A solid substance E was heated gradually from 25 °C to 1400 °C while its electrical conductivity was monitored. The observations are summarized verbally:
• Between 25 °C and 750 °C the conductivity is essentially zero.
• At 800 °C the substance begins to melt, forming a liquid that conducts electricity well.
• Upon complete melting the conductivity increases by three orders of magnitude compared with the solid.
Additional information: The solid is brittle and cleaves along flat planes when struck lightly with a hammer.
(a) Based on the temperature-dependent conductivity data, estimate a plausible range for the melting point of substance E and justify your estimate.
(b) Identify the predominant bonding type present in substance E and explain how both the conductivity data and brittleness support your conclusion.
(c) Predict how the lattice energy of substance E compares qualitatively with that of a metallic solid of similar molar mass. Provide two factors that account for the difference.
(d) Describe an experiment, other than measuring conductivity, that could further confirm the bonding type you proposed for substance E. Specify the observable result expected if your bonding assignment is correct.