Topic 7: Part II – Bonding Orbitals and Covalent Bonding

1. Topic 7: Part II – BondingOrbitals and Covalent Bonding • to explain molecular geometry. • In methane, CH4, the shape s tetrahedral. • The valence electrons of carbon should be two in s, and two in p. • the p orbitals would have to be at right angles. • The atomic orbitals change when making a molecule

2. Hybridization • We blend the s and p orbitals of the valence electrons and end up with the tetrahedral geometry. • We combine one s orbital and 3 p orbitals. • sp3hybridization has tetrahedral geometry.

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

4. How we get to hybridization • We know the geometry from experiment. • We know the orbitals of the atom • hybridizing atomic orbitals can explain the geometry. • So if the geometry requires a tetrahedral shape, it is sp3 hybridized • This includes bent and trigonal pyramidal molecules because one of the sp3 lobes holds the lone pair.

5. C: 2s 2p + 4 x H: 1s The Bonding in Methane C forms 4 bonds to H but . . . Electron configuration of C shows only 2 places to bond How does carbon form 4 bonds? At 109.5o angles? HYBRIDIZATION!

6. C: s p 4 sp3 109.5o + + + Electron density distributed to the corners of a tetrahedron sp3 Hybridization of Atomic Orbitals MIX 4 e- domains 4 atomic orbitals 2s + 2px + 2py + 2pz 4 hybrid atomic orbitals 4 sp3 orbitals with 2e- per orbital yield

7. Electrons From Hydrogen Share With sp3 Electrons Pairs of electrons keeps nuclei from repelling

8. Similar for NH3 8 Electrons in sp3, one is a lone pair

9. sp2 hybridization • C2H4 • Double bond acts as one pair. • trigonal planar • Have to end up with three blended orbitals. • Use one s and two p orbitals to make sp2 orbitals. • Leaves one p orbital perpendicular.

10. 2p sp2 Hybridization In terms of energy 2p Energy 2s

11. Where is the P orbital? • Perpendicular • The overlap of orbitals makes a sigma bond (s bond)

12. Two types of Bonds • Sigma bonds from overlap of orbitals. • Between the atoms. • Pi bond (p bond) above and below atoms • Between adjacent p orbitals. • The two bonds of a double bond.

13. H H C C H H

14. When an sp2 Orbital is Used a p Orbital is Left Over for Pi Bonding

15. sp2 hybridization • When three things come off atom. • trigonal planar • 120º • one s one p bond

16. What about two • When two things come off. • One s and one p hybridize. • linear

17. sp hybridization • End up with two lobes 180º apart. • p orbitals are at right angles • Makes room for two p bonds and two sigma bonds. • A triple bond or two double bonds.

18. 2p sp Hybridization In terms of energy 2p Energy 2s

19. sp Hybrid Orbitals BeCl2 or CO2

20. CO2 • C can make two s and two p • O can make one s and one p O C O

21. Breaking the octet • PCl5 • The model predicts that we must use the d orbitals. • dsp3 hybridization • There is some controversy about how involved the d orbitals are.

22. dsp3 • Trigonalbipyrimidal • has only s bonds. • no p bonds. • basic shape for five things.

23. Hybridization Using d Orbitals PCl5 dsp3 SF6 d2sp3

24. PCl5 Can’t tell the hybridization of Cl Assume sp3 to minimize repulsion of electron pairs.

25. d2sp3 • gets us to six things around • octahedral