Best Overview on: BF3 Polar or Nonpolar [#1] - Science Education and Tutorials

Boron (B) is very peculiar chemical element in the periodic table. Boron trifluoride(BF3) is inorganic chemistry. Students of chemistry used to ask “Is BF3 polar or nonpolar?”. Because BF3 contains a central boron element and a high electronegativity value of fluorine atom. Three B-F bonds of BF3 molecule are polarized along with the covalent bond.

Boron Trifluoride (BF3) molecule, is an inorganic chemical compound that is a colorless gas in appearance with a pungent odour in smell. Owing to the existence of three Fluorine atoms with a very high electronegativity value as compared to the Boron atom, students often get confused about the polarity or non-polarity of B-F chemical bond in BF3 (Boron Trifluoride) molecule. In this blog post, we try to discuss the same in the detailed manner.

Is BF3 polar or non-polar? Because of its highly symmetric form, BF3 (Boron Trifluoride) is Non-Polar. It has a Trigonal Planar geometry that cancels out the dipole moments of the three B-F bonds, resulting in a compound with a Dipole Moment of 0 value (Zero). Now we will analyze various factors which are responsible for polarity or nonpolarity of the BF3 molecule.

Table of Contents

Is BF3 polar or nonpolar: Various factors

You’ve also learned of the chemical compound that doesn’t have any Carbon(C) and Hydrogen(H) atoms and covalent bonds. These types of compounds are referred to as “inorganic compounds” because they lack carbon atoms and therefore are not organic. The inorganic compound is boron trifluoride, which has the formula BF3.

It is a colorless, poisonous gas that has no color in normal atmospheric conditions. In moist air, it emits white gases due to its interaction with water(H2O) molecules. If the reaction goes to a high extreme, then it is in the form of a colorless liquid. BF3 molecule form weak coordination with two water molecules. It is BF3 coordination with dihydrate molecule.

BF3 Molecular Geometry

Any chemical compound, its molecular geometry plays a very important role to understand the physical and chemical properties of the molecule. The molecular geometry of molecule forms depends on the nature of atom in the molecule. The geometry of the molecule varies with the atom present in the molecule.

BF3 molecule has a ‘Trigonal Planar’ geometry. A model of three atoms around one boron atom in the center is known as a ‘Trigonal Planar’ in chemistry. It’s as if they’re all three peripheral fluorine atoms in one plane since the 120° bond angles on each of them make them an equilateral triangle nature.

The molecule BF3 (Boron Trifluoride) contains one atom of Boron (B , atomic number 5) in the center of trigonal geometry and three atoms of Fluorine (F , atomic no: 9) in the corner of trigonal plane. Since Boron (B) has an outermost valence electron of 3 and Fluorine (F) has an outermost valence electron of 7.

Each Fluorine (F) atom has three lone pairs of electrons, resulting in a balanced and symmetric molecular structure of BF3 molecule. The Boron Trifluoride(BF3) molecule has a Trigonal planar geometry, with each F-B-F bond angle equal to 120 degrees, according to the VSEPR (Valence Shell Electron Pair Repulsion) Theory, the Lewis structure of BF3 can be drawn as shown in the figure:

BF3 Lewis Structure

To draw a Lewis Structure of BF3 molecule, start by adding electrons and connecting them. In BF3 molecule, boron is having valence electron of three and three fluorine atom has seven valence electron. If we add this one boron and three fluorine atoms of the BF3 molecule, there are 24 electrons here in the BF3 molecular system.

Then, for the outer atom, add the octet rule and extra electrons, and for the central boron atom, add octets and extra electrons of the fluorine atom. But boron has two electron defficient. However, there are no extra electrons, as we all know. (0ctet rule electron = 24 – 24)

The central boron atom and three fluorine atoms of BF3 have 24 valence electrons, which we must arrange around it. Since it is the least electronegative element, boron will be at the center of the structure in BF3 molecule. Its outer shell requires six valence electrons. Boron is not following the octet rule law. Even though Boron only had six valence electrons, we can see that the formal charges for the Boron Trifluoride Lewis structure are zero as said above.

Electronegativity and chemical Bond Polarity of BF3

There are three B-F bonds in the BF3 (Boron Trifluoride) molecule, as seen in the Lewis diagram above. But all three B-F bond of BF3 molecule are polarise in nature. Its due to high electronegativity value of fluorine atom. It makes “Is BF3 polar or nonpolar ?”.

