2. 3.2 VSEPR Theory

3. VSEPR Theory Valence Shell Electron Pair Repulsion
Predicts the 3-D geometry of molecules (covalent compounds)
The structure around a given atom is determined by minimizing electron-pair repulsions (getting pairs of electrons as far apart as possible)
Bonding geometry always starts out with 4 bonding areas in a tetrahedral shape.
Molecule geometry depends on bonding pairs.
This can either bonding or lone pair
109.5o

4. Shapes Tetrahedral and trigonal planar are non-polar.
Pyramidal and bend are polar.

5. Shapes Tetrahedral – 4 bonding e- groups
Pyramidal – 3 bonding e- groups, 1 lone pair
Bent – 2 bonding e- groups, 2 lone pairs
Trigonal Planar – 3 bonding e- groups
Linear – 1 or 2 bonding e- groups
Tetrahedral and trigonal planar are non-polar.
Pyramidal and bend are polar.

6. Compounds with only 2 or 3 valence e- Can break the octet rule
BF3
BeH2 •• •• • F B F • •• •• H Be H • F • ••
Linear
Trigonal Planar
Exceptions:
Hydrogen = 2 valence e-
Beryllium = 4 valence e-
Boron = 6 valence e-

7. Most compounds with double or triple bonds are linear
C2H4 C C H H
C2H2 H C C H
Bond Length
Bond length increases with atom size
Multiple bonds (double and triple) are shorter than single bonds

8. Bond Angles
Bond angles are determined by the number of non-bonding pairs of electrons which push the bonding pairs closer together
Shape
Angle of Bond
Linear
180°
Bent
<109.5°
Trigonal planar
120°
Trigonal pyramidal
Tetrahedral
109°

9. Intermolecular Forces
From strongest to weakest:
Covalent Bond
Ionic Bond
Metallic Bond
Hydrogen Bonding
Dipole-Dipole Forces
Dispersion Forces
Intramolecular Forces
metallic bonding

10. Intermolecular Forces
Metallic Bond – positive nuclei in a SEA of electrons

11. Dispersion Forces Found between nonpolar covalent molecules
They occur when the electrons around a molecule become unevenly distributed, causing a slight dipole (positive end & negative end)

12. Dipole-Dipole Polar covalent molecules have permanent dipoles.
The attractions between the partial charges on the ends of the polar molecules are called dipole-dipole forces.
Partial charge symbol (Lowercase sigma)

13. (add these to your VSEPR shapes notes)
Polarity
(add these to your VSEPR shapes notes)
Tetrahedral – nonpolar
Pyramidal – polar
Bent – polar
Trigonal Planar – nonpolar
Linear – nonpolar
Tetrahedral and trigonal planar are non-polar.
Pyramidal and bend are polar.

14. Hydrogen Bonding Special type of dipole-dipole forces.
It only occurs between molecules with H bonded to N, O, or F.
Hydrogen bonding is stronger than normal dipole-dipole forces.