Simple Method for writing Lewis Structures of the Oxalate ion C2O4-2 -#12

A simple procedure for writing Lewis structures is given in a previous article entitled “Lewis Structures and the Octet Rule”. Relevant worked examples were given in the following articles: Examples #1, #2, #3 , #4, #5, #6,  #7,  #8, #9, #10 and #11. 

Another example  for writing Lewis structures following the above procedure is given bellow:

 Let us consider the case of oxalate ion (C₂O₄^-2). Oxalate is a dianion that forms coordination compounds acting as a ligand. Many metal ions form insoluble precipitates with oxalate, a prominent example is calcium oxalate, a primary constituent of kidney stones.  

 

Step 1: Connect the atoms with single bonds

Fig. 1: Connecting the atoms of the oxalate ion C₂O₄^-2 with single bonds

Step 2: Calculate the # of electrons in πbonds (multiple bonds) using  formula (1) in the article entitled “Lewis Structures and the Octet Rule”. 

:

Where n in this case is 6 since  C₂O₄^-2  consists of six atoms.

Where V = (4 + 6 + 6 + 4 + 6 |+ 6) – (-2) = 34  

Therefore, P = 6n + 2 – V = 6 * 6 + 2 – 34 = 4   \  there are 4 π electrons in C₂O₄^-2  \

2 double bonds or 1 triple bond must be added to the structure of Step 1.

Step 3 & 4: The Lewis structures for C₂O₄^-2 are as follows: