Lewis structure of BrCN

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The Lewis structure of BrCN contains one single bond and one triple bond, with carbon in the center, and bromine and nitrogen on either side. The bromine atom has three lone pairs, the nitrogen atom has one lone pair, and the carbon atom does not have any lone pair.

Steps

By using the following steps, you can easily draw the Lewis structure of BrCN.

#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… bromine is a group 17 element, carbon is a group 14 element, and nitrogen is a group 15 element. Hence, bromine has seven valence electrons, carbon has four valence electrons, and nitrogen has five valence electrons.

Now BrCN has one bromine atom, one carbon atom, and one nitrogen atom.

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

Therefore, the total number of valence electrons = 7 + 4 + 5 = 16

• 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 bromine, carbon, and nitrogen as follows:

Electronegativity value of bromine = 2.96
Electronegativity value of carbon = 2.55
Electronegativity value of nitrogen = 3.04

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

So now, put carbon in the center and bromine and nitrogen on either side. And draw the rough skeleton structure for the Lewis structure of BrCN something like this:

Also read: How to draw Lewis structure of AsCl₃ (4 steps)

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since carbon is surrounded by bromine and nitrogen, use six electrons to show three chemical bonds as follows:

#3 Mark lone pairs

As calculated earlier, we have a total of 16 valence electrons. And in the above structure, we have already used six valence electrons. Hence, twelve valence electrons are remaining.

Two valence electrons represent one lone pair. So twelve valence electrons = six lone pairs.

Note that bromine is a period 4 element, so it can keep more than 8 electrons in its last shell. And 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 atoms are bromine and nitrogen, so bromine and nitrogen will get three lone pairs. And the central atom (carbon) will not get any lone pair, because all six lone pairs are used.

So the Lewis structure of BrCN looks something like this:

In the above structure, you can see that the octet is completed on outside atoms. 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 XeH₄ (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 BrCN looks something like this:

Here, the lone pair of nitrogen is converted (instead of bromine). But bromine is less electronegative than nitrogen, so why not the lone pair of bromine is converted?

This is because… we do not get the formal charges on atoms closer to zero, if we convert the lone pair of bromine.

In the above structure, you can see that the octet is completed on the central atom (carbon), and also on the outside atoms. 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 BeI₂ (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 bromine atom

Valence electrons = 7
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 7 – 6 – ½ (2) = 0

• For carbon atom

Valence electrons = 4
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 4 – 0 – ½ (8) = 0

• 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 BrCN looks something like this:

In the above structure, you can see that the formal charges of all atoms are zero. Therefore, this is the stable Lewis structure of BrCN.

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

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Related

• Lewis structure of AsCl₃
• Lewis structure of XeH₄
• Lewis structure of BeI₂
• Lewis structure of SiCl₂Br₂
• Lewis structure of POCl₃

External links

• BrCN Lewis Structure in 6 Steps (With Images) – Pediabay
• BrCN Lewis Structure, Geometry, Hybridization, Polarity – Techiescientist
• Draw the Lewis structure for BrCN – Chegg
• Draw the Lewis structure for BrCN? – OneClass
• BrCN (Cyanogen Bromide) Oxidation Number – ChemicalAid