Rules for writing Lewis electron resonance structures– Formamidine

A simple and automatic method for writing Lewis Dot Structures is 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 consider the case of the Lewis Dot Structures of formamidine HNCHNH₂

Step 1:  Connect the atoms with single bonds:

 

 

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

Where n in this case is 3 since formamidine has 3 non-hydrogen atoms.

Where V = 1*1 + 1*5 + 1*4 + 1*1 +1*5 +1*1 +1*1 = 18, V is the number of valence electrons of the atom.

Therefore, P = 6n + 2 – V = 6 *3 + 2 – 18 = 2   there is 1 double bond.

The Lewis electron resonance structures of  formamidine  are as follows:

Structure #1 is the most stable electron dot structure because there is an octet of electrons around each atom and there is no charge separation.

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Relevant Posts

Lewis Structures and the Octet Rule - A simple method to write Lewis Structures

Simple Method for writing the Lewis Structures of carbon disulfide CS₂

 

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References

1. G.N. Lewis, J.A.C.S, 38, 762-785, (1916)
2. E. C. McGoran, J. Chem. Educ., 68, 19-23 (1991)
3. A.B.P. Lever, J. Chem. Educ., 49, 819-821, (1972)

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