Question 1
Paper 2Hard8 marksA materials team is screening pure chromium, iron and copper for a component. The specification requires a melting point above 1400 °C; among metals that meet this limit, the electrical conductivity at 20 °C should be as high as possible. Approximate values are shown.
| Metal | Melting point / °C | Electrical conductivity at 20 °C / S m⁻¹ |
|---|---|---|
| Chromium | 1907 | 7.9 × 10⁶ |
| Iron | 1538 | 1.00 × 10⁷ |
| Copper | 1085 | 5.96 × 10⁷ |
(a)[2]
Describe the metallic model for a transition element, including the role of d-electrons.
(b)[2]
Explain how this model accounts for electrical conductivity.
(c)[4]
A trainee claims: “The metal with the greatest electrical conductivity must have the strongest metallic bonding and the highest melting point.” Assess this claim using the data and the metallic model, and identify the metal that meets the specification.