The shapes of molecules and ions

How does electrons in molecules exist?

In pairs in volumes of space called orbitals

What do pairs of electrons do?

Repel each other

What do electron pairs do to minimise repulsion?

Take up positions as far apart as possible from each other

What does the shape of a simple molecule depend on?

The number of pairs of electrons that surround the central atom

How do you work out the shape of any molecule?

Draw a dot-and-cross diagram to find the number of pairs of electrons

What is the bond angle of a linear molecule?

180°

What is the bond angle of a trigonal planar molecule?

120°

What is the bond angle of a tetrahedral molecule?

109.5°

Do the charges of ions affect the shape?

No

What are the bond angles of a trigonal bipyramid molecule?

90° and 120°

What is the bond angle of an octahedral molecule?

90°

Are lone pairs apart of the covalent bond?

No

How do lone pairs affect bond angles?

For each lone pair, the bond angle of 109.5° reduces by 2.5°

Chlorine tetrafluoride ion

Example of a square planar molecule

Repulsion between electron pairs

What is the shape of the molecule if there are:

• 2 electron pairs

• 2 bond pairs

• 0 lone pairs

Linear

Bond angle between linear molecule

180°

What is the shape of the molecule if there are:

• 3 electron pairs

• 3 bond pairs

• 0 lone pairs

Trigonal planar

Bond angle between trigonal planar molecule

120°

What is the shape of the molecule if there are:

• 4 electron pairs

• 4 bond pairs

• 0 lone pairs

Tetrahedral

Bond angle between tetrahedral molecule

109.5°

What is the shape of the molecule if there are:

• 5 electron pairs

• 5 bond pairs

• 0 lone pairs

Trigonal bipydramid

Bond angle between trigonal planar molecule

90° and 120°

What is the shape of the molecule if there are:

• 6 electron pairs

• 6 bond pairs

• 0 lone pairs

Octahedral

Bond angle between octahedral molecule

90°

What is the shape of a molecule if there are:

• 4 electron pairs

• 3 bond pairs

• 1 lone pair

Triangular pyramidal

Bond angle between a triangular pyramidal molecule

109.5 - 2.5 (1 lone pair) = 107°

Molecular shape of ammonia (NH₃)

Triangular pyramidal

What is the shape of a molecule if there are:

• 4 electron pairs

• 2 bond pairs

• 2 lone pairs

Angular

Bond angle between an angular molecule

109.5 - (2 × 2.5) (2 lone pairs) = 104.5°

Molecular shape of water (H₂O)

Angular

What is the shape of a molecule of there are:

• 6 electron pairs

• 4 bond pairs

• 2 lone pairs

Square planar

Bond angle between a square planar molecule

90

Molecular shape of chlorine tetrafluoride ion (ClF₄⁺)

Square planar