According to the Pauling scale,Boron(B) has an electronegativity of 2.04 and Fluorine(F) has an electronegativity value of 3.98 (maximum), implying that F (Fluorine) will draw the mutual electrons towards itself and thus gain a partial negative charge (-) and B (Boron) will have a partial positive charge (+).

Boron Electronegativity value = 2.04

Fluorine Electronegativity value = 3.98

Difference in electronegativity of B and F = 3.98 – 2.04 = 1.94

The difference between the electronegative value is greater than 0.5. The discrepancy between the electronegativity values of the boron and fluorine atoms in BF3 molecule sharing a covalent bond is used to decide whether a chemical bond is polar or nonpolar.

The difference between B’s and F’s electronegativity values is 1.94 (3.98 – 2.04 = 1.94), which is greater than 0.5. As a result, each three B-F bond in a molecule of BF3 (Boron Trifluoride) is polar. It implies that the electrons aren’t shared equally between the boron and fluorine atoms in BF3 molecule, but are instead electron in the covalent bond drawn towards fluorine (F) of BF3 molecule.

However, we must note here that bond polarity of B-F bond differs from the polarity of the entire BF3 molecule. Overall BF3 molecular polarity is not necessarily determined by bond polarity. It is mainly determined on a structural basis of BF3 molecule.

In this blog, we discussed about the polarity of NH3, BeCl2, SF4, XeF4, CH2Cl2 and many more.

Dipole Moment of BF3 Molecule

Since the three B-F bonds in BF3 (Boron Trifluoride) are polar, they have a definite bond dipole moment in their molecular geometry.

A bond dipole moment in BF3 molecule develops when a bond acquires polarity, i.e. when charge separation occurs in BF3 molecule. It is a measurement of the polarity of a Boron and Fluorine bond in BF3 molecule.

Chemists portray the dipole moment by using a slightly different arrow sign with the arrowhead pointing towards the negative Fluorine atom center and tail pointing to Boron atom, as shown:

B δ+ ———————> F δ-

Since the dipole moment of BF3 molecule is a vector quantity of both definite magnitude and specific direction, the dipole of BH3 molecule can also be 0 (Zero) when the two opposite bond dipoles cancel each other due to the molecule’s symmetrical geometry of BF3.

The Debye Unit, abbreviated as ‘D,‘ is used to calculate it. 1 D = 3.33564 10-30 C.m, where C stands for Coulomb and m for meter. To measure the dipole moment of BF3 molecule, we need to know the BF3 molecule’s shape (structural symmetry) and composition. The dipole moment of a bond B-F of BF3 molecule can be determined mathematically using the formula below:

Dipole Moment of B-F bond (µ) = Charge on boron and fluorine (Q) * distance of separation of B and F atoms (r)

BF3 molecule may have all of its B-F bonds be polar but still be nonpolar in nature. since the dipole moments of all of the B-F bonds cancel out each other, leaving the resulting dipole moment equal to 0. (Zero).

Now that we understand the concepts, we can see how the BF3 molecule is non-polar in nature despite the presence of F (Fluorine), a highly electronegative product.

However, as previously discussed, the highly symmetrical structure and geometry of BF3 (Boron Trifluoride) allows the B-F bond dipole moments to be canceled, resulting in a Molecular Dipole Moment of BF3 molecule is 0 (Zero). Thus, making the molecule BF3 (Boron Trifluoride) is nonpolar.

We now know that BF3 molecule’s non-polarity is due to its highly symmetrical Trigonal Planar geometry, as predicted by the VSEPR (Valence Shell Electron Pair Repulsion) Theory, which other molecules, such as H2O, lack.

BF3 Hybridization

Hybridization refers to the process of combining atomic orbitals of Boron and Fluorine atom to create new hybrid molecular orbitals. They can describe molecular geometry and nuclear bonding properties with ease. SP3, SP2, and SP hybridization are examples of different forms of hybridization of molecule. It is SP2 for this BF3 molecule because the double bond between the Boron atoms needs only one (pi) bond and only three bonds are formed per Boron atom. BF3 molecule undergoes SP2 hybridization.

Back bonding of BF3 molecule:

The length of the B–F bonds (1.30) in the boron trifluoride, BF3, is shorter than would be expected for single bonds in the BF3 molecule, suggesting that the fluoride has stronger B–F bonding. A simple explanation is the symmetry-enabled overlap of a p orbital on the boron atom with the in-phase combination of the three similarly oriented p orbitals on fluorine atoms.This behaviour of BF3 molecule is called back bonding in B-F bond.

