The University of Sheffield 
Department of Chemistry 
VSEPR 
Radicals and VSEPR calculation for nitrogen dioxide, NO_{2}
Another complication crops up when there are unpaired electrons. This is well illustrated for nitrogen dioxide. So, for NO_{2} there is an integral number of electrons but a nonintegral number of electron pairs. Since any orbital can accommodate 0, 1, or 2 electrons, 2^{1}/_{2} electron pairs must be placed into three orbitals. Therefore the geometry is based upon a trigonalplanar arrangement of electron pairs. Since the lonepair orbital is only half filled, it demands less space, and the ONO angle opens out a little (to 134.1°) from the ideal trigonal angle of 120°.
Addition of one electron to NO_{2} gives the nitrite anion NO_{2}^{}. This last electron completes the halfoccupied lonepair orbital and this filling of the orbital causes it to fill out, and so close the ONO bond angle to 115°.
Nitrogen dioxide, NO_{2}
Lewis structure: 

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 
2^{1}/_{2} 
2^{1}/_{2} electron pairs: 
trigonal geometry for the 2^{1}/_{2} shapedetermining σframwork orbitals 


The geometry of nitrogen dioxide, NO_{2}. You can use your mouse to manipulate the molecule in the right hand "Jmol" image. 
