Question

How do you account for the boiling points of methane, ethane, methanol, and ethanol?

Answer 1

Consider the degree of INTERMOLECULAR force that operates between each substance....

Explanation:

But first, as chemists, as physical scientists, we should quote some data, and the normal boiling point is the best metric to assess intermolecular force...

`"methane, -164"` `""^@C;`

`"ethane, -89"` `""^@C;`

`"methanol, +64.7"` `""^@C;`

`"ethanol, +78.4"` `""^@C;`

So what have the alcohols got that the alkanes ain't got? And clearly the answer is the hydroxyl group which affords the phenomenon of intermolecular hydrogen bonding. The hydrogen is bound to a strongly electronegative element, i.e. oxygen, such that charge separation occurs, and the resultant dipoles line up intermolecularly....`R-O-stackrel(delta+)Hcdotsstackrel(-delta)O(H)-R`; this constitutes a potent intermolecular force of attraction, that is even more pronounced in the water molecule, of lower molecular mass, but even higher normal boiling point.