Boiling points London dispersion force

A. Alkanes are composed entirely of non-polar C-C and C-H bonds, resulting in no dipole interactions or hydrogen bonding. London dispersion forces increase with the size of the molecule, resulting in a higher temperature requirement to break these bonds and a higher boiling point. 

Intermolecular forces Intramolecular forces Dipole-dipole attraction Hydrogen bonding London dispersion forces Normal boiling point Heating/cooling curve Normal freezing point Molar heat of fusion Molar heat of vaporization... 

As the molecular weight increases from Cl to 1, the greater the London dispersion forces present, which will increase the boiling point as observed. However, HF is the only compound listed that has the ability to form hydrogen bonds, which explains the anomaly in the trend. 

With the exception of ammonia, water and hydrogen fluoride, hydrogen bonds are not present in the hydrides of elements in groups 15, 16 and 17. The increase in the boiling points for the hydrides of each periodic group is therefore due to the increase in London (dispersion) forces as the molecular size increases. 

The boiling points of ammonia, water and hydrogen fluoride are anomalously high compared to those of the hydrides of other elements in groups 15, 16 and 17 of the periodic table. This is evidence for the existence of hydrogen bonds which are appreciably stronger than the London (dispersion) forces that exist between molecules. 

Since the hydrocarbon chains are often very long, the London (dispersion) forces between the chains are often very strong and the polymers have relatively high melting and boiling points. 

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