Metallic Bonding
4 marks · NormalThe table below shows data for three metals.
| Metal | Ion formed | Number of delocalised electrons per atom | Melting point (°C) |
|---|---|---|---|
| Sodium | Na+ | 1 | 98 |
| Magnesium | Mg2+ | 2 | 650 |
| Aluminium | Al3+ | 3 | 660 |
Use the data to answer the questions.
For sodium, write the charge on the ion and state how many delocalised electrons each atom provides.
Explain, using the table, why magnesium has a much higher melting point than sodium.
Suggest, using the data, why aluminium and magnesium have similar melting points despite aluminium having a higher ion charge.
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
(a) Na+, charge +1, 1 delocalised electron per atom.
(b) Magnesium forms Mg2+ ions and provides 2 delocalised electrons per atom. This causes stronger electrostatic attractions and stronger metallic bonding, so a higher melting point than sodium.
(c) Melting point of aluminium is similar to magnesium possibly due to differences in lattice structure or atomic size affecting the overall forces.
Also accept: Aluminium may have more closely packed lattice or other structure-related effects
Common mistakes: Ignoring the number of delocalised electrons; Assuming more charge always means much higher melting point
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States sodium ion is Na+, charge +1, with 1 delocalised electron per atom.
M1 (b) · 1 mark · Identifies that magnesium's ion has a greater charge (2+) and provides 2 delocalised electrons.
A1 (b) · 1 mark · Explains these factors cause stronger electrostatic attractions and higher melting point.
B2 (c) · 1 mark · Suggests the similar melting point for Al and Mg may be due to lattice structure, atomic size or other factors affecting the strength of bonding.
Worked solution
a) Sodium forms Na+ ions (charge +1). Each sodium atom provides 1 delocalised electron.
b) Magnesium forms Mg2+ ions and provides 2 delocalised electrons per atom. The higher charge and greater number of delocalised electrons mean stronger electrostatic attractions and stronger metallic bonding, which increases the melting point compared to sodium.
c) The similar melting points for aluminium and magnesium, despite aluminium's higher ion charge, may be explained by factors like atomic size or packing in the lattice affecting the bond strength.