Br3- Lewis structure

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.

Alternative method: Lewis structure of Br₃^–

Rough sketch

• 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

Lone pair

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:

Formal charge

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:

Final structure

The final structure of Br₃^– consists of a central bromine atom connected to two terminal bromine atoms through single covalent bonds. In this layout, the central bromine atom serves as an exception to the octet rule, utilizing an expanded valence shell to accommodate ten electrons through two bonding pairs and three lone pairs. Each terminal bromine atom satisfies its octet by retaining three lone pairs alongside its single shared bond with the central atom. This arrangement is the most stable because it places the -1 formal charge on the central bromine atom, while the terminal atoms maintain a formal charge of zero. Consequently, this specific electronic distribution serves as the definitive and most accurate Lewis representation of the tribromide ion.

To complete the representation, draw square brackets around the entire Lewis structure and place a “-” or “-1” sign as a superscript outside the upper right bracket. This notation signifies that the negative charge is a property of the whole ion.

Next: Br₂ Lewis structure

External video

• Br3- Lewis Structure: How to Draw the Lewis Structure for the Br3- – YouTube • Wayne Breslyn

External links

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