5) Shapes and Intermolecular Forces

Question 1

Describe the repulsion between lone pairs and bonded pairs.

Answer 1

Lone pairs repel more than bonded pairs.

Question 2

For each lone pair in a molecule, how much is the bond angle reduced by?

Answer 2

2.5°.

Question 3

How many bonded pairs and lone pairs are there in a tetrahedral molecule? Give the bond angle.

Answer 3

• Bonded pairs: 4.
• Lone pairs: 0.
• Bond angle: 109.5°.

Question 4

How many bonded pairs and lone pairs are there in a pyramidal molecule? Give the bond angle.

Answer 4

• Bonded pairs: 3.
• Lone pairs: 1.
• Bond angle: 107°.

Question 5

How many bonded pairs and lone pairs are there in a non-linear molecule? Give the bond angle.

Answer 5

• Bonded pairs: 2.
• Lone pairs: 2.
• Bond angle: 104.5°.

Question 6

How many electron pair regions are there in a linear molecule? Give the bond angle.

Answer 6

• Electron regions: 2.

- Bond angle: 180°.

Question 7

How many electron pair regions are there in a trigonal planar molecule? Give the bond angle.

Answer 7

• Electron regions: 3.

- Bond angle: 120°.

Question 8

How many electron pair regions are there in an octahedral molecule? Give the bond angle.

Answer 8

• Electron regions: 6.

- Bond angle: 90°.

Question 9

Define electronegativity.

Answer 9

The ability of an atom to attract the bonding electrons in a covalent bond.

Question 10

What does electronegativity increase towards in the periodic table?

Answer 10

F.

Question 11

What is the bond type for something that has an electronegativity difference of 0?

Answer 11

Covalent.

Question 12

What is the bond type for something that has an electronegativity difference of 0-1.8?

Answer 12

Polar covalent.

Question 13

What is the bond type for something that has an electronegativity difference greater than 1.8?

Answer 13

Ionic.

Question 14

Predict the bond angle in an F2O molecule. Explain your answer.

Answer 14

• 104° – 105°.
• There are 2 bonded pairs and 2 lone pairs.
• Lone pairs repel more than bonded pairs.

Question 15

Describe and explain two anomalous properties of water which results from hydrogen bonding.

Answer 15

• Liquid H2O is denser than solid H2O. In a solid state, ice has an open lattice therefore, H2O molecules are held apart by hydrogen bonds.
• H2O has a relatively high boiling and melting point as the relatively strong hydrogen bonds need to be broken and a lot of energy is needed to overcome hydrogen bonds.

Question 16

Why does water have a high surface tension?

Answer 16

Strong hydrogen bonds on the surface.

Question 17

Explain, with the aid of a diagram, the intermolecular forces in H2O that lead to the relatively high boiling point of H2O. Use ‘Shapes & Imf’ card to test knowledge.

Answer 17

Rate knowledge 1-5.

Question 18

Suggest why H2S has a much lower boiling point than H2O.

Answer 18

No hydrogen bonding, therefore, weaker intermolecular forces.

Question 19

Explain why silicon has a much higher boiling point than phosphorus.

Answer 19

• Silicon has strong covalent bonds between atoms.

- Phosphorus has weak forces between molecules meaning that the London forces are easily broken.

Question 20

Explain why the boiling point increases from sodium to aluminium.

Answer 20

• From Sodium to Aluminium, the number of delocalised electrons increases.
• Therefore, the metallic bonding gets stronger.

Question 21

Name the shape of an NCl3 molecule.

Answer 21

Pyramidal.

Question 22

The O–H bonds in water and the N–H bonds in ammonia have dipoles. Why do these bonds have dipoles?

Answer 22

Oxygen/nitrogen is more electronegative which attracts a bonded electron pair more.

Question 23

Describe and explain the density of ice compared with water.

Answer 23

• Ice is less dense than water.

- Because hydrogen bonds hold H2O molecules apart in ice which causes an open lattice structure.

Question 24

Water and carbon dioxide both have polar bonds. Explain why water has polar molecules but carbon dioxide has non-polar molecules.

Answer 24

• CO2 is symmetrical, meaning the dipoles cancel.

- H2O is not symmetrical, meaning the dipoles don’t cancel.

Question 25

Explain Sodium Chloride’s solubility in water in terms of bonding and structure.

Answer 25

• Good solubility in water.

- Water is polar and the ions interact with water molecules.

Question 26

Explain graphite’s solubility in water in terms of bonding and structure.

Answer 26

• Insoluble.

- Graphite is non-polar, therefore no interaction with water.

Question 27

When given values for electronegativity, how are the bonds labelled?

Answer 27

• The atom with the larger electronegativity is given the 𝛿- symbol.
• The atom with the smaller electronegativity is given the 𝛿+ symbol.

Question 28

Describe how London forces arise.

Answer 28

-Uneven distribution of electrons.
-Creates an instantaneous dipole
-Which causes induced dipoles in neighbouring
molecules.