Preparation of BF3 molecule:

Generally in industries BF3 prepared from the reaction between Boron oxide and hydrogen fluoride(HF). This is a best example of fluorinating reaction on the oxides.

B2O3 + 6 HF —> 2 BF3 + 3 H2O (exothermic reaction)

It should be used in anhydrous form as a reagents in the organic synthetic reactions. Mixing BF3 with diethyl ether forms an adduct compound of boron trifluoride etherate.

BF3 + diethyl ether ——-> Boron trifluoride etherate (Adduct compound)

Some organic reaction release BF3 by decomposing its diazonium salts of BF4-.

PhN2+BF4- —–> PhF + BF3 + N2

This method used in the organic synthetic laboratories.

BF3 and NH3 reaction:

BF3 is a Lewis acid and ammonia(NH3) is a Lewis base. According to Lewis law, “if any molecule donates an electron, it behaves as a bases”. In the reverse way, if any molecule accept the electron, it behaves as an acid”

Ammonia donates its excess lone pairs of electron to electron deficient BF3 molecule by forming the reaction as follows:

NH3 (Lewis base) + BF3 (Lewis acid) ———> NH3:BF3

Properties of BF3

Boron Trifluoride is poisonous in its gaseous state, but due to its high solubility, it dissolves quickly in cold water and produces Hydrofluoric Acid, which is extremely corrosive.
Metals, like stainless steel, can be corroded by it. It is 106 percent soluble in cold H2O ( 332 g of BF3/100 g water at 0 °C temperature.
Since BF3 vapours are heavier than air(critical pressure 49.85bar) , prolonged exposure of BF3 containers to heat or fire can result in a bursting or rocketing effect.
While colourless, it produces dense white fumes in moist air due to the presence of H2O molecules, but it is stable in a dry environment and anhydrous form.
As BF3 is heated for decomposition, toxic and corrosive Hydrogen Fluoride fumes are released into the air.
Unsaturated compounds can also be polymerized with BF3 (Boron Trifluoride). It is used as polymerization reagents. Some salt of BF3 used in the Suzuki coupling reactions.

Uses of BF3

Boron trifluoride (BF3) is used in a variety of industries applications. It’s used in automotive processing, the plastics industry, drug manufacture, and more as adhesives and sealant chemicals, adsorbents and absorbents, fuels and fuel additives, oxidizing/reducing agents, and binding agents. BF3 (Boron Trifluoride) is also used in the paper processing industry to make pulp processing.

It’s also used as a lubricant in engines, brake fluids, and oils, among other things. It can also be used to make oils, palm oil, crude petroleum, refined oil products, fuel oils, drilling oils, and so on.

The most common application of BF3 (Boron Trifluoride) is in organic synthesis, where it serves as a catalyst for a variety of reactions that are useful in industrial processes. The following are a few of them:

Friedel-Crafts alkylation reactions along with AlCl3 catalyst
Cleavage of ethers to alcohols: It takes place by decomposing boron trifluoride etherate adduct.
Esterification reactions: This type of reaction takes place between organic acid and alcohol.
Suzuki coupling reaction: This is the reaction used to form a covalent C-C bond between two different molecules. It is a very common reagent in modern organometallic reactions as a catalyst.

Conclusion

By now, you should have a good understanding of the principle of polarity and non-polarity in molecules, as well as the reasons why BF3 (Boron Trifluoride) is non-polar. We discussed the Lewis structure, Molecular geometry, Dipole moment, hybridization, Back bonding of BF3, properties and uses of BF3 as a best organic reagent. If you have any questions or are confused about something, please leave them in the comments section below. We will respond as quickly as possible.

FAQ on “BF3 polar or nonpolar”

Does BF3 have polar bonds

yes, all three B-F bonds are polar in nature.

What bond is BF3 ionic, polar or nonpolar ?

B-F bond is polar in nature. But the entire BF3 molecule is nonpolar.

Why is BF3 nonpolar and NF3 is polar?

In their uncombined state, boron is a metal and nitrogen is a gas; BF3 bonds have no dipole moment, while NF3 bonds do; boron’s atomic size is smaller than nitrogen’s; BF3 is a symmetrical molecule, while NF3 is unsymmetrical. As a result, NF3 is polar while BF3 is non-polar.