What types of intermolecular forces exist between NH3 and HF?
A) dispersion forces and hydrogen bonds
B) dispersion forces
C) dispersion forces and dipole-dipole forces
D) dispersion forces, dipole-dipole forces, and hydrogen bonds
E) dispersion forces, hydrogen bonds, and ion-dipole forces
The correct answer and explanation is :
The correct answer is:
D) Dispersion forces, dipole-dipole forces, and hydrogen bonds
Explanation:
Intermolecular forces are the attractive forces that exist between molecules. When considering the interaction between ammonia (NH₃) and hydrogen fluoride (HF), we need to analyze the types of forces that can occur:
- Dispersion Forces (London Forces):
- These forces are present in all molecules, regardless of their polarity.
- They arise due to temporary fluctuations in electron distribution, which create instantaneous dipoles.
- Even though NH₃ and HF are both polar molecules, they still experience dispersion forces as a weak intermolecular attraction.
- Dipole-Dipole Forces:
- Both NH₃ and HF are polar molecules because they have permanent dipoles.
- NH₃ has a trigonal pyramidal shape with a partial negative charge on nitrogen and partial positive charges on hydrogen.
- HF has a strong dipole due to the high electronegativity of fluorine, making it highly polar.
- The partial positive charge of NH₃ (on hydrogen) attracts the partial negative charge of HF (on fluorine), leading to dipole-dipole interactions.
- Hydrogen Bonding:
- Hydrogen bonding is a special type of dipole-dipole interaction that occurs when hydrogen is directly bonded to nitrogen (N), oxygen (O), or fluorine (F), the three most electronegative elements.
- In NH₃, nitrogen has a lone pair and hydrogen atoms attached, allowing it to form hydrogen bonds.
- In HF, fluorine is highly electronegative and can form strong hydrogen bonds.
- Thus, NH₃ and HF can form hydrogen bonds with each other, where the hydrogen of one molecule interacts with the lone pair of another.
Why Other Choices Are Incorrect:
- A) Only dispersion forces and hydrogen bonds → Incorrect because dipole-dipole forces also exist.
- B) Only dispersion forces → Incorrect because strong dipole-dipole and hydrogen bonds are present.
- C) Only dispersion and dipole-dipole forces → Incorrect because hydrogen bonding is also significant.
- E) Including ion-dipole forces → Incorrect because there are no ions involved in NH₃ and HF interactions.
Thus, the correct answer is D) Dispersion forces, dipole-dipole forces, and hydrogen bonds.