Lewis Structures and Reactivity #1: The Case of Nitrogen Dioxide (NO2)

The Lewis structures of NO₂ were derived in a previous article entitled “Lewis Structures and the Octet Rule using a simple procedure. The structures indicate that NO₂ is an odd-electron molecule, a free radical as it is called. As a matter of fact the odd electron in the molecule appears to be somewhat local to the nitrogen atom.

Fig. 1: Resonance structures of nitrogen dioxide NO₂

 

The above resonance Lewis structures in a sense explain the reactivity of NO₂. As an odd electron species is expected to be very reactive trying either to get rid off or to find an extra electron so that it will become more stable (octet rule is obeyed in the last case). As a consequence, it readily reacts with another molecule of NO₂ to form a dimer, N₂O₄. The dimerization process (equilibrium) is so facile that it cannot be retained in pure form at ordinary temperatures.

    Fig. 2: Formation of N₂O₄  from NO2

The video below shows the eqiliburium that is readily established between NO₂ and N₂O₄