SCN- Lewis Structure in 6 Steps (With Images)

So you have seen the above image by now, right?

Let me explain the above image in short.

SCN- lewis structure has a Carbon atom (C) at the center which is surrounded by Sulfur atom (S) and Nitrogen atom (N). There are 2 double bonds between the Carbon (C) & Sulfur (S) atom as well as between Carbon (C) & Nitrogen (N) atom. There is a -1 formal charge on the Nitrogen atom (N).

If you haven’t understood anything from the above image of SCN- ion (thiocyanate ion) lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of SCN- ion.

So let’s move to the steps of drawing the lewis structure of SCN- ion.

Steps of drawing SCN- lewis structure

Step 1: Find the total valence electrons in SCN- molecule

In order to find the total valence electrons in SCN- (thiocyanate ion) ion, first of all you should know the valence electrons present in sulfur atom, carbon atom as well as nitrogen atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)

Here, I’ll tell you how you can easily find the valence electrons of sulfur, carbon as well as nitrogen using a periodic table.

Total valence electrons in SCN- ion

→ Valence electrons given by sulfur atom:

Sulfur is a group 16 element on the periodic table. ^[1] Hence the valence electrons present in sulfur is 6.

You can see the 6 valence electrons present in the sulfur atom as shown in the above image.

→ Valence electrons given by carbon atom:

Carbon is group 14 element on the periodic table. ^[2] Hence the valence electrons present in carbon is 4.

You can see the 4 valence electrons present in the carbon atom as shown in the above image.

→ Valence electrons given by nitrogen atom:

Nitrogen is a group 15 element on the periodic table. ^[3] Hence the valence electrons present in nitrogen is 5.

You can see the 5 valence electrons present in the nitrogen atom as shown in the above image.

Hence, 

Total valence electrons in SCN- ion = valence electrons given by 1 sulfur atom + valence electrons given by 1 carbon atom + valence electrons given by 1 nitrogen atom + 1 more electron is added due to 1 negative charge = 6 + 4 + 5 + 1 = 16.

Step 2: Select the central atom

For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.

Now here the given molecule is SCN and it contains sulfur atom (S), carbon atom (C) and nitrogen atom (N).

You can see the electronegativity values of sulfur atom (S), carbon atom (C) and nitrogen atom (N) in the above periodic table.

If we compare the electronegativity values of sulfur atom (S), carbon atom (C) and nitrogen atom (N) then the carbon atom is less electronegative.

So here the carbon atom (C) is the center atom and the sulfur atom (S) and nitrogen atom (N) are the outside atoms.

Step 3: Connect each atoms by putting an electron pair between them

Now in the SCN molecule, you have to put the electron pairs between the sulfur atom (S), carbon atom (C) and nitrogen atom (N).

This indicates that the sulfur atom (S), carbon atom (C) and nitrogen atom (N) are chemically bonded with each other in a SCN molecule.

Step 4: Make the outer atoms stable

Now in this step, you have to check the stability of the outer atoms.

Here in the sketch of SCN molecule, you can see that the outer atoms are sulfur atom and nitrogen atom.

These outer sulfur and nitrogen atoms are forming an octet and hence they are stable.

Also, in step 1 we have calculated the total number of valence electrons present in the SCN- ion.

The SCN- ion has a total 16 valence electrons and all these valence electrons are used in the above sketch.

Hence there are no remaining electron pairs to be kept on the central atom.

So now let’s proceed to the next step.

Step 5: Check the octet on the central atom. If it does not have octet, then shift the lone pair to form a double bond or triple bond.

In this step, you have to check whether the central carbon atom (C) is stable or not.

In order to check the stability of the central carbon (C) atom, we have to check whether it is forming an octet or not.

Unfortunately, the carbon atom is not forming an octet here. Carbon has only 4 electrons and it is unstable.

Now to make this carbon atom stable, you have to shift the electron pair from the outer sulfur atom so that the carbon atom can have 8 electrons (i.e octet).

But after shifting one electron pair, the carbon atom is still not forming an octet as it has only 6 electrons.

So again we have to shift one more electron pair from the nitrogen atom.

After shifting this electron pair, the central carbon atom will get 2 more electrons and thus its total electrons will become 8.

You can see from the above picture that the carbon atom is forming an octet.

And hence the carbon atom is stable.

Now let’s proceed to the final step to check whether the lewis structure of SCN is stable or not.

Step 6: Check the stability of lewis structure

Now you have come to the final step in which you have to check the stability of lewis structure of SCN molecule.

The stability of lewis structure can be checked by using a concept of formal charge.

In short, now you have to find the formal charge on sulfur (S), carbon (C) atom as well as nitrogen (N) atoms present in the SCN molecule.

For calculating the formal charge, you have to use the following formula;

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

You can see the number of bonding electrons and nonbonding electrons for each atom of SCN molecule in the image given below.

For Sulfur (S) atom:
Valence electrons = 6 (because sulfur is in group 16)
Bonding electrons = 4
Nonbonding electrons = 4

For Carbon (C) atom:
Valence electrons = 4 (because carbon is in group 14)
Bonding electrons = 8
Nonbonding electrons = 0

For Nitrogen (N) atom:
Valence electrons = 5 (because nitrogen is in group 15)
Bonding electrons = 4
Nonbonding electrons = 4

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

From the above calculations of formal charge, you can see that the nitrogen (N) atom has -1 charge, while other atoms have 0 charges.

So let’s keep these charges on the respective atoms in the SCN molecule.

This overall -1 charge on the SCN molecule is represented in the image given below.

In the above lewis dot structure of SCN- ion, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of SCN- ion.

I hope you have completely understood all the above steps.

For more practice and better understanding, you can try other lewis structures listed below.

Try (or at least See) these lewis structures for better understanding:

Cl2 lewis structure	HF lewis structure
SCl2 lewis structure	PF5 lewis structure
H2SO4 lewis structure	Ethanol (C2H5OH) lewis structure