Explicit science instruction
Polar molecules can align partially so opposite partial charges attract; this adds dipole–dipole interactions to dispersion.
Hydrogen bonding is a particularly strong, directional intermolecular interaction involving H bonded to N, O, or F interacting with a suitable lone-pair site.
A molecule capable of hydrogen bonding still experiences dispersion and may also experience ordinary dipole–dipole attraction.
Vocabulary: dipole–dipole; hydrogen bonding; donor; acceptor; partial charge.
Worked example with reasoning
CH₃OH can hydrogen-bond because it contains an O–H bond and oxygen lone pairs. CH₃OCH₃ has polar C–O bonds and lone pairs but no O–H donor, so its intermolecular interaction pattern differs.
Guided question
Why can methanol and dimethyl ether have different boiling behavior despite the same molecular formula? Use interaction evidence.
Independent work
- Identify the strongest relevant IMF for five supplied molecules.
- Mark hydrogen-bond donor and acceptor sites.
- Explain why 'strongest IMF' does not mean other attractions disappear.
Misconception check
Hydrogen bonding is not a covalent bond between two molecules; it is an intermolecular attraction.
Formative understanding check
What structural feature is required for a molecule to donate a conventional hydrogen bond?
Reveal response
Hydrogen must be covalently bonded to a strongly electronegative atom such as N, O, or F.
Mentor evidence conference
Ask Archaemenes to test whether your structure–property claim controls competing variables.
Teacher guidance
Foundation: Identify interaction types from structures.
Core: Explain relative IMF patterns using polarity and donor/acceptor structure.
Extended: Analyze molecules with multiple competing interaction sites.