Five research teams independently characterized unknown crystalline solids labeled W, X, Y, Z, and M. Selected experimental results are provided below.
1. Differential scanning calorimetry reveals that W undergoes a sharp endotherm at –23∘C, while no additional endotherms are observed up to 300∘C.
2. Four-probe resistivity measurements show that X has a resistivity of 1.8×10–8Ωm that increases slightly with temperature.
3. Y is transparent; Raman spectroscopy shows broad peaks characteristic of strong covalent bonds in a continuous three-dimensional lattice.
4. Z conducts electricity when molten but not when solid; grinding Z between glass slides produces a powder that crumbles easily.
5. M remains ductile but its hardness is greater than that of pure copper; X-ray diffraction indicates that the crystal lattice contains two metallic elements of similar atomic radii in random positions.
Use the information above to analyze the solids.
(a) Assign a classification (ionic solid, covalent network solid, molecular solid, metallic solid, or alloy) to each of the five unknowns (W, X, Y, Z, and M).
(b) Construct a coherent argument, citing at least ONE experimental observation for EACH solid, that supports every classification you made in part (a).
(c) For two of the solids you classified, predict a macroscopic property NOT listed in the stimulus that would be consistent with their structures, and justify each prediction.
(d) Suppose subsequent analysis shows that W actually sublimes slowly at room temperature. Discuss how this additional observation might refine or alter your original classification, and propose one further experiment that could resolve any remaining ambiguity.