Group 15 Nitrogen
Nitrogen exists as a diatomic gas with a very high bond dissociation enthalpy; what structural feature gives N_2 this exceptional stability?
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Solution
A triple bond with one sigma and two pi bonds
The stability of the nitrogen molecule arises from the strong multiple bond between its two atoms. In N_2 the two nitrogen atoms are joined by a triple bond consisting of one sigma bond and two pi bonds, formed by effective overlap of their 2p orbitals because of nitrogen's small size. This triple bond gives an extremely high bond dissociation enthalpy of about 941 kJ/mol, making molecular nitrogen remarkably inert at ordinary temperatures. The option of a single bond would give far lower stability and higher reactivity. The option of a double bond underestimates the actual bond order of three. The option of ionic interaction does not apply to a homonuclear non-metal molecule. This strong triple bond explains why nitrogen is unreactive and why nitrogen fixation requires harsh conditions, a key NCERT point. Plausibility check: the very high dissociation energy and the short N-N bond length are both consistent with a triple bond, confirming the structural explanation.
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About This Question
- Subject
- chemistry
- Chapter
- p-block elements
- Topic
- group 15 nitrogen
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
A triple bond with one sigma and two pi bonds
The stability of the nitrogen molecule arises from the strong multiple bond between its two atoms. In N_2 the two nitrogen atoms are joined by a triple bond consisting of one sigma bond and two pi bonds, formed by effective overlap of their 2p orbitals because of nitrogen's small size. This triple bond gives an extremely high bond dissociation enthalpy of about 941 kJ/mol, making molecular nitrogen remarkably inert at ordinary temperatures. The option of a single bond would give far lower stability and higher reactivity. The option of a double bond underestimates the actual bond order of three. The option of ionic interaction does not apply to a homonuclear non-metal molecule. This strong triple bond explains why nitrogen is unreactive and why nitrogen fixation requires harsh conditions, a key NCERT point. Plausibility check: the very high dissociation energy and the short N-N bond length are both consistent with a triple bond, confirming the structural explanation.
This easy difficulty chemistry question is from the chapter p-block elements, covering the topic of group 15 nitrogen. It appeared in the 2025 exam.
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