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:
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

The geometry of nitrogen dioxide, NO2. You can use your mouse to manipulate the molecule in the right hand "Jmol" image.