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 give the shape of each molecule, explain why each molecule has that shape and how the shape influences the forces that affect the melting point.

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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

Explain the shape of XeF₄

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Answer

The shape of XeF₄ is square planar due to the presence of four bonding pairs and two lone pairs of electrons around the xenon atom. This arrangement minimizes repulsion between the electron pairs, resulting in a square planar geometry.

Step 2

Explain the shape of PF₅

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Answer

The shape of PF₅ is trigonal bipyramidal. This is because phosphorus has five bonding pairs of electrons and no lone pairs, allowing for this arrangement to minimize repulsion between electron pairs.

Step 3

Discuss how the shapes influence the forces affecting melting points

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XeF₄, with its square planar shape, has a more significant dipole moment due to its asymmetry, resulting in stronger London dispersion forces and dipole-dipole interactions. Conversely, PF₅, being symmetrical in its trigonal bipyramidal shape, has a weaker net dipole moment, leading to weaker intermolecular forces. This difference in intermolecular forces is a key reason why XeF₄ has a higher melting point than PF₅.

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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

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

Explain the shape of XeF₄

Explain the shape of PF₅

Discuss how the shapes influence the forces affecting melting points

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