Lewis dot structure of carbonic acid H2CO3

A simple procedure for writing electron Lewis dot structures was given in a previous post 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 examine the case of carbonic acid H₂CO₃. How can we draw the carbonic acid Lewis dot structure?

Step 1: Connect the atoms with single bonds. 

Fig. 1 : Connect the atoms of carbonic acid with single bonds

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

Where n in this case is 4 since H₂CO₃ consists of six atoms but two of them are H atoms.

Where V = (1 + 6 + 4 + 6 + 6 + 1) = 24 

Therefore, P = 6n + 2 – V = 6 * 4 + 2 – 24 = 2      So  there are 2 π electrons in H₂CO₃and therefore 1 double bond must be added to the structure of Step 1.

Step 3 & 4: The Lewis structure of H₂CO₃  is derived below:

Fig. 2: Lewis structure of carbonic acid H2CO3