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OCR A-level Chemistry Molecular shapes

Molecular shapes

This page covers the following topics:

1. VSEPR
2. Molecular shapes
3. Common examples of molecular shapes

Valence shell electron-pair repulsion (VSEPR) theory are a set of rules which explain the geometry that molecules adopt. The rules are governed by finding the lowest energy conformation, holding both the bonding electrons and lone-pair electrons as far apart as possible.

VSEPR

The geometric shapes that molecules adopt have names and specific bond angles, which optimise electron repulsion to maintain the lowest energy configuration. The presence of lone-pairs of electrons can distort the geometry, due to their stronger electron repulsion.

Molecular shapes

There are some molecules whose geometries are assumed to be common knowledge. However, for unseen molecules it expected that their geometry can be determined using the VSEPR rules.

Common examples of molecular shapes

1

What geometry does COβ‚‚ adopt?

What geometry does COβ‚‚ adopt?

2

Draw a molecule of ClF₃, stating its geometry.

Draw a molecule of ClF₃, stating its geometry.

3

How many bonding pairs of electrons and lone pairs of electrons does SFβ‚„ have? What geometry does it adopt?

How many bonding pairs of electrons and lone pairs of electrons does SFβ‚„ have? What geometry does it adopt?

4

Sketch a molecule of methane, indicating the bond angles.

Sketch a molecule of methane, indicating the bond angles.

5

Which type of electrons exerts the largest repulsion, bonding electrons or lone-pair electrons?

Which type of electrons exerts the largest repulsion, bonding electrons or lone-pair electrons?

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