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Lecture 31 11/18/05
Electron Pair Geometries
Molecules with only single covalent bonds around central atom.
Axial atoms Equatorial atoms
Repulsion
Lone pair – Lone pair
Lone pair – Bonding pair
Bonding pair – Bonding pair
Highest repulsion
Geometries for Four Electron Pairs
Molecular Geometries for Five Electron Pairs
Molecular Geometries for Six Electron Pairs
Example: What is the geometry of NH3?
1. Draw Lewis structure2. Determine # of bonds and lone pairs around central atom3. Electron-pair geometry4. Molecular geometry
Formaldehyde, CH2O
••
C HH
O••
••
CHH
O••
1. Draw Lewis structure
2. Determine # of bonds and lone pairs around central atom
3. Electron-pair geometry
4. Molecular geometry
Molecular polarity dependent on two things: Bond polarity Geometry
Dipole Moment Measurement of the molecular polarity
Molecular Polarity
CO2 and H2O
Which one is polar?
Intermolecular Forces (IMF)Noncovalent interactions
Influence propertiesMelting pointBoiling point
Greater the IMF, higher the boiling pointSolubility
Like dissolves likeStructure of complex molecules like
proteins
Beta-carotene
Dipole-Dipole attractionPolar / Polar interaction
More polar molecules greater IMF
5 – 25 kJ/mol (150-1000 KJ/mol – covalent bond)
Polar molecules can induce a dipole in non-polar molecules Polarization
Polarizability Degree to which electron cloud can be distorted to form dipole Higher the molar mass, greater the polarizibility
Dipole / Induced Dipole ForcesPolar / non-polar interaction