Simple molecular structures
2 marks · HardExplain, using ideas about bonds and forces, why melting a substance with a simple molecular structure requires much less energy than melting a giant covalent structure such as diamond.
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.
Show answer
Also accept: In a simple molecular structure, only weak intermolecular forces are broken when melting, which require little energy, whereas in a giant covalent structure, strong covalent bonds must be broken, which require much more energy.; Melting a simple molecular substance breaks weak intermolecular forces, but melting a giant covalent structure breaks strong covalent bonds, needing much more energy.
Common mistakes: Saying covalent bonds are broken in both structures when melting (not true for simple molecular).; Not mentioning intermolecular forces.
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Identifies that only intermolecular forces are broken in simple molecular structures when melting (not covalent bonds).
M2 · 1 mark · States that giant covalent structures require breaking strong covalent bonds (which need much more energy).
Worked solution
In a simple molecular structure, melting requires only breaking the weak intermolecular forces between molecules, which needs little energy. In a giant covalent structure like diamond, strong covalent bonds must be broken to melt it, which requires much more energy.