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The Metallic Model · Paper 2 — Free Chemistry HL Practice Questions

1ChallengeSAQ-LMetallic bonding and electron sea model8 marksPaper 2~12 min

Data

Conductivity of copper at 298 K=5.96×107 S m−1298\,\text{K} = 5.96 \times 10^{7}\,\text{S\,m}^{-1}; conductivity of brass (70%70\% Cu, 30%30\% Zn) at 298 K=1.50×107 S m−1298\,\text{K} = 1.50 \times 10^{7}\,\text{S\,m}^{-1}.
The electron sea model describes metallic bonding as a lattice of positive ions surrounded by a sea of delocalized electrons. This model can be used to explain many properties of metals and alloys.
(a)
Explain, using the electron sea model, why pure copper has a higher electrical conductivity than brass. [3 marks]
(b)
The melting point of sodium is 97.8 °C97.8\,°\text{C}, while the melting point of magnesium is 650 °C650\,°\text{C}. Using the electron sea model, explain this difference in melting points. [2 marks]
(c)
A student claims: "Alloying a pure metal always reduces its malleability." Evaluate this claim using the electron sea model, referring to the effect of atomic radius difference between the host and solute metal. [3 marks]

Solutions

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