Br3- Lewis structure

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Br₃^– (tribromide) has three bromine atoms.

In the Br₃^– Lewis structure, there are two single bonds around the bromine atom, with two other bromine atoms attached to it, and on each bromine atom, there are three lone pairs.

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

Steps

To properly draw the Br₃^– Lewis structure, follow these steps:

#1 Draw a rough sketch of the structure
#2 Next, indicate lone pairs on the atoms
#3 Indicate formal charges on the atoms, if necessary

Let’s break down each step in more detail.

#1 Draw a rough sketch of the structure

• First, determine the total number of valence electrons

In the periodic table, bromine lies in group 17. Hence, bromine has seven valence electrons.

Since Br₃^– has three bromine atoms, so…

Valence electrons of three bromine atoms = 7 × 3 = 21

Now the Br₃^– has a negative (-1) charge, so we have to add one more electron.

So the total valence electrons = 21 + 1 = 22

Learn how to find: Bromine valence electrons

• Second, find the total electron pairs

We have a total of 22 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 = 22 ÷ 2 = 11

• Third, determine the central atom

Here, there are three atoms and all atoms are bromine, so we can assume any one as the central atom.

Let’s assume that the central atom is center bromine.

• And finally, draw the rough sketch

#2 Next, indicate lone pairs on the atoms

Here, we have a total of 11 electron pairs. And two Br — Br bonds are already marked. So we have to only mark the remaining nine electron pairs as lone pairs on the sketch.

Also remember that bromine is a period 4 element, so it can keep more than 8 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are left bromine and right bromine.

So for each bromine, there are three lone pairs.

Mark the lone pairs on the sketch as follows:

#3 Indicate formal charges on the atoms, if necessary

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

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

For left bromine and right bromine atom, formal charge = 7 – 6 – ½ (2) = 0

For center bromine atom, formal charge = 7 – 6 – ½ (4) = -1

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

In the above structure, you can see that the central atom (center bromine) forms an octet. And the outside atoms (left bromine and right bromine) also form an octet. Hence, the octet rule is satisfied.

Now there is still a negative (-1) charge on the center bromine atom.

This is okay, because the structure with a negative charge on the most electronegative atom is the best Lewis structure. And in this case, the most electronegative element is bromine.

Therefore, this structure is the most stable Lewis structure of Br₃^–.

And since the Br₃^– has a negative (-1) charge, mention that charge on the Lewis structure by drawing brackets as follows:

Next: Br₂ Lewis structure

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External links

• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/Br3–lewis-structure.html
• https://lambdageeks.com/br3-lewis-structure/