In $NO_3^-$ ion number of bond pairs and lone pairs of electrons on nitrogen atom are : -
A
2, 2
B
3, 1
C
1, 3
D
4, 0
The answer is D.
Solution
Lewis structure of $NO_3^-$: N is joined to one O by a double bond and to two O atoms by single bonds; the ion has 24 valence electrons. Around nitrogen: one N=O double bond (2 bond pairs) + two N–O single bonds (2 bond pairs) = 4 bond pairs. Nitrogen uses all 5 of its valence electrons plus the extra charge in bonding (one N–O bond is a coordinate bond), so it has no lone pair. Hence N has 4 bond pairs and 0 lone pairs. (Its shape is trigonal planar, since only the 3 $\sigma$ bonds decide the shape.)
ConceptBond pairs and lone pairs around N in nitrate
Chemical Bonding and Molecular Structure in past papers
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