A laboratory demonstration compares how a single crystal of sodium chloride and a strip of copper metal respond when compressed between two hard steel plates.
• The sodium chloride crystal breaks cleanly into multiple smaller pieces after only a small decrease in length.
• The copper strip widens and thins noticeably but remains in one piece even after a large overall reduction in length.
Use particulate-level reasoning to account for the different macroscopic behaviors of these two solids when the same type of compressive stress is applied.
(a) For each sample, identify the category of solid to which it belongs and state the primary type(s) of bonding or interaction that hold the particles together.
(b) Describe, in terms of particle positions and electrostatic interactions, what happens inside the sodium chloride lattice as the top layers of ions are forced to shift slightly relative to the bottom layers.
(c) Describe, in terms of particle positions and bonding, what happens inside the copper lattice as layers of atoms are forced to shift slightly relative to one another under the same compressive stress.
(d) Explain why the observed macroscopic outcome for sodium chloride is brittle fracture, whereas the outcome for copper is ductile deformation. Your explanation must explicitly connect the particulate descriptions from parts (b) and (c) to the macroscopic observations.
(e) After deformation, which sample—if either—is expected to have changed its ability to conduct electricity? Provide reasoning that relates electrical conductivity to the particle-level structure of each solid before and after compression.