VSEPR model diagrams showing molecular geometries based on electron pair repulsion.

Problem Description:

The worksheet explains the VSEPR (Valence Shell Electron Pair Repulsion) model, which predicts the molecular shapes based on the repulsion between electron pairs around a central atom. The goal is to understand how the number of electron groups (both bonding and lone pairs) around a central atom determines the molecular geometry.

Key Points from the Worksheet:

1. Six Groups: Form an octahedron.
- All angles are \(90^\circ\) or \(180^\circ\).
- All positions are equivalent.

2. Five Groups: Form a trigonal bipyramid.
- Two axial positions at \(180^\circ\) to each other.
- Three equatorial positions at \(120^\circ\) to each other.
- Lone pairs occupy equatorial positions due to more space.

3. Four Groups: Form a tetrahedron.
- All angles are \(109.5^\circ\).
- All positions are equivalent.

4. Three Groups: Form a flat triangle (trigonal planar).
- All angles are \(120^\circ\).
- All positions are equivalent.

5. Two Groups: Form a linear shape.
- Angle between them is \(180^\circ\).

Application to Chemistry:

- Electron groups can be either bonding pairs (atoms bonded to the central atom) or lone pairs (non-bonding electrons on the central atom).
- Lone pairs occupy more space than bonding pairs, so they tend to occupy positions that maximize distance from other electron groups.

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Solution Explanation:

To solve problems involving molecular shapes using the VSEPR model, follow these steps:

#### Step 1: Draw the Lewis Structure
- Determine the central atom.
- Count the total number of valence electrons.
- Distribute electrons to satisfy the octet rule for all atoms.
- Identify bonding pairs and lone pairs around the central atom.

#### Step 2: Count the Electron Groups
- Each single bond, double bond, or triple bond counts as one electron group.
- Each lone pair on the central atom also counts as one electron group.
- Total electron groups = Bonding pairs + Lone pairs.

#### Step 3: Predict the Geometry
- Use the VSEPR model to determine the geometry based on the total number of electron groups:
- 2 groups: Linear
- 3 groups: Trigonal planar
- 4 groups: Tetrahedral
- 5 groups: Trigonal bipyramidal
- 6 groups: Octahedral

#### Step 4: Account for Lone Pairs
- Lone pairs occupy positions that minimize repulsion.
- In trigonal bipyramidal geometry, lone pairs prefer equatorial positions.
- In general, lone pairs will occupy positions that maximize their distance from other electron groups.

#### Step 5: Determine the Molecular Shape
- The molecular shape is determined by the positions of the atoms only (ignoring lone pairs).
- If there are no lone pairs, the molecular shape matches the electron-group geometry.
- If there are lone pairs, the molecular shape will be distorted from the electron-group geometry.

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Example Problem:

Predict the molecular shape of SF₆ (Sulfur Hexafluoride).

#### Step 1: Draw the Lewis Structure
- Central atom: Sulfur (S)
- Valence electrons: \(6\) (S) + \(7 \times 6\) (F) = \(48\)
- Sulfur forms six single bonds with fluorine atoms.
- No lone pairs on sulfur.

#### Step 2: Count the Electron Groups
- Six single bonds = Six electron groups.

#### Step 3: Predict the Geometry
- Six electron groups → Octahedral geometry.

#### Step 4: Account for Lone Pairs
- No lone pairs present.

#### Step 5: Determine the Molecular Shape
- Since there are no lone pairs, the molecular shape is the same as the electron-group geometry.
- Molecular Shape: Octahedral.

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Final Answer:

For SF₆, the molecular shape is:
\[
\boxed{\text{Octahedral}}
\]

This approach can be applied to any molecule to predict its shape using the VSEPR model.