A chemist investigates a series of binary compounds of a metal M with the halogens F, Cl
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
A chemist investigates a series of binary compounds of a metal M with the halogens F, Cl, and Br. The compounds are labeled MF, MCl, and MBr. Selected macroscopic properties are listed below.
Property | MF | MCl | MBr
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Melting point / °C | 1410 | 971 | 732
Enthalpy of fusion / kJ mol−1 | 28 | 22 | 17
Electrical conductivity (solid) | None | None | None
Electrical conductivity (molten) | High | High | High
Solubility in water (25 °C) / g per 100 g H2O | 55 | 38 | 18
(a) Rank the three compounds in order of increasing ionic character. Justify your ranking using the data in the table.
(b) The chemist measures the lattice energy of each compound indirectly via a Born–Haber cycle. Predict which compound has the largest magnitude of lattice energy and explain your reasoning.
(c) Explain why none of the three solids conducts electricity in the solid state even though they conduct when molten.
(d) Suppose a new compound MI is synthesized with the same crystal structure as MF, MCl, and MBr. Predict qualitative values (higher, lower, or similar) for its melting point and solubility in water relative to MBr, and justify each prediction by referencing periodic trends and bonding considerations.