Hybrid orbitals in chemistry as guide to learning chemistry

Chemistry

1. HYBRID ORBITALS A lecture prepared by: DR. LEONISA O. BERNARDO SLSU

2. Hybrid orbitals result from the mixing of atomic orbitals on the same atom. This mixing affects the spatial arrangement and energies of the hybrid orbitals . The hybrid orbital model (HOM), developed by Linus Pauling , attempts to explain the observed shapes and bond orders in molecules using hybrid orbitals on the individual atoms. When certain number of atomic orbitals are mixed, the same number of hybrid orbitals are obtained.

3. One way to think of what led Pauling to develop this model is to consider the methane molecule.

4. All carbon-hydrogen bonds in methane have the same length, and all H-C-H angles are equal, and equal to the tetrahedral angle of 109.47 o . Both of these facts are difficult to immediately rationalize given the spatial arrangement of the valence orbitals in C (the 2s and the three 2p orbitals), and the fact that the 2s orbital is filled in the ground state of the carbon atom.

5. A. sp 3 hybrid orbitals An s orbital mixed with all three p orbitals to create four equivalent sp 3 hybrids. ¼ s character + ¾ p character one s orbital + three p orbitals = four sp 3 hybrid orbitals

6. one s orbital + three p orbitals = four sp 3 hybrid orbitals

7. Example: Methane, CH 4 Now, make the model for methane and ethane, CH 3 CH 3 .

8. Molecular models using balloon 4 sp3 hybrid orbitals 1 2 3 4 109.5 sp 3 -sp 3 sp 3 sp 3 sp 3 sp 3 sp 3 sp 3 sp 3 -sp 3 sp 3 sp 3 sp 3 sp 3 sp 3 sp 3

9. B. sp 2 hybrid orbitals An s orbital mixed with two p orbitals creates three equivalent sp 2 hybrids. 1/3 s character + 2/3 p character one s orbital + two p orbitals = three sp 2 hybrid orbitals

10. one s orbital + two p orbitals = three sp 2 hybrid orbitals

11. Structure:

12. Molecular Models Using Balloons 1 unhybridized p orbital 3 sp 2 hybridized orbitals p-p orbitals overlap sp 2 -sp 2 orbitals overlap

13. C . sp hybrid orbitals An s orbital mixed with one 2p orbital to create two equivalent sp hybrids. ½ s character + ½ p character = sp hybrid one s orbital + one p orbitals = two sp hybrid orbitals

14. one s orbital + one p orbitals = two sp hybrid orbitals

15. Molecular Model Using Balloons 2 p unhybridized orbitals 2 sp hybridized orbitals p-p overlap p-p overlap sp-sp overlap

16. Covalent bonds are formed when an electron pair is shared between atoms. According to valence bond theory , electron sharing occurs by overlapping of two atomic orbitals . According to molecular orbital (MO) theory , bonds result from the mathematical combination of atomic orbitals to give molecular orbitals , which belong to the entire molecule. Bonding Concepts

17. Bonds that have a circular cross-section and are formed by head-on interaction are called sigma ( σ ) bonds . Bonds formed by sideways interaction of p orbitals are called pi ( π ) bonds . Example: Is it sigma or pi bond? Is the bond formed by the overlap of the 2 sp 3 orbitals a head-on interaction or sideways interaction?

18. 2 What orbitals are overlapping to form each of the following bonds? Classify whether the bond formed is sigma or pi? 1

19. 3 4 5

20. 6 8 7

21. Activity. ACTIVITY : A. (a) What orbitals are overlapping to form each of the following bonds? (b) Classify whether the bond formed is sigma or pi? (a) (b) 1 ___________ ___________ 2 ___________ ___________ 3 ___________ ___________ 4 ___________ ___________ 5 ___________ ___________ 6 ___________ ___________ 7 ___________ ___________

22. (a) (b) 8 __________ __________ 9 __________ __________ 10 __________ __________ 11 __________ __________ 12 __________ __________ 13 __________ __________ 14 __________ __________ 15 __________ __________ 16 __________ __________ 17 __________ __________

23. B. What is the angle between bonds in each of the following? Angle 18 __________ 19 __________ 20 __________ 21 __________ 22 __________ 23 __________ 24 __________ 25 __________ 26 __________