Why does iodine have a higher boiling point than CCl4? Iodine boils at 114 degrees celsius and carbon tetrachloride boils at -23 degrees Celsius.
Iodine, which is the diatomic molecule I2, has a higher boiling point than carbon tetrachloride, CCl4, because it has stronger intermolecular attractions. Intermolecular attractions are the forces of attraction between molecules. In order for a solid to melt or a liquid to vaporize enough energy must be absorbed to overcome these forces.
There are four types of intermolecular forces:
Dipole-dipole interactions - these forces are the result of attractions between positive and negative ends of polar molecules.
Ion-dipole interactions - these forces result from the attractions between ions and the oppositley charged regions of polar molecules.
Hydrogen bonds - these are very strong dipole-dipole interactions that occur between very polar molecules that have a hydrogen atom bonded to a fluorine, oxygen or nitrogen.
London dispersion forces - these interactions occur between all molecules regardless of polarity. They're caused by attractions between temporarily polar regions of molecules that arise when electrons are unevenly distributed. A temporary dipole on one molecule can induce one on another by attracting or repelling its electrons.
I2 and CCl4, being symmetrical and non-polar, have only London dispersion forces. The LDFs in I2 must be stronger than those in CCl4 in order for it to have a higher boiling point. This is the case because I2 has a very large electron cloud compared to CCl4 and is therefore more polarizable.
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