Answer:
The vast difference in melting points between AlF3 (1291 °C) and PF3 (-151.5 °C) can be attributed to the nature of the bonding and intermolecular forces present in each compound.
* AlF3: Aluminum fluoride is an ionic compound. It consists of Al³⁺ cations and F⁻ anions. The strong electrostatic forces of attraction between these oppositely charged ions require a significant amount of energy to overcome, resulting in a very high melting point.
* PF3: Phosphorus trifluoride is a covalent compound. It has polar covalent bonds between the phosphorus atom and the fluorine atoms. However, these molecules experience weaker intermolecular forces compared to the ionic interactions in AlF3. These intermolecular forces, primarily dipole-dipole interactions, are easier to overcome, leading to a much lower melting point.
In essence, the strong ionic bonds in AlF3 require significantly more energy to break compared to the weaker intermolecular forces in PF3, resulting in the observed difference in melting point
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