# CHMA10H3 Lecture Notes - Lecture 35: Lone Pair, Molecular Geometry, Chemical Polarity

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23 Nov 2018
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CHMA10 Lecture 32: Using VSPER to Predict Molecule Shape and Polarity
- Summarizing VSEPR Theory
o The geometry of a molecule is determined by the number of electron groups on
the central
Or on all interior atoms if there is more than one
o The number of electron groups can be determined from the Lewis structure of
the molecule
o There are numerous electron configurations that are classified as a single
electron group
A lone pair, a single bod, a double bond, a triple bond, and sometimes a
single electron all are classified as electron groups
o The geometry of electron groups is determined by their repulsions
Electron group repulsions vary as documented below: listed in order from
strongest to weakest repulsion
Lone Pair Lone Pair, Lone Pair- Bonding Pair, Bonding Pair
Bonding Pair
o Bond angles can vary from idealized angles because double and triple bonda
occupy more space than single bonds and lone pairs occupy more space than
bonding groups
The presence of lone pairs will usually reduce bond angles
Makes them smaller than the ideal angle for the particular
geometry
- Predicting molecule polarity
o 3 step process
1: Draw the Lewis structure for them molecule given and then determine
its molecular geometry
2: Determine if the bonds present in the given molecule are polar or non-
polar
Do this by calculating the electronegativity difference between
elements involved in the bonds
If there are absolutely no polar bonds present, then the molecule
is automatically deemed non-polar
3: Determine if adding polar bonds will give a net dipole movement
o Molecule shape and polarity
There are 2 main classifications we can use to look at molecules and
determine whether or not they are polar
1: Presence of polar bonds
o Check this by looking at the electronegativity difference
o The net dipole movement must be a non-zero value in
order for a bond to be deemed polar
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