V alence S hell E lectron P air R epulsion Theory

1. Planar triangular ValenceShellElectronPairRepulsionTheory Tetrahedral Trigonal pyramidal Bent

2. Molecular Shape VSEPR theory assumes that the shape of a molecule is determined by the repulsion of electron pairs.

3. VSEPR Theory • Based on Lewis structures • Theory predictsshapesof compounds • VSEPR (pronounced “vesper”) stands for Valence Shell Electron Pair Repulsion • VSEPR predicts shapes based on electron pairs repelling (in bonds or by themselves) • Electronsaround central nucleus repeleach other. So, structures have atoms maximally spread out

4. VSEPR overview • Each shape has a name • Names of Shapes: • tetrahedral • trigonal pyramidal • Bent • Linear • trigonal planar

5. Models Tetrahedral TriangularPlanar Bent or V Linear Trigonal pyramidal

6. 109.5° methane, CH4 Tetrahedral Bonds are all evenly spaced electrons

7. .. .. .. .. ammonia NH3 Trigonal Pyramidal Less repulsion between the bonding pairs of electrons

8. .. .. 109.5° (109.5°) 109.5° (107°) 109.5° (104.5°) .. water, H2O

9. Bent or V 2 unshared pairs of e’s at top of O repel bonds and force them to bend

10. Tetrahedral 4 Trigonal Pyramidal 4 (3 shared 1 lone pair)

11. Bent 4 (2 shared 2 lone pairs) Linear CO2 2

12. Linear 2 Trigonal Planar 3

13. Hybrid Orbitals • VSEPR works well for shapes/geometry, but not for describing the types of bonds formed • Hybridization: the mixture of atomic orbitals to form the same number of new orbitals • Carbon is the most common element that undergoes hybridization

14. Methane Hybrid Orbitals • Electron configuration of methane: [He]2s22p2 • One s and three p orbitals hybridize to form four sp3 orbitals

15. Molecular Shape/Hybrid Orbitals: Linear/sp Trigonal planar/sp2 Tetrahedral/sp3 Trigonal pyramidal/sp3 Bent/sp3

16. Phosphorus trihydride • Total number of valence electrons: 8 • Lewis structure: three single bonds and one lone pair • Shape: trigonal pyramidal • Four bonding positions = sp3 hybrid

17. Intermolecular Forces • Forces that hold together identical particles such as water molecules in a drop of water • Three such forces are: dispersion forces, dipole-dipole forces, and hydrogen bonds

18. Dispersion Forces • Also known as London forces • Weak forces that result from a temporary shift in the density of electrons in electron clouds • For example, if two nonpolar molecules collide, the electron clouds of one molecule repels the electron cloud of the other molecule, creating a greater electron density in on region of each electron cloud

19. Dipole-Dipole Forces • Attractions between oppositely charged regions of polar molecules • Since dipoles in polar molecules are permanent, dipole-dipole forces are stronger than dispersion as long as the molecules are similar in mass.

20. Hydrogen Bonds • Type of dipole-dipole attraction • Occurs between molecules containing a hydrogen atom bonded to a small, highly electronegative atom with at least one lone pair (i.e., fluorine, oxygen, or nitrogen) • F, O, and N are electronegative enough to cause a large partial positive charge on the H, but small enough to allow their lone pairs to come close to H atoms