Group 15 Hydrides
Mediumchemistry
Boiling point trend of Group 15 hydrides (NH3, PH3, AsH3, SbH3) mainly influenced by:
Select the correct option:
Solution
Incorrect! Answer:
Hydrogen bonding in NH3
- Normal Trend: Boiling points usually increase down a group as atomic size/mass increases because van der Waals forces (dispersion forces) become stronger.
- Expected vs Actual: One would expect NH3 to have the lowest boiling point, but it actually boils much higher than PH3 and AsH3.
- The Anomaly: This is due to inter-molecular Hydrogen bonding in NH3. Nitrogen is highly electronegative and the N2˘013H bond is strongly polar.
- Pattern: PH3<AsH3<NH3<SbH3<BiH3. NH3 is 'out of line' because of the strong attractive forces between its molecules.
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About This Question
- Subject
- chemistry
- Chapter
- p-block elements
- Topic
- group 15 hydrides
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Hydrogen bonding in NH3
- Normal Trend: Boiling points usually increase down a group as atomic size/mass increases because van der Waals forces (dispersion forces) become stronger.
- Expected vs Actual: One would expect NH3 to have the lowest boiling point, but it actually boils much higher than PH3 and AsH3.
- The Anomaly: This is due to inter-molecular Hydrogen bonding in NH3. Nitrogen is highly electronegative and the N2˘013H bond is strongly polar.
- Pattern: PH3<AsH3<NH3<SbH3<BiH3. NH3 is 'out of line' because of the strong attractive forces between its molecules.
This medium difficulty chemistry question is from the chapter p-block elements, covering the topic of group 15 hydrides. It appeared in the 2025 exam.
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