What intermolecular forces are present in pure samples of both CH₃CH₂OH and CH₃CH₂NH₂?
A) Dispersion forces, dipole-dipole forces, and hydrogen bonding.
B) Dipole-dipole forces only.
C) Dipole-dipole forces and hydrogen bonding.
D) Dispersion forces and dipole-dipole forces
The Correct Answer and Explanation is:
Correct Answer:
A) Dispersion forces, dipole-dipole forces, and hydrogen bonding.
Explanation:
Intermolecular forces (IMFs) describe the attractions between molecules and determine physical properties like boiling point, melting point, and solubility. The types of intermolecular forces in a substance depend on its molecular structure and the presence of specific functional groups. Here’s a breakdown for CH₃CH₂OH (ethanol) and CH₃CH₂NH₂ (ethylamine):
1. Dispersion Forces
These forces, also known as London dispersion forces, exist in all molecules due to temporary fluctuations in electron density that create instantaneous dipoles. Both CH₃CH₂OH and CH₃CH₂NH₂ have dispersion forces because they contain electrons that can induce these temporary dipoles. Dispersion forces are the weakest intermolecular force but are always present.
2. Dipole-Dipole Forces
These forces occur in polar molecules, where permanent dipoles arise due to uneven distribution of electron density.
- CH₃CH₂OH has a polar hydroxyl group (-OH), making the molecule polar.
- CH₃CH₂NH₂ has a polar amine group (-NH₂), which also makes it polar.
Thus, dipole-dipole interactions exist in both molecules, as the dipoles align themselves to maximize attractive interactions.
3. Hydrogen Bonding
Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is covalently bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine.
- CH₃CH₂OH can form hydrogen bonds due to the highly electronegative oxygen in the -OH group.
- CH₃CH₂NH₂ can form hydrogen bonds due to the highly electronegative nitrogen in the -NH₂ group.
In both molecules, the hydrogen atoms attached to O or N participate in hydrogen bonding with neighboring molecules.
Summary
Both CH₃CH₂OH and CH₃CH₂NH₂ exhibit dispersion forces, dipole-dipole forces, and hydrogen bonding, making A the correct answer. These IMFs account for their relatively high boiling points compared to nonpolar molecules of similar molar mass.