VSEPR

1. VSEPR Valence Shell Electron Pair Repulsion Theory

2. VSEPR • e- pairs repel each other so they are oriented as far apart as possible.

3. VSEPR Rules • Draw the Lewis Structure for the molecule • Count the total number of . . . • Bonded regions around the central atom • DOUBLE and TRIPLE bonds count as ONE REGION • Unshared e- pair • Count as ONE REGION

4. Molecular Lewis Dot electron pairs around central atom Structure structuretotalsharedunshared H CH4 H-C-H 4 4 0 “tetrahedral” H NH3 H-N-H 4 3 1 “trigonal H pyramidal” H2O H-O-H 4 2 2 “bent”

5. Total no. of electron pairs No. of shared pairs No. of unshared pairs Molecular shape Molecule

6. Polarity • A molecule is polar if • There is a polar bond • It is ASSYMETRICAL (not symmetric) (+) H (-) O (+) H H C H H (+) (+) (+) H Polar (+) Non-Polar

7. Typically. . . • Symmetric (non-polar) • Linear • Tetrahedral • Trigonal planar • If all elements around the center atom are the same • Asymmetric (polar) • Bent • Trigonal pyramidal

8. If a central atom is symmetrically surrounded by identical atoms it will be non-polar • Linear AB2 • Trigonal planar AB3 • Tetrahedral AB4

9. Liquids • Miscible – 2 liquids that dissolve in each other • Immiscible – 2 liquids that do not dissovle in each other, they separate • “Like dissolves like”

10. Intermolecular Forces • Van der Waals forces (London Dispersion forces) • Weak forces between non-polar molecules • These forces determine volatility • Doesn’t take much nrg to break apart (liquid gas) • Most likely to be a gas • Like playing red rover and only holding pinkies together

11. Intermolecular Forces • Dipole-Dipole • Attraction between polar molecules • Most likely to be a liquid • Play red rover and hold hands

12. Intermolecular Forces • Hydrogen Bonding (H-Bonds) • Between hydrogen (H) and a highly electronegative element • F, O, N • Extreme case of dipole-dipole • Strongest of the intermolecular forces • Play red rover and link elbows • Needs A LOT of nrg to break bonds

13. Water Paraffin