IB Chemistry HL S2.3 The metallic model questions

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Question 1

Paper 2Hard8 marks

A 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.

MetalMelting point / °CElectrical conductivity at 20 °C / S m⁻¹
Chromium19077.9 × 10⁶
Iron15381.00 × 10⁷
Copper10855.96 × 10⁷
(a)

Describe the metallic model for a transition element, including the role of d-electrons.

[2]
(b)

Explain how this model accounts for electrical conductivity.

[2]
(c)

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.

[4]

Question 2

Paper 2Hard8 marks

A chemistry student uses the metallic model to explain properties of lithium and to assess claims about Group 1 metals. Figure 1 shows a simplified model of lithium before and during shear. The table gives first ionization energies.

ElementFirst ionization energy / kJ mol⁻¹
Li520
Na496
K419
(i) Before shear(ii) During shearLi+Li+e−e−FFSchematic diagram, not to scale

A student argues: “The decrease in first ionization energy from Li to K explains the increase in Group 1 reactivity. It also proves that metallic bonding becomes stronger, so potassium must conduct electricity better than lithium.”

(a)

State the nature of the metallic bond in terms of the particles involved.

[1]
(b)

Use Figure 1 to explain how the metallic model accounts for malleability.

[2]
(c)

Explain how the metallic model accounts for electrical conductivity.

[1]
(d)

Evaluate both inferences made by the student, using Figure 1 and the table.

[4]

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