Question

State the properties of copper and aluminium which make them good conductors of electricity.

Answer 1

1. Presence of Delocalized Valence Electrons

This is the most fundamental reason.
What it is: In metallic bonding, the outermost electrons (valence electrons) of the atoms are not tied to any single atom. Instead, they detach and form a mobile "sea of electrons" that flows freely throughout the metal's entire crystal lattice structure.
For Copper (Cu): Each copper atom contributes one valence electron to this sea.
For Aluminium (Al): Each aluminium atom contributes three valence electrons.
Why it matters: When a voltage is applied across the metal, these delocalized electrons are free to move in a directed way, creating an electric current. The more easily these electrons can move, the better the conductor.

2. Low Electrical Resistivity

This is the measurable outcome of the free-flowing electrons.
What it is: Resistivity is an intrinsic property of a material that measures how strongly it opposes the flow of electric current. Good conductors have very low resistivity.
For Copper: It has a resistivity of approximately 1.68 x 10⁻⁸ Ω·m at 20°C. This is the second-lowest of any pure metal (only silver is better).
For Aluminium: It has a resistivity of approximately 2.65 x 10⁻⁸ Ω·m at 20°C. While higher than copper's, this is still extremely low compared to other materials.
Why it matters: Low resistivity means that very little energy is lost as heat when current passes through the material, making the transmission of electricity highly efficient.

3. Favourable Crystalline Structure

• What it is: The atoms in both copper and aluminium are arranged in a regular, repeating crystal lattice (a Face-Centered Cubic structure). This orderly arrangement provides relatively clear pathways for the sea of electrons to move through.
• Why it matters: A uniform structure minimizes the number of collisions electrons have with the lattice, which would otherwise impede their flow and increase resistance. While all metals have some resistance due to atomic vibrations (which increase with temperature) and impurities, the structure of copper and aluminium is highly conducive to electron flow.

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Comparison Summary: Copper vs. Aluminium

| Property | Copper (Cu) | Aluminium (Al) | Significance |
| :--- | :--- | :--- | :--- |
| Conductivity | Higher. It is the international standard against which other conductors are measured (100% IACS). | Lower. About 61% of copper's conductivity by volume. | For a given cross-sectional area, copper can carry more current. |
| Density | High (8.96 g/cm³) | Low (2.70 g/cm³) | Aluminium is much lighter, making it ideal for overhead power lines where weight is a critical factor. |
| Cost | More Expensive | Less Expensive | Aluminium is a more economical choice, especially for large-scale projects. |
| Corrosion | Oxidizes (patinates), but the layer is conductive. | Rapidly forms a very tough, thin, non-conductive oxide layer. | The oxide layer on aluminium must be removed at connection points to ensure a good electrical contact. |

In summary, the core reason both metals are excellent conductors is their abundant sea of mobile electrons combined with a crystal structure that allows these electrons to move with very low resistance. While copper is the better conductor, aluminium's low density and lower cost make it a vital material for specific applications like long-distance power transmission.