Lewis Structure of SCN- (With 6 Simple Steps to Draw!)

Ready to learn how to draw the lewis structure of SCN- ion?

Awesome!

Here, I have explained 6 simple steps to draw the lewis dot structure of SCN- ion (along with images).

So, if you are ready to go with these 6 simple steps, then let’s dive right into it!

Lewis structure of SCN- (or Thiocyanate ion) contains two double bonds between the Carbon-Sulfur atoms and Carbon-Nitrogen atoms. The Carbon atom (C) is at the center and it is surrounded by Sulfur and Nitrogen atoms. The Sulfur atom and Nitrogen atom have 2 lone pairs, while the carbon atom does not have lone pairs.

Let’s draw and understand this lewis dot structure step by step.

(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of SCN- ion).

6 Steps to Draw the Lewis Structure of SCN-

Step #1: Calculate the total number of valence electrons

Here, the given ion is SCN- (thiocyanate ion). In order to draw the lewis structure of SCN, first of all you have to find the total number of valence electrons present in the SCN- ion.
(Valence electrons are the number of electrons present in the outermost shell of an atom).

So, let’s calculate this first.

Calculation of valence electrons in SCN-

• For Sulfur:

Sulfur is a group 16 element on the periodic table. ^[1]

Hence, the valence electrons present in sulfur is 6 (see below image).

• For Carbon:

Carbon is a group 14 element on the periodic table. ^[2]

Hence, the valence electrons present in carbon is 4 (see below image).

• For Nitrogen:

Nitrogen is a group 15 element on the periodic table. ^[3]

Hence, the valence electrons present in nitrogen is 5 (see below image).

Hence in a SCN- ion, 

Valence electrons given by Sulfur (S) atom = 6
Valence electrons given by Carbon (C) atom = 4
Valence electrons given by Nitrogen (N) atom = 5
Electron due to -1 charge, 1 more electron is added
So, total number of Valence electrons in SCN- ion = 6 + 4 + 5 + 1 = 16

Step #2: Select the center atom

While selecting the atom, always put the least electronegative atom at the center. 

(Remember: Fluorine is the most electronegative element on the periodic table and the electronegativity decreases as we move right to left in the periodic table as well as top to bottom in the periodic table). ^[4]

Here in the SCN molecule, if we compare the sulfur atom (S), carbon atom (C) and nitrogen atom (N), then the carbon is less electronegative.

So, carbon should be placed in the center and the remaining sulfur and nitrogen atom will surround it.

Step #3: Put two electrons between the atoms to represent a chemical bond

Now in the above sketch of SCN molecule, put the two electrons (i.e electron pair) between the sulfur atom, carbon atom and nitrogen atom to represent a chemical bond between them.

These pairs of electrons present between the Sulfur (S), Carbon (C) and Nitrogen (N) atoms form a chemical bond, which bonds these atoms with each other in a SCN molecule.

Step #4: Complete the octet (or duplet) on outside atoms. If the valence electrons are left, then put the valence electrons pair on the central atom

Don’t worry, I’ll explain!

In the Lewis structure of SCN, the outer atoms are oxygen atom and nitrogen atom.

So now, you have to complete the octet on these outer atoms.

Now, you can see in the above image that both the oxygen atom as well as nitrogen atom form an octet.

Also, all the 16 valence electrons of SCN- ion (as calculated in step #1) are used in the above structure. So there are no remaining electron pairs.

Hence there is no change in the above sketch of SCN.

Let’s move to the next step.

Step #5: Check whether the central atom has octet or not. If it does not have an octet, then move the electron pair from the outer atom to form a double bond or triple bond

In this step, we have to check whether the central atom (i.e carbon) has an octet or not. 

In simple words, we have to check whether the central carbon (C) atom has 8 electrons or not.

As you can see from the above image, the central atom (i.e carbon) has only 4 electrons. So it does not fulfill the octet rule.

Now, in order to fulfill the octet of carbon atom, we have to move the electron pair from the outer atom (i.e sulfur atom) to form a double bond.

Still, the octet of carbon atom is not fulfilled as it has only 6 electrons.

So again moving the electron pair from nitrogen atom, we will get the following structure.

Now you can see from the above image that the central atom (i.e carbon), is having 8 electrons. So it fulfills the octet rule.

Step #6: Final step – Check the stability of lewis structure by calculating the formal charge on each atom

Now, you have come to the final step and here you have to check the formal charge on Sulfur atom (S), Carbon atom (C) as well as Nitrogen atom (N).

For that, you need to remember the formula of formal charge;

Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2

• For Sulfur:
  Valence electrons = 6 (as it is in group 16)
  Nonbonding electrons = 4
  Bonding electrons = 4
• For Carbon:
  Valence electron = 4 (as it is in group 14)
  Nonbonding electrons = 0
  Bonding electrons = 8
• For Nitrogen:
  Valence electron = 5 (as it is in group 15)
  Nonbonding electrons = 4
  Bonding electrons = 4

Formal charge	=	Valence electrons	–	Nonbonding electrons	–	(Bonding electrons)/2
S	=	6	–	4	–	4/2	=	0
C	=	4	–	0	–	8/2	=	0
N	=	5	–	4	–	4/2	=	-1

As you can see in the above sketch, there is one -ve charge on the nitrogen atom, which indicates the -1 formal charge on the SCN molecule. Also the most electronegative atom (i.e nitrogen) has the -ve charge.

Hence, the above lewis structure of SCN- ion is the stable lewis structure.

Each electron pair (:) in the lewis dot structure of SCN- ion represents the single bond ( | ). So the above lewis dot structure of SCN- ion can also be represented as shown below.

Related lewis structures for your practice:
Lewis structure of ClF3
Lewis structure of Cl2
Lewis structure of HF
Lewis structure of SCl2
Lewis structure of PF5

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