How do I rank the following compounds from lowest to highest boiling point: calcium carbonate, methane, methanol (CH₄O), dimethyl ether (CH₃OCH₃)?

1 Answer
Ernest Z.
May 17, 2014

The order of boiling points is: CH4<CH3OCH3<CH4O<CaCO3

Explanation:

The order of strengths of intermolecular forces is: ion-ion > H-bonding > dipole-dipole > London dispersion.

Compounds with stronger intermolecular forces have higher boiling points.

The strongest intermolecular force in each of the compounds is:

CaCO3 — ion-ion attractions.
CH4 — London dispersion forces
CH3OH — hydrogen bonding
CH3OCH3 — dipole-dipole attractions

CaCO3 is an ionic compound. It has the highest boiling points

Next comes methanol, CH4O or CH3OH.

Methanol has strong hydrogen bonds. It will have the next highest boiling point.

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Dimethyl ether, CH3OCH3, is a polar molecule.

The C-O bond dipoles reinforce each other, so the molecule has a dipole moment.

Dipole-dipole forces are not as strong as hydrogen bonds, so dimethyl ether has a lower boiling point than methanol does.

Finally, the C-H bonds in methane are nonpolar, so the molecule is also nonpolar.

It has only weak London dispersion forces,

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CH4, has the lowest boiling point.

The order of boiling points is:

CH4<CH3OCH3<CH4O<CaCO3

Here's a good video on ordering compounds according to their intermolecular forces and boiling points.

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