Boron tribromide (BBr3) lewis dot structure, molecular geometry, polar or nonpolar, hybridization

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BBr3 lewis structure molecular geometry

Boron tribromide composed of boron and bromine appears as colorless to amber liquid, has a sharp and irritating odor with chemical formula BBr3.

In this tutorial, we will discuss BBr3 lewis structure, molecular geometry, polar or nonpolar, etc.

Bromide tribromide decomposes by water and alcohols, and it reacts violently with water. It is used in image processing, organic synthesis, photovoltaic manufacturing, etc.

Name of MoleculeBoron tribromide
Chemical formulaBBr3
Molecular geometry of BBr3Trigonal planar
Electron geometry of BBr3Trigonal planar
Total Valence electron for BBr324

How to draw lewis structure of BBr3?

BBr3 lewis structure contains three B-Br bonds with boron in a central position and all three bromine atoms in an outside position. The lewis structure of BBr3 contains a total of 3 bond pairs and 9 lone pairs.

The drawing of the BBr3 lewis’s structure is very easy and simple. Let’s see how to do it.

Follow some steps for drawing the Lewis dot structure for BBr3

1. Count total valence electron in BBr3

First of all, determine the valence electron that is available for drawing the lewis structure of BBr3 because the lewis diagram is all about the representation of valence electrons on atoms.

So, an easy way to find the valence electron of atoms in the BBr3 molecule is, just to look at the periodic group of boron and bromine atoms.

As the boron atom belongs to the 13th group in the periodic table and bromine is situated in the 17th group, hence, the valence electron for the boron is 3, and for the bromine atom, it is 7.

⇒ Total number of the valence electrons in boron = 3

⇒ Total number of the valence electrons in bromine = 7

∴ Total number of valence electron available for the BBr3 Lewis structure = 3 + 7×3 = 24 valence electrons         [∴BBr3 molecule has one boron and three bromine atoms]

Total number of valence electron available for the BBr3 Lewis structure

2. Find the least electronegative atom and place it at center

An atom with a less electronegative value is preferable for the central position in the lewis diagram because they are more prone to share the electrons with surrounding atoms.

In the case of the BBr3 molecule, the boron atom is less electronegative than the bromine atom.

Hence, put the boron atom at the central position of the lewis diagram and all three bromine atoms outside it.

central atom in bbr3

3. Connect outer atoms to the central atom with a single bond

In this step, join all outer atoms to the central atom with the help of a single bond.

In, the BBr3 molecule, bromine is the outer atom, and boron is the central atom. Hence, joined them. 

skeletal structure of BBr3

Count the number of valence electrons used in the above structure. There are 3 single bonds used in the above structure, and one single bond means 2 electrons.

Hence, in the above structure, (3 × 2) = 6 valence electrons are used from a total of 24 valence electrons available for drawing the BBr3 Lewis structure.

∴ (24 – 6) = 18 valence electrons

So, we are left with 18 valence electrons more.

4. Place remaining electrons on the outer atom first and complete their octet

Let’s start putting the remaining valence electrons on outer atoms first. In the case of the BBr3 molecule, bromine is the outer atom and each of them needs 8 electrons in its valence shell to complete the octet.

Start putting the remaining electrons on bromine atoms as dots till they complete their octet.

BBr3 Lewis dot structure

So, all bromine atoms in the above structure completed their octet, because all of them have 8 electrons(electrons represented as dots + 2 electrons in every single bond) in their outermost shell. 

Now again count the valence electron in the above structure.

In the above structure, there is 18 electrons are represented as dots + three single bonds that contain 6 electrons means a total of 24 valence electrons is used in the above structure.

So, we have used all the valence electrons available for drawing the lewis structure of BBr3.

5. Complete the octet of the central atom

We don’t have any extra valence electrons left and the central atom boron has only 6 electrons(3 single bonds) in its valence shell.

It should be noted that Boron is exceptional to the octet rule as it can have 8 electrons or less than 8 electrons in the outermost shell to attain stability. Boron is an exception just like aluminum where it can be octet deficient.

Octet deficient molecules are the molecules that can attains the stability by having less than 8 electrons around the atoms. Some examples – Boron, beryllium, aluminium, hydrogen, lithium, helium

But boron and aluminium is two most common element that can fail to complete the octet as they attains stability having only 6 valence electrons. 

Therefore, the boron central atom in the BBr3 lewis structure attains stability by just having 6 valence electrons around it.

Let’s check the formal charge for the 4th step structure to verify it’s stable or not.

