Dot Structures|Lewis Structures - General Method for drawing -#33A: C2-2

An Easy Method for Constructing Dot Structures - Example: The Dicarbide ion  C₂^-2

A simple procedure for writing Lewis structures is 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   C₂^-2.

Step 1: Connect the atoms with single bonds. 

Fig. 1: Connecting  the atoms of  C₂^-2 with single bonds (Step 1 of the method) 

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

Where n in this case is 2 since C₂^-2  consists of 2 atoms.

Calculate the number of the valence electons (V) of  C₂^-2 :
Where V = 2*4 – (-2)  = 10

Therefore, P = 6n + 2 – V = 6 *2 + 2 – 10 = 4   Therefore, there are either 2 double bonds or 1 triple  bond.

The structure in Figure 1 cannot have 2 double bonds. The only possibility is 1 triple bond.

Step 3 & 4: The Lewis dot structure of  C₂^-2 is as follows:

Fig.1: Lewis structure of dicarbide  C2-2