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Radicals and VSEPR calculation for nitrogen dioxide, NO2

Another complication crops up when there are unpaired electrons. This is well illustrated for nitrogen dioxide. So, for NO2 there is an integral number of electrons but a non-integral number of electron pairs. Since any orbital can accommodate 0, 1, or 2 electrons, 21/2 electron pairs must be placed into three orbitals. Therefore the geometry is based upon a trigonal-planar arrangement of electron pairs. Since the lone-pair orbital is only half filled, it demands less space, and the O-N-O angle opens out a little (to 134.1°) from the ideal trigonal angle of 120°.

Addition of one electron to NO2 gives the nitrite anion NO2-. This last electron completes the half-occupied lone-pair orbital and this filling of the orbital causes it to fill out, and so close the O-N-O bond angle to 115°.

Nitrogen dioxide, NO2
Lewis structure: NO2.gif
Central atom nitrogen
Valence electrons on central atom: 5
2 terminal oxygens each contribute 1 electron in the two σ bonds: 2
Subtract two for the two electrons contributed by N to the two π bonds: -2
Total: 6
Divide by 2 to give electron pairs 21/2
21/2 electron pairs: trigonal geometry for the 21/2 shape-determining σ-framwork orbitals
NO2
The geometry of nitrogen dioxide, NO2. You can use your mouse to manipulate the molecule in the right hand "Jmol" image.

A VSEPR tutorial on the WWW

VSEPR tutorial on the WWW, URL: http://winter.group.shef.ac.uk/vsepr/
Copyright 1996-2015 Prof Mark Winter [The University of Sheffield]. All rights reserved.
Document served: Friday 24th March, 2017