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The melting point of XeF₄ is higher than the melting point of PF₅ - AQA - A-Level Chemistry - Question 7 - 2020 - Paper 1
Question 7
The melting point of XeF₄ is higher than the melting point of PF₅. Explain why the melting points of these two compounds are different. In your answer you should g... show full transcript
Worked Solution & Example Answer:The melting point of XeF₄ is higher than the melting point of PF₅ - AQA - A-Level Chemistry - Question 7 - 2020 - Paper 1
Step 1
Shape of XeF₄
Answer
The shape of XeF₄ (Xenon Tetrafluoride) is square planar. This geometry arises from the presence of four bonded fluorine atoms and two lone pairs of electrons on the xenon atom. The lone pairs occupy equatorial positions, leading to a symmetrical arrangement of the fluorine atoms.
Step 2
Step 3
Influence of Shape on Melting Points
Answer
The melting point of a substance is influenced by the strength of intermolecular forces. XeF₄, being square planar, can align its molecules more effectively, allowing for stronger London dispersion forces due to a larger electron cloud compared to PF₅. Additionally, the lone pairs in XeF₄ create a more significant repulsion affecting molecular arrangement, contributing to its higher melting point. Conversely, PF₅, with a trigonal bipyramidal shape, has weaker dipole interactions and does not align as effectively, resulting in a lower melting point.