posted by eliz on .
How do you determine what molecule will have the highest or lowest boiling points.
example: if you had CH3F, N2H4, CH3OH and O2. how would you determine what is the highest boiling points? What do you look at?
Read about intermolecular forces.
Two things in particular.
In general, the boiling point is higher for more mass which just means adding to obtain the molar mass and checking that one for the higher boiling point. For isomers with the same mass, the more compact ones tend to boil at a lower temperature. For example, n-butane you would expect to be higher boiling than tetramethyl methane.
The second thing is hydrogen bonding. Hydrogen bonding makes the boiling point much higher than would be expected, even for lower molecular mass molecules. Hydrogen bonding is always something to consider with the elements with higher electronegativity such as N, F, and O. I see three of the molecules have that but I would expect H bonding to be more of a factor with CH3OH than CH3F. The electronegativity of N is less than that of O. O2 is not polar and you would expect it to have a lower boiling point than any of the otherrs.