Question

Which of the following compounds would you expect to show dispersion forces? Dipole forces? (a) \(\mathrm{F}_{2}\) (b) \(\mathrm{CO}\) (c) \(\mathrm{CO}_{2}\) (d) \(\mathrm{H}_{2} \mathrm{CO}\)

Short answer

Question: Identify the types of intermolecular forces present in each of the following compounds: (a) F2 (b) CO (c) CO2 (d) H2CO. Answer: (a) F2 has dispersion forces. (b) CO has both dispersion forces and dipole forces. (c) CO2 has dispersion forces. (d) H2CO has both dispersion forces and dipole forces.

Step-by-step solution

Compound (a) \(\mathrm{F}_{2}\)

Fluorine gas (\(\mathrm{F}_{2}\)) is a homonuclear diatomic molecule with both atoms being the same element (fluorine). Since there is no difference in electronegativity between the two fluorine atoms, the molecule is considered nonpolar. Nonpolar molecules exhibit dispersion forces only. So, \(\mathrm{F}_2\) shows dispersion forces.

Compound (b) \(\mathrm{CO}\)

Carbon monoxide (\(\mathrm{CO}\)) is a heteronuclear diatomic molecule with carbon and oxygen atoms. These two elements have different electronegativities, which results in a polar bond. Since the molecule is polar, it will exhibit dipole forces. Carbon monoxide also shows dispersion forces, as all molecules do.

Compound (c) \(\mathrm{CO}_{2}\)

Carbon dioxide (\(\mathrm{CO}_{2}\)) is a linear molecule with two polar C=O bonds. However, these bonds are symmetrically arranged around the central carbon atom, which cancels out the molecular dipole moment, making it nonpolar. As with all molecules, it will exhibit dispersion forces. So, \(\mathrm{CO}_2\) shows dispersion forces but not dipole forces.

Compound (d) \(\mathrm{H}_{2}\mathrm{CO}\)

Formaldehyde (\(\mathrm{H}_{2}\mathrm{CO}\)) is a planar molecule with each hydrogen atom bonded to the carbon atom, and a double bond between the carbon and oxygen atoms. The electronegativity difference between carbon and oxygen, as well as between hydrogen and carbon, results in a net molecular dipole moment, making it a polar molecule. So, \(\mathrm{H}_{2}\mathrm{CO}\) exhibits both dispersion forces and dipole forces.