BF3): Lewis Structure, Molecular Geometry, Hybridization, And MOT Diagram

Boron Trifluoride (BF3) is an inorganic compound, it does not have a C-H bond and is a colourless gas.

This blog post covers the Lewis structure, molecular geometry, hybridization, and MOT of Boron Trifluoride (BF3). Moreover, let’s quickly go through some more details about boron trifluoride. Now let’s know more about this compound.

Facts About Boron Trifluoride (BF3)

Table of Contents

  • It occurs in a gas state at room temperature.
  • It is a colourless compound.
  • It is a toxic gas.
  • When mixed with air, it forms white fumes.

Valence Electrons

A valence electron is an electron present in an atom’s outermost shell or energy level. Valence electrons make bonds. They also determine the chemical properties of the particles.

Formal Charge

A formal charge is assigned to an atom in a molecule, supposing that all the bonding electrons were shared equally.

Draw Lewis Structure of Boron Trifluoride (BF3)

There are some general rules to draw a Lewis structure of a molecule. Here we will use those rules to draw the Lewis structure of BF3. If you are a beginner, take a pen and paper with you and draw these sections slowly and correctly with me.

Step 1: Find the Total no. of Valence Electrons in BF3

As you know, valence electrons are the no. of electrons present in the outermost shell of an atom.

For Boron

Boron is an element of group 13. Hence, the Boron has 3 valence electrons.

For Fluorine

Fluorine is an element of group 17. Hence, Fluorine has 7 valence electrons.

Hence in a BF3 molecule,

Valence electrons by Boron atom = 3

Valence electrons by each Fluorine atom = 7

Total no. of valence electrons in BF3 = 3 + 7(3) = 24

Step 2: Find the Center Atom in BF3

Always remember that the least electronegative element is located at the molecule’s centre. In Boron Trifluoride (BF3) , Boron is less electronegative than Fluorine. That’s why we will place Boron in the centre. Fluorine atoms will surround the centre atom.

Step 3: Place Electrons Between Atoms to Show a Chemical Bond

In the above sketch, place the electron pair between the boron and fluorine atoms. This makes a chemical bond between these atoms.

Step 4: Complete the Octet Rule on Outside Atoms

In the Lewis structure of BF3, the outer atoms are fluorine atoms. We have to complete the octet on these fluorine atoms. Each Fluorine requires eight electrons to have a complete valence shell.

Step 5: Check the Stability of Lewis Structure by Calculating the Formal Charge

In this step, you must check formal charges on Boron and fluorine atom. The formula for that is

The formal charge on the atom = Valence shell electrons – Non-bonding electrons – bonding electrons/2

Formal charge Valence electrons Nonbonding electrons Bonding electrons/2






6/6 = 0


Importance of Lewis Structure

  • A Lewis structure is a clear representation of valence electrons in a molecule.
  • It shows how the electrons are arranged around atoms in a molecule.
  • Lewis structure of a molecule allows you to know two things. First how the atoms bonded. Second, how many bonds it forms.
  • This knowledge helps us to know the shape and nature of the molecule.

Molecular Geometry and Shape of Boron Trifluoride (BF3)

The geometry of the BF3 molecule is trigonal planar. There is an even or symmetric charge distribution on the central atom. It is a non-polar molecule.

If we look closely at a BF3 molecule, we see that three fluorine atoms surround one boron atom. This confirms that its geometry is trigonal planar—the three fluorine atoms at the outer side of the boron form an equilateral triangle.

Determine Geometry of BF3 by AXN Notation

We can also determine the geometry of Boron Trifluoride (BF3) using the VSEPR theory. For this purpose, we use the AXN notation method.

A represents the central atom. In BF3, A is Boron.

A = Boron

X shows the atoms bonded to Boron. In Boron Trifluoride (BF3) , three F atoms are bonded to Boron. So,

X = 3

N represents the no. of lone pair of electrons. Boron has no lone pair of electrons. So,

N = 0

Now, the AXN formula for BF3 is AX3.

According to VSEPR, a molecule with the AX3 formula has trigonal planar geometry.

