AS · Practice questions · Metallic bonding

Glue made of electrons.

Six original Cambridge-style questions on metallic bonding: the model, melting point trends, conductivity, malleability and a comparison with ionic lattices.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Ions in a sea of delocalised electrons.

Definition: attraction between positive ions and delocalised electrons.
Stronger with more electrons per atom, higher charge, smaller ions.
Conducts: delocalised electrons move.
Malleable: layers slide, bonding is non-directional.

Recall

[2 marks]

Describe the structure and bonding in a metal.

A giant lattice of positive metal ions surrounded by delocalised electrons. ✓
Metallic bonding is the electrostatic attraction between the positive ions and the delocalised electrons. ✓

Explain

[3 marks]

Explain why magnesium has a much higher melting point than sodium.

Magnesium forms Mg²⁺ ions and contributes two delocalised electrons per atom; sodium forms Na⁺ and contributes one. ✓
Mg²⁺ is also smaller than Na⁺. ✓
The attraction between the ions and the delocalised electrons is stronger in magnesium, so more energy is needed to melt it. ✓

Explain

[2 marks]

Explain why the melting point of potassium (63 °C) is lower than that of sodium (98 °C).

Both form 1+ ions and give one delocalised electron per atom. ✓
K⁺ is larger, so the attraction between the ions and the delocalised electrons is weaker. ✓

Explain

[2 marks]

Explain why aluminium is used for overhead power cables, referring to its bonding.

Aluminium has delocalised electrons that can move through the lattice, so it is a good electrical conductor. ✓
(It is also low density and can be drawn into wires because its layers of ions slide: it is ductile.) ✓

Explain

[3 marks]

Explain why a metal can be bent without breaking, whereas an ionic solid shatters.

In a metal the layers of positive ions slide over each other, and the delocalised electrons still surround them, so the metallic bonding is maintained. ✓
In an ionic solid a shift brings ions of the same charge together. ✓
They repel, and the crystal breaks. ✓

Analysis

[2 marks]

A student writes: “In a metal, the metal atoms share their electrons in covalent bonds.” Identify two errors in this statement.

The lattice is made of positive ions, not neutral atoms. ✓
The electrons are delocalised through the whole structure, not shared in localised covalent bonds between pairs of atoms. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.