A materials scientist is comparing two newly synthesized solids, X and Y, whose macroscopic properties are summarized in the table below.
Property Solid X Solid Y
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Melting point ≈ 3 600 K ≈ 800 K
Hardness Resists scratching Easily indented
Electrical conductivity (25 °C) None High
Thermal conductivity (25 °C) High High
After initial characterization, the scientist is surprised by Solid Y’s combination of a relatively low melting point and high electrical conductivity.
(a) For each solid, classify the most likely bonding/structural type (ionic, molecular, metallic, or covalent network). Justify your classifications using at least two properties from the table for each solid.
(b) Solid Y appears soft despite its high electrical and thermal conductivities. Propose a plausible structural explanation for this combination of properties, referencing atomic-level features of the lattice.
(c) Predict whether Solid X would be expected to conduct electricity when molten. Justify your prediction with reference to the arrangement and mobility of charge carriers at the elevated temperature.