Chemistry · Ch 9 — Elements of Group 13, 14 and 15
Nitric acid (HNO3)
Nitric acid (HNO3)
Nitric acid, HNO3, is a strong, oxidising mineral acid whose central nitrogen atom is sp2 hybridised. Its bonding cannot be captured by a single Lewis structure: the nitrogen-oxygen bonding is delocalised across two of the three N-O bonds, so HNO3 is best described as a resonance hybrid of two contributing structures in which the position of the N=O double bond and a formal positive charge on nitrogen shift between two of the oxygen atoms (see the HNO3-resonance figure note). Measured bond parameters reflect this delocalisation directly: the two resonance-averaged N-O bonds are of intermediate, near-equal length, with O-N-O bond angles around 120°-130° and an N-OH bond length of about 140.6 pm, rather …
What this figure shows. The diagram shows two resonance contributing structures of HNO3 side by side, connected by a resonance (double-headed) arrow: in one structure the N=O double bond and a formal positive charge on nitrogen sit on one terminal oxygen, and in the other structure they shift to the other terminal oxygen, with the N-OH single bond and its hydrogen fixed in both structures. Bond parameters are marked on the diagram to show the real molecule is an average of these two structures rather than either alone: a distance of about 96 pm associated with the O-H hydrogen, O-N-O bond angles of roughly 120° and 130°, and an N-OH bond length of about 140.6 pm, with partial (delta) positive/negative charge notation on the resonance-hybrid ox …