Chemical Bonding (Ionic, Covalent and Metallic): Question 10
Syllabus 2.7
An electrician upgrades the wiring in an old building, replacing aluminium cables with copper cables, because copper is an even better electrical conductor. Which statement correctly explains, in terms of structure and bonding, why a metal such as copper conducts electricity?
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Worked solution
Step 1: Recall the metallic bonding model
A metal such as copper consists of a giant lattice of positive metal ions surrounded by a “sea” of delocalised electrons. Electrons that are not fixed to any one atom or ion and are free to move throughout the whole structure. A strong electrostatic attraction between the positive ions and the delocalised electrons holds the metallic lattice together.
Step 2: Apply this to electrical conduction
When a voltage is applied across a piece of copper, the delocalised electrons are able to drift through the lattice, moving from one end to the other. This flow of charged electrons through the structure is what constitutes an electric current. The positive copper ions themselves remain in their fixed lattice positions throughout. It is the electrons that move, not the ions. Because the delocalised electrons are already free to move within the solid lattice, copper conducts electricity well even without being melted.
Why the other options are wrong
- B: copper is held together by metallic bonding, not covalent bonding. There are no fixed shared pairs of electrons between specific pairs of copper atoms, and current is carried by electrons moving through the structure, not vibrating in place.
- C: in a solid metal, it is the delocalised electrons that move to carry the current, not the metal ions, which remain in fixed lattice positions (unlike in a molten ionic compound, where the ions themselves are free to move).
- D: copper atoms lose only their outer-shell (delocalised) electrons, not every electron; the resulting positive ions still have their inner electron shells intact and are not “bare nuclei”.
Final answer
The correct statement is : copper’s outer-shell electrons become delocalised, forming a “sea” of electrons that moves freely through the lattice and carries charge, while the positive copper ions remain in fixed positions.