Lewis structure of CN-

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The Lewis structure of CN^– contains a triple bond between the carbon atom and nitrogen atom, and both the atoms have one lone pair.

Plus, there is a negative (-1) charge on the carbon atom.

Steps

By using the following steps, you can easily draw the Lewis structure of CN^–:

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Complete octet on central atom
#5 Calculate formal charge and check stability

Let’s one by one discuss each step in detail.

#1 Draw skeleton

In this step, first calculate the total number of valence electrons. And then, decide the central atom.

• Let’s calculate the total number of valence electrons

We know that… carbon is a group 14 element and nitrogen is a group 15 element. Hence, carbon has four valence electrons and nitrogen has five valence electrons.

Now CN^– has one carbon atom and one nitrogen atom.

So the total number of valence electrons = valence electrons of carbon atom + valence electrons of nitrogen atom

And CN^– has a negative (-1) charge, so we have to add one more electron.

Therefore, the total number of valence electrons = 4 + 5 + 1 = 10

• Now decide the central atom

The atom with the least electronegative value is placed at the center. By looking at the periodic table, we get the electronegativity values for carbon and nitrogen as follows:

Electronegativity value of carbon = 2.55
Electronegativity value of nitrogen = 3.04

Obviously, carbon is less electronegative than nitrogen. Hence, assume that carbon is the central atom.

So now, put carbon and nitrogen next to each other. And draw the rough skeleton structure for the Lewis structure of CN^– something like this:

Also read: How to draw Lewis structure of CF₄ (4 steps)

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond as follows:

#3 Mark lone pairs

As calculated earlier, we have a total of 10 valence electrons. And in the above structure, we have already used two valence electrons. Hence, eight valence electrons are remaining.

Two valence electrons represent one lone pair. So eight valence electrons = four lone pairs.

Note that both (carbon and nitrogen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell.

Also, make sure that you start marking these lone pairs on outside atoms first. And then, on the central atom.

The outside atom is nitrogen, so nitrogen will get three lone pairs. And the central atom (carbon) will get one lone pair.

So the Lewis structure of CN^– looks something like this:

In the above structure, you can see that the octet is completed on the outside atom. But, the central atom (carbon) doesn’t form an octet.

So in the next step, we have to complete the octet on the central atom.

Also read: How to draw Lewis structure of PF₃ (4 steps)

#4 Complete octet on central atom

Remember that carbon is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Now carbon already has four valence electrons. Hence, carbon needs four more valence electrons to complete its octet.

So convert two lone pairs from the nitrogen atom to make a new bond with the carbon atom. And then, the Lewis structure of CN^– looks something like this:

In the above structure, you can see that the octet is completed on the central atom (carbon), and also on the outside atom. Therefore, the octet rule is satisfied.

After completing the octet, one last thing we need to do is, calculate the formal charge and check the stability of the above structure.

Also read: How to draw Lewis structure of XeF₄ (4 steps)

#5 Calculate formal charge and check stability

The following formula is used to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

Collect the data from the above structure and then, write it down below as follows:

• For carbon atom

Valence electrons = 4
Nonbonding electrons = 2
Bonding electrons = 6

Formal charge = 4 – 2 – ½ (6) = -1

• For nitrogen atom

Valence electrons = 5
Nonbonding electrons = 2
Bonding electrons = 6

Formal charge = 5 – 2 – ½ (6) = 0

Mention the formal charges of atoms on the structure. So the Lewis structure of CN^– looks something like this:

In the above structure, you can see that the formal charges of atoms are closer to zero. Therefore, this is the most stable Lewis structure of CN^–.

And each horizontal line drawn in the above structure represents a pair of bonding valence electrons.

Now CN^– is an ion having a negative (-1) charge, so draw brackets around the above Lewis structure and mention that charge on the top right corner. And then, the Lewis structure of CN^– looks something like this:

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Related

• Lewis structure of CF₄
• Lewis structure of PF₃
• Lewis structure of XeF₄
• Lewis structure of F₂
• Lewis structure of PO₄^3-

External links

• Worked example: Lewis diagram of the cyanide ion (CN-) – Khan Academy
• CN- Lewis Structure in 6 Steps (With Images) – Pediabay
• Chemical Bonding: CN- Lewis Structure – The Geoexchange
• Draw the Lewis structure for CN- and determine the formal charge of each atom – Homework.Study.com
• What Is The Correct Lewis Structure For CN-? – Chegg
• Cyanide Ion (CN-) Formal Charge – Chemistry Learner
• Lewis Dot of the Cyanide Ion CN- – Kent’s Chemistry
• CN Lewis Structure, Molecular Geometry, Hybridization, Polarity, and MO Diagram – Techiescientist
• Lewis structure of CN radical – Chemistry Stack Exchange
• CN-(Cyanide ion) Lewis Structure, Molecular Geometry and Polarity – Geometry of Molecules
• CN- lewis structure, molecular orbital diagram, bond order, geometry – Topblogtenz
• Draw the Lewis structure with lowest formal charges, and determine the charge of each atom in CN- – Quizlet
• What is the charge on CN? – Quora