Simple molecular structures
4 marks · NormalA student compares the properties of diamond (a giant covalent structure) with carbon dioxide (a simple molecular compound).
State one difference between the melting points of diamond and carbon dioxide.
Explain this difference in terms of bonding and structure.
Which of the two substances can conduct electricity? Explain your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Diamond has a much higher melting point than carbon dioxide. · must show diamond very high melting point; CO2 low melting point
(b) Diamond's atoms are held together by strong covalent bonds in a giant structure, requiring much energy to break. CO2 molecules have weak intermolecular forces and are easy to separate. · must show diamond: strong covalent bonds; giant network, CO2: weak intermolecular forces; simple molecules
(c) Neither diamond nor carbon dioxide conducts electricity because both lack free electrons or ions. · must show neither conducts electricity; no free electrons or ions
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States melting point of diamond is much higher than CO2.
B2 (b) · 1 mark · Diamond has strong covalent bonds in a giant network requiring much energy to break.
B3 (b) · 1 mark · CO2 has weak intermolecular forces between simple molecules.
B4 (c) · 1 mark · Correctly states that neither substance conducts electricity and explains.
Worked solution
a) Diamond has a much higher melting point than carbon dioxide.
b) Diamond consists of many carbon atoms joined in a giant network by strong covalent bonds, which require much energy to break. CO2 is a simple molecule with weak intermolecular forces, so less energy is needed for melting/boiling.
c) Neither diamond nor carbon dioxide conducts electricity because neither contains free electrons or ions.