds are the same length in benzene. • Therefore, all C-C bonds are of the same type (recall single bonds are longer than double bonds). Chapter 9

  23. Multiple Bonds • General Conclusions • Every two atoms share at least 2 electrons. • Two electrons between atoms on the same axis as the nuclei are  bonds. • -Bonds are always localized. • If two atoms share more than one pair of electrons, the second and third pair form -bonds. • When resonance structures are possible, delocalization is also possible. Chapter 9

  24. End of Chapter 9:Molecular Geometry and Bonding Theories Chapter 9

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