Bond Angle of Boron Trifluoride (BF3)

BF3 has such a geometry that three electron-rich regions lie symmetrically around the central atom. This makes an equilateral triangle. Due to this arrangement, the bond angle of the BF3 molecule is 120˚

Polarity of Boron Trifluoride (BF3)

The overall charge on a molecule shows the polarity of the molecule. If we see the molecule of Boron Trifluoride (BF3) , the overall charge is zero. Zero charge means that it is a non-polar molecule. This is due to the very less electronegativity difference in Boron and Fluorine atoms.

Factors Affecting the Polarity

  • Electronegativity difference of the bonded atoms

Since polarity means the pulling of electrons, hence a more electronegative element can attract more electrons. As a result, electrons move towards the more negative element.

  • Space arrangement of bonds in the atom

The shared electron pair also observes pulling force from other electron pairs. Hence, the same atoms have different polarities in different molecules.

Hybridization of Boron Trifluoride (BF3)

Hybridization is the combination of atomic orbitals to form new hybrid orbitals. Based on how orbitals are mixed, there are six types of hybridization.

The type of hybridization found in the Boron Trifluoride (BF3) molecule is sp2 In the molecule, all the bonds formed are sigma bonds. Three sp2 hybrid orbitals of Boron make bonds with three p orbitals of Fluorine.

MOT Diagram of Boron Trifluoride (BF3)

Drawing a molecular orbital diagram is perhaps the trickiest thing in chemistry. Let’s see how we can draw the MOT of this molecule.

  • First, we have to determine the point group- a group that describes all symmetry operations. ( if linear, use D2h or C2v)
  • Then allot XYZ axes
  • After that, we have to determine the unclear representation of outer atomic orbitals. (We have to follow common rules i.e., move = 0, no change = 1, sign change= -1)
  • Now we will determine a clear representation of outer atom orbitals (symmetry adapted linear combinations SALCs)
  • Let’s find central atom AOs having the exact symmetry
  • Finally, we draw the molecular orbital diagram. For this, we use central atom AOs and SALCs having similar energy and the same symmetry.

Physical and Chemical Properties of Boron Trifluoride (BF3)

  • Boron trifluoride is a colourless gas and has a pungent odour.
  • It is toxic.
  • It is soluble in water.
  • Its melting and boiling points are -127 ˚C and -100 ˚C, respectively.
  • It is an electron-deficient compound.
  • It is one of the most vital Lewis acid electron-pair acceptors).
  • Its molecular weight is 67.81.

Uses of Boron Trifluoride (BF3)

  • It works as a catalyst in polymerization reactions.
  • It is used in the production of adhesives.
  • It is used in lubricants.
  • It is used in fibre optics.
  • It is also helpful in fire extinguishing.


The highly symmetrical structure of BF3 results in a net-zero dipole moment. The non-polar nature of the molecule describes its properties which we have discussed above. After reading the article, you can understand the Lewis structure, geometry, and MOT diagram of BF3. If you have any questions regarding this topic, feel free to ask in the comment section.

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Q1: Can BF3 dissolve in water?

BF3 is soluble in water. It reacts with water to give boric acid and fluoroboric acid. It is incredibly soluble in the liquid state. It gets hydrolyzed by cold water. As a result, it provides a corrosive material, hydrofluoric acid.

Q2: Why is BF3 stable?

Boron has formed the maximum no. of bonds it can. Energy is emitted when a covalent bond is formed. This is the reason it is an exothermic process. Energy is lost after the formation of each bond. This shows that the structure of BF3 is perfectly valid.

Q3: Does BF3 obey the octet rule?

It does not obey the octet rule. In this molecule, Fluorine shares one electron from Boron and completes its octet. At the same time, Boron shares three Fluorine atoms and has 6 electrons in the outermost shell having an incomplete octet.

Q4: Is BF3 ionic or covalent?

BF3 is a covalent compound. As we know, a covalent compound is formed by sharing electrons between atoms. In the molecule, the atoms share their electrons. This bond is formed as a result of the high ionization energy of Boron.

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