CN- Lewis Structure

CN- Lewis Structure

CN (cyanide) has one carbon atom and one nitrogen atom. In the lewis structure of CN, there is a triple bond between the carbon and nitrogen atom, and on both carbon and nitrogen atoms, there is one lone pair.

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

Steps

Here’s how you can draw the CN lewis structure step by step.

Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: convert lone pair and mark charges again (if central atom doesn’t form octet)

Let’s break down each step in detail.

#1 Draw Sketch

  • First, determine the total number of valence electrons

In the periodic table, carbon lies in group 14, and nitrogen lies in group 15.

Hence, carbon has four valence electrons and nitrogen has five valence electrons.

Since CN has one carbon atom and one nitrogen atom, so…

Valence electrons of one carbon atom = 4 × 1 = 4
Valence electrons of one nitrogen atom = 5 × 1 = 5

Now the CN has a negative (-1) charge, so we have to add one more electron.

So the total valence electrons = 4 + 5 + 1 = 10

  • Second, find the total electron pairs

We have a total of 10 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 10 ÷ 2 = 5

  • Third, determine the central atom

We have to place the least electronegative atom at the center.

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

  • And finally, draw the rough sketch
CN- Lewis Structure (Step 1)

#2 Mark Lone Pairs

Here, we have a total of 5 electron pairs. And one C — N bond is already marked. So we have to only mark the remaining four electron pairs as lone pairs on the sketch.

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

Always start to mark the lone pairs from outside atoms. Here, the outside atom is nitrogen.

So for nitrogen, there are three lone pairs, and for carbon, there is one lone pair.

Mark the lone pairs on the sketch as follows:

CN- Lewis Structure (Step 2)

#3 Mark Charges

Use the following formula to calculate the formal charges on atoms:

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

For carbon atom, formal charge = 4 – 2 – ½ (2) = +1

For nitrogen atom, formal charge = 5 – 6 – ½ (2) = -2

Here, both carbon and nitrogen atoms have charges, so mark them on the sketch as follows:

CN- Lewis Structure (Step 3)

The above structure is not a stable lewis structure because both carbon and nitrogen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

#4 Minimize Charges

Convert a lone pair of the nitrogen atom to make a new C — N bond with the carbon atom as follows:

CN- Lewis Structure (Step 4)

In the above structure, you can see that the central atom (carbon) doesn’t form an octet. Hence, the octet rule is not satisfied.

#5 Convert Lone Pair and Mark Charges Again

Therefore, again convert a lone pair of the nitrogen atom to make a new C — N bond with the carbon atom. Also, we have to again check whether there are charges on atoms or not.

Use the following formula to calculate the formal charges on atoms:

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

For carbon atom, formal charge = 4 – 2 – ½ (6) = -1

For nitrogen atom, formal charge = 5 – 2 – ½ (6) = 0

Here, the carbon atom has a charge, so mark it on the sketch as follows:

CN- Lewis Structure (Step 5)

In the above structure, you can see that the central atom (carbon) forms an octet. Hence, the octet rule is satisfied.

Now there is still a negative (-1) charge on the carbon atom. But we can not convert a lone pair to a bond because carbon can not keep more than 8 electrons in its last shell.

The formal charges on atoms are closer to zero. Also, the above structure is more stable than the previous structures. Therefore, this structure is the most stable lewis structure of CN.

And since the CN has a negative (-1) charge, mention that charge on the lewis structure by drawing brackets as follows:

CN- Lewis Structure (Final)

Next: PF3 Lewis Structure

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