Given the following melting points in ^∘ C, estimate the value for CBr4: CF4,-184 ; CCl4,-23 ;

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Given the following melting points in ^∘ C, estimate the...

Given the following melting points in ${ }^{\circ} \mathrm{C}$, estimate the value for $\mathrm{CBr}_{4}: \mathrm{CF}_{4},-184 ; \mathrm{CCl}_{4},-23 ; \mathrm{CI}_{4}, 171$ (decomposes). Using a reference other than your textbook, look up the melting point of $\mathrm{CBr}_{4}$. How does your predicted value compare with the reported value?

Given the following melting points in ${ }^{\circ} \mathrm{C}$, estimate the value for $\mathrm{CBr}_{4}: \mathrm{CF}_{4},-184 ; \mathrm{CCl}_{4},-23 ; \mathrm{CI}_{4}, 171$
(decomposes). Using a reference other than your textbook, look up the melting point of $\mathrm{CBr}_{4}$. How does your predicted value compare with the reported value?

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Key Concepts

Molecular Structure and Packing

The symmetry and geometry of molecules influence how they pack in the solid state. In tetrahalides, the spherical or tetrahedral shape allows for efficient packing, which affects the lattice energy and thus the melting point. Variations in the size and nature of the substituent halogens alter the packing efficiency, thereby impacting the phase transition temperatures.

Periodic Trends in Halogen Properties

Periodic trends such as increasing atomic size and polarizability down the halogen group explain the progression in melting points. As one moves from fluorine to iodine, the increased mass and electron cloud size enhance the strength of intermolecular interactions in tetrahalides. This trend is key to predicting and understanding the melting point of compounds like CBr4 in comparison to CF4, CCl4, and CI4.

Intermolecular Forces

Intermolecular forces, particularly London dispersion forces, are key in determining the melting points of molecular compounds. These forces arise from temporary induced dipoles in molecules and increase in strength as the electron clouds become more polarizable. For tetrahalides, as the halogen atoms become larger and more polarizable, the dispersion forces become stronger, which in turn raises the melting point.

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