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The 'inert' gas that isn't: xenon compounds

Shapes of noble-gas compounds, IE trends, bond enthalpy from ΔfH, energetics of decomposition

In 1962 the first noble-gas compound was made. Xenon now forms

\ce{XeF2}

\ce{XeF4}

and the dangerously explosive solid

\ce{XeO3}

. First ionisation energies (kJ mol

^{-1}

): He 2372, Ne 2081, Ar 1521, Kr 1351, Xe 1170.

\Delta_fH

(kJ mol

^{-1}

\ce{XeF2(g)}

−108;

\ce{XeF4(g)}

−206;

\ce{XeO3(s)}

+402. Bond enthalpy F–F = 158 kJ mol

^{-1}

Facts you may need

Draw Lewis diagrams for

\ce{XeF2}

and

\ce{XeO3}

(each Xe=O as a double bond). Give the shape of each and state whether each molecule is polar.

Justify, using the ionisation energy data, why xenon forms compounds but helium, neon and argon do not.

Calculate the average Xe–F bond enthalpy from the data for

\ce{XeF2}

, and again from

\ce{XeF4}

. Comment on your results.

\ce{XeO3}

explodes violently:

\ce{2XeO3(s) -> 2Xe(g) + 3O2(g)}

. Discuss why this decomposition is so favourable, calculating

\Delta_rH

and considering both entropy terms, and suggest why

\ce{XeO3}

can nevertheless be stored briefly when dry.