Valence Shell Electron Pair Repulsion Theory VSEPR Valence Shell Electron Pair Repulsion Theory

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

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

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

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

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

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

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

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”

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

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

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

Paraffin Water