CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Four crystalline solids, labeled A–D, are investigated. Their measured properties are summarized in the table.
Property
A
B
C
D
Melting point (°C)
>3500
660
801
3900
Vickers hardness (GPa)
0.10
3.0
0.02
70
Electrical conductivity
Good
Excellent
None (solid)
None (solid)
Cleavage energy (kJ mol⁻¹)
0.25
1.5
3.0
12
(The conductivity entry “None (solid)” indicates the substance does not conduct electricity in the solid state.)
(a) For each solid, identify the most likely structural type from the following list and justify your assignments by citing two pieces of evidence from the table for each choice.
• Layered covalent network of carbon atoms (graphite-like)
• Metallic element (copper-like)
• Ionic compound composed of Na⁺ and Cl⁻ ions (sodium chloride-like)
• Three-dimensional covalent network of carbon atoms (diamond-like)
(b) For the solid you identified as graphite-like, state two industrial or technological applications that exploit its structure-dependent properties, and explain the connection between each property and its underlying bonding.
(c) Diamond is often described as both extremely hard and brittle. Using the structural information you inferred from the table, reconcile these two seemingly opposing mechanical descriptors.