Canonical Structure| Lewis Structure of OCN- #45

A simple procedure for writing Lewis Structures was given in a previous article entitled “Lewis Structures and the Octet Rule”. Several worked examples relevant to this procedure were given in previous posts please see the Sitemap - Table of Contents (Lewis Electron Dot Structures).

Let us consider the case of  OCN^- 

Step 1: Connect the atoms with single bonds. 

Fig. 1 : Connect the atoms of  OCN^- with single bonds.

 Step 2:  Calculate the # of electrons in π bonds (multiple bonds) using  formula (1): 

Where n in this case is 3. Where V = (6 + 4 + 5) – (-1) = 16 , V is the number of valence electrons of the molecule.

Therefore, P = 6n + 2 – V = 6 * 3 + 2 – 16  = 4    So, there are :  2 double bonds or a triple bond.

Step 3 & 4: The   resonance structures of  OCN^-  are as follows:

Fig. 2 : Lewis resonance structures of  OCN^-

 

Structures #1 and #3 are more stable due to less charge separation comparing to #2. Structure #3 is more plausible than #1 since the more electronegative O atom has the negative charge. Therefore stability decreases:   #3 > #1 > #2

The most plausible electron dot structure (EDOTS) is #3 and the least plausible #2.