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Dr. S. M. Condren Chapter 10 Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals.

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Presentation on theme: "Dr. S. M. Condren Chapter 10 Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals."— Presentation transcript:

1 Dr. S. M. Condren Chapter 10 Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals

2 Dr. S. M. Condren Advanced Theories of Chemical Bonding Atomic Orbitals Molecules

3 Dr. S. M. Condren MOLECULAR ORBITAL THEORY Robert Mullikan ( )Robert Mullikan ( ) valence electrons are delocalizedvalence electrons are delocalized valence electrons are in orbitals (called molecular orbitals) spread over entire molecule.valence electrons are in orbitals (called molecular orbitals) spread over entire molecule. Two Theories of Bonding

4 Dr. S. M. Condren Two Theories of Bonding Linus PaulingVALENCE BOND THEORY Linus Pauling valence electrons are localized between atoms (or are lone pairs).valence electrons are localized between atoms (or are lone pairs). half-filled atomic orbitals overlap to form bonds.half-filled atomic orbitals overlap to form bonds.

5 Dr. S. M. Condren Sigma Bond Formation by Orbital Overlap Two s orbitals overlap

6 Dr. S. M. Condren Two s orbitals overlap Two p orbitals overlap Sigma Bond Formation One s and one p orbital overlap

7 Dr. S. M. Condren Using VB Theory Bonding in BF 3 planar triangle angle = 120 o

8 Dr. S. M. Condren How to account for 3 bonds 120 o apart using a spherical s orbital and p orbitals that are 90 o apart?How to account for 3 bonds 120 o apart using a spherical s orbital and p orbitals that are 90 o apart? Pauling said to modify VB approach withPauling said to modify VB approach with ORBITAL HYBRIDIZATION mix available orbitals to form a new set of orbitals that will give the maximum overlap, in the correct geometry. mix available orbitals to form a new set of orbitals HYBRID ORBITALS that will give the maximum overlap, in the correct geometry. Bonding in BF 3

9 Dr. S. M. Condren Bonding in BF 3 rearrange electronshydridize orbs. unused p orbital three sp 2 hybrid orbitals 2p 2s

10 Dr. S. M. Condren The three hybrid orbitals are made from 1 s orbital and 2 p orbitals 3 sp 2 hybrids. The three hybrid orbitals are made from 1 s orbital and 2 p orbitals 3 sp 2 hybrids. Now we have 3, half-filled HYBRID orbitals that can be used to form B-F sigma bonds.Now we have 3, half-filled HYBRID orbitals that can be used to form B-F sigma bonds. Bonding in BF 3

11 Dr. S. M. Condren An orbital from each F overlaps one of the sp 2 hybrids to form a B-F bond. Bonding in BF 3

12 Dr. S. M. Condren BF 3, Planar Trigonal

13 Dr. S. M. Condren Bonding in CH 4 How do we account for 4 CH sigma bonds 109 o apart? Need to use 4 atomic orbitals s, p x, p y, and p z to form 4 new hybrid orbitals pointing in the correct direction.

14 Dr. S. M. Condren Bonding in CH 4

15 Dr. S. M. Condren Bonding in a Tetrahedron Formation of Hybrid Atomic Orbitals 4 C atomic orbitals hybridize to form four equivalent sp 3 hybrid atomic orbitals.

16 Dr. S. M. Condren

17 Bonding in Glycine

18 Dr. S. M. Condren BONDSSHAPEHYBRID REMAIN 2linear sp2 ps 3trigonal sp 2 1 p planar 4tetrahedral sp 3 none Orbital Hybridization

19 Dr. S. M. Condren Multiple Bonds Consider ethylene, C 2 H 4

20 Dr. S. M. Condren Sigma Bonds in C 2 H 4

21 Dr. S. M. Condren π π Bonding in C 2 H 4 The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the π bond.

22 Dr. S. M. Condren π Bonding in C 2 H 4 The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the π bond.

23 Dr. S. M. Condren Multiple Bonding in C 2 H 4

24 Dr. S. M. Condren and π Bonding in C 2 H 4

25 Dr. S. M. Condren and π Bonding in CH 2 O

26 Dr. S. M. Condren and π Bonding in C 2 H 2

27 Dr. S. M. Condren and π Bonding in C 2 H 2

28 Dr. S. M. Condren Consequences of Multiple Bonding There is restricted rotation around C=C bond.

29 Dr. S. M. Condren Consequences of Multiple Bonding Restricted rotation around C=C bond.

30 Dr. S. M. Condren Diatomic Molecules AOMOAO HH 2 H 1s ENERGY 1s B - AB B.O. = = = all electrons are paired, thus diamagnetic B => bonding electrons AB => antibonding electrons

31 Dr. S. M. Condren Diatomic Molecules AOMOAO HeHe 2 He 1s ENERGY 1s B - AB B.O. = = = Zero bond order means it does not exist

32 Dr. S. M. Condren Diatomic Molecules AOMOAO HeHe 2 He + 1s ENERGY 1s B - AB B.O. = = = 1/2 2 2 One unpaired electron, thus, paramagnetic +

33 Dr. S. M. Condren 1s nonbonding AO B AO B MO B 2 2s 2p

34 Dr. S. M. Condren Molecular Orbital Diagram side-by-side end-to-end bonding MO antibonding MO

35 Dr. S. M. Condren 1s nonbonding AO C AO C MO C 2 2s 2p

36 Dr. S. M. Condren 1s nonbonding AO O AO O MO O 2 2s 2p

37 Dr. S. M. Condren Energy


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