AQA GCSE Chemistry (8462), Higher tier · Bonding, structure and the properties of matter › Bonding, structure and properties
Practise Properties of small molecules. 14 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Explain why substances that consist of small molecules do not conduct electricity.
The molecules do not have an overall electric charge.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Many covalent substances consist of small molecules.
(a) Complete the sentence. Tick (✓) one box. Substances that consist of small molecules are usually ................[1]
gases or liquids
hard solids
metals
good conductors of electricity
(b) What is overcome when water boils? Tick (✓) one box.[1]
Covalent bonds
Intermolecular forces
Ionic bonds
Metallic bonds
(c) Explain why substances that consist of small molecules do not conduct electricity.[1]
(d) Methane boils at −162 °C. What is the state of methane at room temperature?[1]
Show the answer and mark scheme
(a)Answer: gases or liquids
(b)Answer: Intermolecular forces
(c)Answer: The molecules do not have an overall electric charge.
the molecules have no overall (electric) charge
(d)Answer: gas
gas
Question 2Medium5 marks
To boil one mole of water needs 41 kJ of energy. To break all of the O–H covalent bonds in one mole of water molecules needs 928 kJ of energy.
(a) Calculate how many times more energy is needed to break the covalent bonds in one mole of water than to boil one mole of water.[2]
(b) A student said: 'When water boils, the covalent bonds break and the molecules split up into hydrogen and oxygen.' Use the data to explain why the student must be wrong.[1]
(c) Describe what happens to the water molecules when water boils.[2]
Show the answer and mark scheme
(a)Answer: 23 (22.6)
928 ÷ 41
22.6 / 23
(b)Answer: If the covalent bonds broke, about 928 kJ would be needed to boil one mole of water, but only 41 kJ is needed.
breaking the covalent bonds would need 928 kJ per mole, but boiling needs only 41 kJ per mole / boiling needs far less energy than breaking the bonds
(c)Answer: The weak intermolecular forces between the water molecules are overcome, and the molecules move far apart and move randomly as a gas (steam).
the (weak) intermolecular forces / forces between the molecules are overcome
the molecules move far apart / move randomly and quickly as a gas
Question 3Hard8 marks
Sulfur exists as S8 molecules. Sulfur melts at 115 °C. Oxygen exists as O2 molecules. Oxygen melts at −218 °C. Relative atomic masses (Ar): O = 16, S = 32
(a) Calculate the relative formula mass of S8.[1]
(b) Explain why sulfur has a much higher melting point than oxygen.[3]
(c) Explain why molten sulfur does not conduct electricity.[2]
(d) White phosphorus exists as P4 molecules (Mr = 124). Predict whether white phosphorus has a higher or a lower melting point than sulfur. Give a reason for your answer.[2]
Show the answer and mark scheme
(a)Answer: 256
256
(b)Answer: S8 molecules are much larger (Mr 256 compared with 32), so the intermolecular forces are stronger and more energy is needed to overcome them.
S8 molecules are (much) larger / have a higher relative formula mass (than O2)
so the intermolecular forces are stronger
so more energy is needed to overcome the intermolecular forces
(c)Answer: Sulfur is made of molecules with no overall charge; there are no ions or delocalised electrons to carry charge.
sulfur is made of molecules with no overall charge
(so) there are no ions / delocalised electrons free to move (and carry charge)
(d)Answer: Lower, because P4 molecules are smaller than S8 molecules, so the intermolecular forces are weaker.
lower
P4 molecules are smaller / have a lower Mr than S8, so weaker intermolecular forces