1. Valence Shell Electron Pair Repulsion Theory
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 structure total shared unshared H
CH H-C-H “tetrahedral”
NH H-N-H “trigonal
H pyramidal”
H2O H-O-H “bent”

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

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

7. Typically. . . Symmetric (non-polar) Asymmetric (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 “Like dissolves like”
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. Paraffin
Water