6. Check the stability with the help of a formal charge concept

The lesser the formal charge on atoms, the better is the stability of the lewis diagram.

To calculate the formal charge on an atom. Use the formula given below-

⇒ Formal charge = (valence electrons – nonbonding electrons –  1/2 bonding electrons)

Let’s count the formal charge for the 4th step structure.

 For bromine atom

⇒ Valence electrons of bromine = 7

⇒ Nonbonding electrons on bromine = 6

⇒ Bonding electrons around bromine (1 single bond) = 2

∴ (7 – 6 – 2/2) = 0 formal charge on the bromine atom.

 For boron atom

⇒ Valence electrons of boron = 3

⇒ Nonbonding electrons on boron = 0

⇒ Bonding electrons around boron (3 single bonds) = 6

∴ (3 – 0 – 6/2) = 0 formal charge on the boron central atom.

BBr3 Lewis structure

BBr3 lewis structure

Hence, in the above BBr3 lewis structure, all atoms get a formal charge equal to zero. Even the boron central atom has only 6 electrons instead of 8 in the valence shell, it also gets a formal charge equal to zero.

We have no required to form multiple bonds and provide boron atom to 8 electrons in its valence shell.

The boron can achieve stability by just having 6 electrons in the valence shell.

Therefore, the above lewis structure of BBr3 is most stable and appropriate.

Also check – 

What is the molecular geometry of BBr3?

The molecular geometry of BBr3 is trigonal planar because the central atom boron is bonded with three bromine atoms and it contains no lone pair that means, it is an AX3 type molecule.

A represent central atom

X represent the number of bonded atom to central atom

According to VSEPR theory or chart, the AX3 type molecule forms trigonal planar molecular geometry.

BBr3 molecular geometry or shape

Hybridization of BBr3

The hybridization of BBr3 is Sp2 because the steric number of the boron central atoms is three.

The calculation of steric number is done by adding a number of bonded atoms attached to the central atom and lone pair on the central atom.

In the case of the BBr3 molecule, boron is the central atom that is attached to the three bonded atoms(bromine) and it has no lone pairs.

Hence, (3 + 0) = 3 is the steric number of central atom boron in the BBr3 molecule that gives Sp2 hybridization.

Steric numberHybridization

Is BBr3 polar or nonpolar?

So, Is BBr3 polar or nonpolar? Well, it is obvious that BBr3 is a nonpolar molecule because each B-Br bond is directed at the angle of 120° to each other in a plane, hence, canceling of dipole moment generated along these bonds is very easy.

Therefore, no dipole moment is generated in the BBr3 molecule, hence, it is nonpolar in nature.

Also, the molecular geometry of BBr3 is very symmetrical since no lone pair is present on the central atom that can cause distortion in a molecule, so, the charges are distributed uniformly all over the atoms.

Hence, the dipole generated in the BBr3 molecule will easily cancel out each other leaving this molecule nonpolar in nature.

Also check-


The total number of lone pairs present in the lewis structure of BBr3?

The lone pair are represented as dots in the lewis diagram. According to the BBr3 lewis structure, there is a total of 18 dots present(6 dots on each bromine atom).

Hence, the number of lone pairs in the BBr3 lewis structure is 9.

The total number of bond pairs present in the lewis structure of BBr3?

The bond pairs simply are the bonding electrons that are found between the atoms, generally in the covalent bond.

Two bonding electron between the atoms forms a single covalent bond.

Now, as per BBr3 lewis structure, the central atom boron is attached with three single covalent bonds, and one single covalent bond means 2 bonding electrons.

Hence, total bonding electrons is (3 × 2) = 6 bonding electrons that make 3 bond pairs.

Also Read:

Properties of Boron tribromide

  • It is colorless and has an irritating odor.
  • It reacts violently with water and other protic solvents.
  • It is a strong lewis acid.
  • It is soluble in CH2Cl2, CCl4.
  • It has a boiling point of 91.3 °C and a melting point of −46.3 °C.

Preparation of Boron tribromide

Boron tribromide is prepared by reacting boron trioxide with 3 moles of carbon and 3 moles of bromine at high temperatures.

⇒ B2O3 + 3C + 3Br2 →  2BBr3 + 3CO


  • The total valence electron is available for drawing the BBr3 Lewis structure is 24.
  • The molecular geometry or shape of BBr3 is trigonal planar.
  • BBr3 is nonpolar and has Sp2 hybridization.
  • In the BBr3 Lewis structure, a total of 18 nonbonding electrons and 6 bonded electrons are present.
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