Valence Electrons and Lewis Dot Structures – HNCS

Valence Electrons and Lewis Dot Structures – Isothiocyanic acid (HNCS)

A simple method for writing Lewis Dot 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 now the case of  isothiocyanic acid  (HNCS). How can we write a draw of the Lewis structures?         

 

Step 1: Connect the atoms with single bonds.

 

Fig.1: Connect the atoms of isothiocyanic acid (HNCS) 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 isothiocyanic acid has one hydrogen atom.

Where V = 1*1 + 1*5 + 1*4 + 1*6 = 16, V is the number of valence electrons of the atom.

Therefore, P = 6n + 2 – V = 6 *3 + 2 – 16 = 4   Therefore,  there are 2 double bonds or a triple bond.

 

Step 3 & 4: The Lewis resonance structures of  HNCS  are as follows:

 Fig.2 : Electron dot structures of isothiocyanic acid (HNCS)

Structure #3 is the most stable resonance Lewis structure since there is an octet of electrons around each atom and there is no charge separation. Structure #1 is more stable than Structure #2 since the negative charge is on N (3.04) which is more electronegative than S (2.58)

---

Relevant Posts

Lewis Structure of Thiocyanate (SCN-)

Canonical Structures - Lewis Dot Structure of OCN-

Simple Procedure for writing the Lewis structures of CN+

---

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)

---

Key Terms

lewis structures, simple method for writing Lewis structures, valence electrons, single bonds, electrons in π bonds, resonance structures

---