1. Molecular Geometry and Bonding Theory
Chapter 9 AP Chemistry

2. Molecular Geometry
Molecular Geometry- general shape of a molecule as determined by the relative position of the nuclei.
The geometry and size of a molecule helps to determine it’s chemical behavior.
VSEPR- Valence-Shell-Electron-Pair-Repulsion model- predicts geometry based upon e’s around the central atom.

3. Principles of the VSEPR theory
Electrons are kept as far away from one another as possible – minimizing e pair repulsions
Electron pairs are considered as being bonding or non-bonding (lone pairs)
A multiple bond counts as a single bonding pair
Electron pair geometry is described by the regions of e’s around the central atom
Molecular geometry is a consequence of electron pair geometry.

4. Predicting Structures VSEPR
Derive the Lewis Structure to the form AXmEn
A = central atom
X = atoms bonded to the central atom
E = lone pairs of e’s on the central atom
M = # of bonded atoms
N = # of lone pairs

5. Electron Geometry Linear
Example
Electron and Molecular Geometry Linear
Bond angles 180
Sp Hybrid
Non-polar

6. More Examples AX2

7. Electron Geom. Trigonal Planar
Molecular Geom. Trigonal Planar
bond angles exactly 120 non-polar
Bent bond angles aprox 120 polar molecule
Sp2 hybridized

8. Electron Geom.Trigonal Planar
Molecular Geometry: AX3 (3BP or 2BP + 1LP) ex. 3bp NO3-
                                 <>

9. Examples Cont. 3bp
BF3 <>
                    <>

10. Examples Cont. 2bp + 1 lp
Ex O3 (ozone)

11. Electron Geom. Tetrahedral
Molecular Geom. Tetrahedral bond angles exactly non-polar molecule, Trigonal pyramidal bond angles aprox polar molecule, Bent bond angles aprox polar molecule
Sp3 hybridized

12. Molecular Geometry: AX4 [4BP or (3BP + 1LP) or (2BP + 2LP)]
Electron Geometry: AX4 Tetrahedral

13. Example
BrO3F, Perbromyl fluoride

14. Molecular Geometry: AX3E1 Trigonal Pyramidal

15. Example
NF3, Nitrogen trifluoride

16. Molecular Geometry: AX2E2 Bent/Angular

17. Example
H2O, Water,
ClOF, Chlorosyl fluoride

18. Electron Geom. Trigonal Bypyramidal
Mol. Geom. Trigonal Bypyramidal – bond angles ax. exactly 108 deg. eq. exactly 120 deg. Non-polar, See-Saw – bond angles ax. aprox. 108 deg. eq. aprox. 120 deg. Polar, T-shaped - bond angles ax. aprox. 108 deg. No –eq, Linear – bond angle exactly 180 non-polar.
All sp3d hybridized

19. Mol geo. Trigonal bipramidal
AX5 [5BP or (4BP + 1 LP) or (3BP + 2LP) or (2BP + 3LP)]
5bp

20. Example
PCl5(gas phase), Phosphorous pentachloride

21. Molecular Geometry: AX4E1 See-saw
Example IF2O2-

22. Molecular Geometry: AX3E2 T-structure
Example ClF3

23. Molecular Geometry: AX2E3 Linear
Examole XeF2

24. Electron Geometry Octahedrial
Mol geo. Octahedral – bond angle exactly non-polar, square pyramidal – bond angle aprox 90- polar, square planar- bond angle exactly 90 non-polar
Sp3d2 hybridized

25. Molecular Geometry: AX6 Octahedral
Example SF6

26. Molecular Geometry: AX4E1 Pyramidal Planar
Example XeOF4

27. Molecular Geometry: AX4E2 Square Planar
Example XeF4

28. Bond Angles
Non-bonding pairs of e’s take up more space (att. by one nucli) than bonded e pairs
Double and triple bonds take up more space than single bonds (more e’s)
Volume occupied lone pairs > triple bonds > double bonds > single bonds

29. Forces
Non-bonding pairs exert repulsive forces on adjacent e pairs and compress angles
Multiple bonds also exert repulsive forces and compress angles