Summary UQ CHEM1100 Module 2: Detailed notes and examples

UQ CHEM1100: Module 2
Bonding & Geometry

Table of Contents
Section 1: VSEPR and Electron Domains .................................................................... 2
1. Electron Geometry (The "Skeleton").................................................................... 2
2. Molecular Geometry (The "Visible Shape") .......................................................... 2
3. Practice Molecules............................................................................................ 2
Section 2: Hybridization (sp, sp^2, sp^3) ................................................................... 6
The Explanation .................................................................................................... 6
Example 1: CO2 (Carbon Dioxide) .......................................................................... 7
Example 2: BF3 (Boron Trifluoride) ......................................................................... 7
Example 3: PCl5 (Phosphorus Pentachloride) ......................................................... 7
Example 4: SO2 (Sulfur Dioxide)............................................................................. 7
Example 5: BrF5 (Bromine Pentafluoride) ............................................................... 7
Section 3: Intermolecular Forces (IMFs) ..................................................................... 8
The Explanation .................................................................................................... 8
Example Problem ................................................................................................. 8

, Section 1: VSEPR and Electron Domains
The Explanation: Valence Shell Electron Pair Repulsion (VSEPR) theory states that
electron pairs (bonds or lone pairs) stay as far apart as possible to minimize repulsion.

1. Electron Geometry (The "Skeleton")
This is the arrangement of all electron domains around the central atom. A "domain" is
any area of high electron density. This includes:

• A single, double, or triple bond (each counts as one domain).

• A lone pair of electrons (counts as one domain).

If there are 4 domains, the Electron Geometry is always Tetrahedral, regardless of
whether those domains are bonds or lone pairs.

2. Molecular Geometry (The "Visible Shape")
This is the arrangement of only the atoms (the bonds). We "ignore" the lone pairs when
naming the shape, but we cannot ignore their effect.

• The "Fat" Lone Pair Rule: Lone pairs take up more space than bonding pairs.
They "squeeze" the bonds together, making the bond angles slightly smaller than
the ideal "skeleton" angles.

3. Practice Molecules
1. CH4 (methane)

2. NH3 (ammonia)

3. H2O (water)

4. SF4 (sulphur tetrafluoride)

5. XeF4 (Xenon Tetrafluoride)



For each molecule, follow these steps:

• Count Valence Electrons.

• Draw the Lewis Structure.

• Count total domains (Bonds + Lone Pairs) -> Electron Geometry.

• Identify shape based on atoms only -> Molecular Geometry.

• Estimate the angles.