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, #11, #12, #13, #14, #15, #16, #17, #18, #19, #20 and #21.
Another example for writing Lewis structures following the above procedure is given bellow:
Let us consider the case of dinitrogen tetroxide (N2O4).
Step 1: Connect the atoms with single bonds. The central atoms are the nitrogen atoms.
Where n in this case is 6 since N2O2 consists of six atoms.
Where V = (6 + 5 + 5 + 6 + 6 + 6 ) = 34, where V the number of the valence electrons of N2O2
Therefore, P = 6n + 2 – V = 6 * 6 + 2 – 34 = 4 There are 4π electrons in N2O4and that means 2 double bonds or a triple bond must be added to the structure in Step 1.
However, all the atoms present are second row elements and cannot accommodate more than 8 valence electrons. Therefore, a triple bond cannot be used as it would place ten electrons around the atoms bonded. The only possible case is that of two double bonds.
Step 3 & 4: The Lewis structure for N2O4 is as follows:
Figure 1: Lewis electron dot structures for N2O4 |
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