Samples of diamond, graphite, and cesium iodide (CsI) are available in the laboratory. A student is asked to investigate their mechanical properties and relate those observations to their particle-level structures.
(a) Rank the three solids in order of decreasing hardness (1 = hardest). Provide a brief justification for each placement that references the nature of bonding and dimensionality (if applicable) in the solid.
(b) Both diamond and graphite are composed solely of carbon atoms, yet their hardness differs dramatically. Explain this contrast in terms of lattice arrangement and the presence or absence of delocalized electrons.
(c) When a small stress is applied, CsI shatters rather than deforms. Using electrostatic arguments, explain why ionic lattices such as CsI are typically brittle.