Which types of intermolecular forces are present in a sample of H2CO (formaldehyde)?

• A. Hydrogen bonding and dipole-dipole interactions
• B. London dispersion forces and dipole-dipole interactions
• C. London dispersion forces only
• D. Hydrogen bonding only

Answer: (B)

Verified step by step guidance

1. Identify the molecular structure of formaldehyde (H2CO). It consists of a carbon atom double bonded to oxygen and single bonded to two hydrogen atoms.
2. Determine the polarity of the molecule. Since oxygen is more electronegative than carbon and hydrogen, the C=O bond is polar, making the molecule polar overall.
3. Recognize that polar molecules exhibit dipole-dipole interactions due to the attraction between partial positive and partial negative charges on different molecules.
4. Check for the presence of hydrogen bonding. Hydrogen bonding occurs when hydrogen is directly bonded to highly electronegative atoms like N, O, or F. In formaldehyde, hydrogen is bonded to carbon, not oxygen, so hydrogen bonding is not present.
5. Remember that all molecules, regardless of polarity, exhibit London dispersion forces due to temporary fluctuations in electron density creating instantaneous dipoles.