What is the predominant intermolecular force in CH3NH2?
The correct answer and explanation is:
The predominant intermolecular force in CH₃NH₂ (methylamine) is hydrogen bonding.
Explanation:
CH₃NH₂, methylamine, is an organic molecule with the formula CH₃–NH₂. It contains a nitrogen atom bonded to hydrogen atoms and a methyl group (CH₃). Understanding the intermolecular forces in methylamine involves looking at the types of interactions between molecules:
- Hydrogen Bonding
The nitrogen atom in CH₃NH₂ is highly electronegative and bonded to hydrogen atoms. This creates a significant dipole where the hydrogen atoms attached to nitrogen have a partial positive charge (δ+), and the nitrogen has a partial negative charge (δ–).
Because nitrogen has a lone pair of electrons and is bonded to hydrogen, methylamine molecules can form strong hydrogen bonds between the hydrogen of one molecule’s –NH₂ group and the lone pair on the nitrogen of another molecule.
Hydrogen bonding is a strong type of dipole-dipole interaction and is stronger than regular dipole forces or London dispersion forces. - Dipole-Dipole Interactions
Methylamine is a polar molecule due to the difference in electronegativity between nitrogen and carbon/hydrogen atoms. This polarity causes dipole-dipole attractions between molecules, but these are less strong compared to hydrogen bonding. - London Dispersion Forces (Van der Waals forces)
All molecules exhibit London dispersion forces, which arise from temporary fluctuations in electron distribution. However, these forces are the weakest of the intermolecular forces and are not the main contributors in methylamine.
Summary:
- The presence of N–H bonds and the nitrogen lone pair enables hydrogen bonding.
- Hydrogen bonding dominates over dipole-dipole and dispersion forces in methylamine.
- This hydrogen bonding is responsible for methylamine’s relatively high boiling point compared to molecules of similar molecular weight without hydrogen bonding.
In conclusion, the predominant intermolecular force in CH₃NH₂ is hydrogen bonding, due to the N–H bonds and the nitrogen’s lone pair enabling strong intermolecular attractions between molecules.