So you have seen the above image by now, right?
Let me explain the above image in short.
CN- (cyanide ion) lewis structure has one Carbon atom (C) and one Nitrogen atom (N) which contain a triple bond between them. There is 1 lone pair on both the Carbon atom (C) as well as Nitrogen atom (N). There is a -1 formal charge on the Carbon atom (C).
If you haven’t understood anything from the above image of CN- (cyanide ion) lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of CN- ion.
So let’s move to the steps of drawing the lewis structure of CN- ion.
Steps of drawing CN- lewis structure
Step 1: Find the total valence electrons in CN- ion
In order to find the total valence electrons in a CN- (cyanide ion), first of all you should know the valence electrons present in a single 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 carbon as well as nitrogen using a periodic table.
Total valence electrons in CN- ion
→ Valence electrons given by carbon atom:
You can see the 4 valence electrons present in the carbon atom as shown in the above image.
→ Valence electrons given by nitrogen atom:
You can see the 5 valence electrons present in the nitrogen atom as shown in the above image.
Total valence electrons in CN- ion = valence electrons given by 1 carbon atom + valence electrons given by 1 nitrogen atom + 1 more electron is added due to 1 negative charge = 4 + 5 + 1 = 10.
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 ion is CN- ion. It has only two atoms, so you can select any of the atoms as a center atom.
Let’s assume the carbon atom as a central atom.
(You should assume the less electronegative atom as a center atom).
Step 3: Connect each atoms by putting an electron pair between them
Now in the CN molecule, you have to put the electron pairs between the carbon atom (C) and nitrogen atom (N).
This indicates that the carbon (C) atom and nitrogen (N) atom are chemically bonded with each other in a CN molecule.
Step 4: Make the outer atoms stable. Place the remaining valence electrons pair on the central atom.
Now in this step, you have to check the stability of the outer atom.
Here in the sketch of CN molecule, we have assumed the carbon atom as a center atom. So the nitrogen is the outer atom.
Hence you have to make the nitrogen atom stable.
You can see in the below image that the nitrogen atom is forming an octet and hence it is stable.
Also, in step 1 we have calculated the total number of valence electrons present in the CN- ion.
The CN- ion has a total 10 valence electrons and out of these, only 8 valence electrons are used in the above sketch.
So the number of electrons which are left = 10 – 8 = 2.
You have to put these 2 electrons on the carbon atom in the above sketch of CN molecule.
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 this carbon (C) atom, we have to check whether it is forming an octet or not.
Unfortunately, this 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 nitrogen atom.
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 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 as it has 8 electrons.
Now let’s proceed to the final step to check whether the above lewis structure 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 CN.
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 the carbon atom (C) as well as nitrogen atom (N) present in the CN molecule.
For calculating the formal charge, you have to use the following formula;
Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons
For Carbon (C) atom:
Valence electrons = 4 (because carbon is in group 14)
Bonding electrons = 6
Nonbonding electrons = 2
For Nitrogen (N) atom:
Valence electrons = 5 (because nitrogen is in group 15)
Bonding electrons = 6
Nonbonding electrons = 2
From the above calculations of formal charge, you can see that the carbon (C) atom has -1 charge and the nitrogen (N) atom has 0 charge.
So let’s keep these charges on the respective atoms in the CN molecule.
This overall -1 charge on the CN molecule is represented in the image given below.
In the above lewis dot structure of CN- ion, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of CN- 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:
|PF3 lewis structure
|PCl5 lewis structure
|H2O2 lewis structure
|F2 lewis structure
|CH2Cl2 lewis structure
|ClO2- lewis structure
Jay is an educator and has helped more than 100,000 students in their studies by providing simple and easy explanations on different science-related topics. He is a founder of Pediabay and is passionate about helping students through his easily digestible explanations.
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