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The p-Block Elements
Group 15: Anomalous Behaviour of Nitrogen
1 question from 1 paper, each with its answer.
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- paper
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- of The p-Block Elements
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Concepts tested
- Weak p-pi p-pi bonding in phosphorus
All Questions
2001 AIPMT 1 question
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Nitrogen forms $N_2$, but phosphorus forms $P_4$ instead of $P_2$; the reason is : -Nitrogen is small, so its 2p orbitals overlap well sideways and form strong $p\pi - p\pi$ bonds. It exists as $N\equiv N$.
Phosphorus atoms are larger, so the sideways overlap of their 3p orbitals is poor and $p\pi - p\pi$ bonds are weak.
So instead of forming a triple bond ($P\equiv P$), each phosphorus forms three single P–P bonds, giving the tetrahedral $P_4$ molecule.
So the reason is that $p\pi - p\pi$ bonding is weak in phosphorus.