Ready to learn how to draw the lewis structure of OCN- ion (cyanate ion)?
Here, I have explained 6 simple steps to draw the lewis dot structure of OCN- 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 OCN- (or Cyanate ion) has a triple bond between the Carbon-Nitrogen atom and a single bond between Carbon-Oxygen atom. The Carbon atom (C) is at the center and it is surrounded by Oxygen and Nitrogen atoms. The Oxygen atom has 3 lone pairs and the Nitrogen atom has 1 lone pair, 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 OCN- ion).
6 Steps to Draw the Lewis Structure of OCN-
Step #1: Calculate the total number of valence electrons
Here, the given ion is OCN- (cyanate ion). In order to draw the lewis structure of OCN, first of all you have to find the total number of valence electrons present in the OCN- 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 OCN-
- For Oxygen:
Oxygen is a group 16 element on the periodic table. 
Hence, the valence electron present in oxygen is 6 (see below image).
- For Carbon:
Carbon is a group 14 element on the periodic table. 
Hence, the valence electrons present in carbon is 4 (see below image).
- For Nitrogen:
Nitrogen is a group 15 element on the periodic table. 
Hence, the valence electrons present in nitrogen is 5 (see below image).
Hence in a OCN- ion,
Valence electrons given by Oxygen (O) 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 OCN- 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). 
Here in the OCN molecule, if we compare the oxygen atom (O), carbon atom (C) and nitrogen atom (N), then the carbon is less electronegative.
So, carbon should be placed in the center and the remaining oxygen 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 OCN molecule, put the two electrons (i.e electron pair) between the oxygen atom, carbon atom and nitrogen atom to represent a chemical bond between them.
These pairs of electrons present between the Oxygen (O), Carbon (C) and Nitrogen (N) atoms form a chemical bond, which bonds these atoms with each other in a OCN 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 OCN, 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 OCN- 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 OCN.
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 to form a double bond.
Now the question is, from which atom should we move the electron pair?
From nitrogen? or
From oxygen? or
Well, we should move the electron from the atom which is less electronegative. Because the less electronegative atom has more tendency to lose the electrons.
Here, nitrogen is less electronegative than oxygen. Hence we should move electron pair from nitrogen.
Still, the octet of carbon atom is not fulfilled as it has only 6 electrons.
So again moving the electron pair from nitrogen atom only, 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 Oxygen atom (O), 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 Oxygen:
Valence electrons = 6 (as it is in group 16)
Nonbonding electrons = 6
Bonding electrons = 2
- 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 = 2
Bonding electrons = 6
|Formal charge||=||Valence electrons||–||Nonbonding electrons||–||(Bonding electrons)/2|
Lets keep these charges in the above lewis structure.
As you can see in the above sketch, there is one -ve charge on the oxygen atom, which indicates the -1 formal charge on the OCN molecule. Also the most electronegative atom (i.e oxygen) has the -ve charge.
Hence, the above lewis structure of OCN- ion is the stable lewis structure.
Each electron pair (:) in the lewis dot structure of OCN- ion represents the single bond ( | ). So the above lewis dot structure of OCN- ion can also be represented as shown below.
Related lewis structures for your practice:
Lewis structure of ICl4-
Lewis structure of SiF4
Lewis structure of CH3F
Lewis structure of NH4+
Lewis structure of NH2-