The table below lists four solids along with selected experimental data collected at 298 K
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
The table below lists four solids along with selected experimental data collected at 298 K.
Solid
ΔH_sub (kJ mol⁻¹)
σ_solid (S m⁻¹)
σ_molten (S m⁻¹)
Diamond (C)
716
1.0 ×10⁻¹²
— (does not melt below decomposition)
Graphite (C)
716
2.5 ×10³
6.0 ×10³
Sodium chloride
171
1.0 ×10⁻⁹
3.0 ×10²
Solid xenon
12
1.0 ×10⁻¹²
— (gas upon melting)
ΔH_sub is the enthalpy of sublimation (energy required to convert the solid directly to gas). σ denotes electrical conductivity; a dash indicates that the substance decomposes or vaporizes before reaching a molten state.
Using the data provided, answer the following questions.
(a) Classify each solid as metallic, ionic, molecular, or covalent network. Provide evidence from the data to support each classification.
(b) For diamond and graphite, the ΔH_sub values are identical, yet their conductivities differ by many orders of magnitude. Explain this discrepancy in terms of atomic bonding and electron distribution.
(c) Using your classifications from part (a), rank the four solids from greatest to least strength of the forces holding the particles together in the solid state. Justify your ranking with reference to both ΔH_sub and type of bonding.
(d) Sodium chloride exhibits a dramatic increase in conductivity upon melting, whereas graphite does not. Account for this difference by discussing the identity of mobile charge carriers in each case.