BF3, also known as boron trifluoride, is an inorganic chemical compound that is a colorless gas with a pungent odor.
Students are often confused regarding the polarity or non-polarity of BF3 (Boron Trifluoride) due to the presence of three fluorine atoms which have a very high electronegativity value compared to the boron atom.
So is BF3 polar or non-polar?BF3 (boron trifluoride) is nonpolar due to its highly symmetrical shape. It has a trigonal planar geometry that cancels the dipole moments of the three BF bonds, making the resulting dipole moment of the compound equal to 0 (zero).
Let's try to understand this in some detail. To answer our question, let's look at several factors, responsible for polarity, with respect to BF3.
Molecular structure of BF3 (Boron Trifluoride)
The BF3 molecule (boron trifluoride) has 1 atom of B (boron, atomic number: 5) and 3 atoms of F (fluorine, atomic number: 9). The valency of B (Boron) is 3 and of F (Fluorine) is 7, so the Lewis structure of BF3 can be drawn as shown in the figure:
We can see that each F (fluorine) atom has 3 lone pairs of electrons, so the molecular structure is balanced and symmetrical.
According to the VSEPR (Valence Shell Electron Pair Repulsion) theory, the BF3 (boron trifluoride) molecule has a trigonal planar geometry with each F-B-F bond angle equal to 120 degrees, again adding to the equilibrium of the molecule making it the highly symmetric, as shown:
Electronegativity and binding polarity of BF3 (boron trifluoride)
In the BF3 molecule (boron trifluoride) there are three B-F bonds, as clearly shown in the Lewis diagram above.
The electronegativity of B (Boron) is 2.04 and of F (Fluorine) is 3.98 (maximum) according to the Pauling scale, which means that F (Fluorine) will attract shared electrons to itself and thus acquire a charge partial negative (δ-) and B (Boron) will have a partial positive charge (δ+).
To determine whether a bond is polar or not, we must find the difference between the electronegativity values of the two atoms sharing a bond.
The difference between the electronegativity values of B and F equals 1.94 (3.98 – 2.04 = 1.94), which is greater than 0.5.
Therefore, each B-F bond in the BF3 (boron trifluoride) molecule is polar. This means that the electrons are not shared equally by the two atoms (B and F), but are attracted to F (fluorine).
However, we must bear in mind that the polarity of the bond is different from the overall polarity of the molecule. Bond polarity does not always result in overall molecular polarity.
Dipole moment of BF3 (boron trifluoride)
The three B-F bonds in BF3 (boron trifluoride) are polar (as mentioned above) and therefore have a bond dipole moment as shown below:
But the highly symmetrical structure and geometry of BF3 (boron trifluoride), as discussed above, allows the bond dipole moments to be canceled so that the resulting molecular dipole moment equals 0 (zero).
Thus, making the BF3 (boron trifluoride) molecule apolar.
Now, we know that the nonpolarity of BF3 (boron trifluoride) is due to its highly symmetric trigonal planar geometry, as predicted by VSEPR (Valence Shell Electron Pair Repulsion) theory, that other molecules, such as H2O, Don't be afraid
To know whether a particular molecule is polar or non-polar, we must also understand the factors that are responsible for the polarity of a molecule. These factors are explained in detail below.
Molecular Structure and Geometry
The polarity of a molecule depends a lot on its structure and geometry. How the bond angle between the bonds determines whether the resulting dipole moment of the total molecule equals 0 (zero) or not.
The VSEPR (Valence Shell Electron Pair Repulsion) theory helps to identify the geometric shape of the molecule which gives us the bond angle.
The Lewis structure of the molecule gives us an overview of all the lone pairs of electrons that are present in the molecule.
If these lone pairs of electrons remain unbalanced, that is, asymmetrical, the molecule acquires a polarity (as in NH3, where the nitrogen atom has the lone pair).
Highly symmetric molecules are nonpolar (like BF3).
For more detailed information, you should also refer to the article written atLewis BF3 structure, molecular geometry and hybridization.
Electronegativity is denoted by the symbol χ (Greek letter Chi). It can be defined as the ability or strength with which an atom of an element attracts the shared electrons of a bond to itself, causing the distribution to be unequal.
The greater the electronegativity of an atom, the more likely it is to attract the shared electron pairs in a bond to itself.
It is decided by two factors, firstly the atomic number of the atom and secondly the distance that exists between the valence electrons of an atom and its positively charged nucleus.
Linus Pauling provided a periodic table of electronegativity for elements. Second, the element fluorine has the highest electronegativity equal to 3.98.
To know if a compound is polar or non-polar, we must first have an idea of what we mean by Polarity.
When atoms of different elements come together to form a compound, they do so by developing a bond between them. In this bond exchange of electrons occurs, but this exchange is not always the same between the elements.
The element with the highest electronegativity value attracts the shared electrons to itself, thus acquiring a partial negative charge (δ-), and the element with the lowest electronegativity value acquires a partial positive charge (δ+).
As a result, charge separation occurs within the bond and bond polarity develops. For a bond to be polar, the difference in electronegativity between the two atoms must be greater than or equal to 0.5.
However, the polarity of the bond alone does not make a molecule polar.
When a bond acquires polarity, that is, a charge separation occurs, a bond dipole moment develops. It is a measure of the polarity of the bond formed by two atoms.
Chemists represent the dipole moment with a slight variation on the arrow symbol with the arrowhead pointing toward the negative center, as shown:
d+ ———————> d-
As the dipole moment is a vector quantity, that is, it has magnitude and direction, it can also be 0 (zero) when the two opposite dipoles of the bond cancel each other out due to the symmetrical geometry of the molecule, as in BF3.
It is measured in Debye Units, denoted by 'D'. 1 D = 3.33564 × 10-30 C.m, where C is Coulomb and m represents one meter. To calculate the dipole moment we must know the shape and structure of the molecule. Mathematically, the dipole moment of a bond can be calculated using the following formula:
Dipole moment (µ) = Charge (Q) * separation distance (r)
A molecule can have all its bonds polar and still be nonpolar (like BF3), this happens due to the cancellation of the dipole moments of all bonds, making the resulting dipole moment equal to 0 (zero).
Now, with clear concepts in mind, we can clearly understand how the BF3 molecule is nonpolar despite the presence of F (Fluorine), a highly electronegative element.
Boron trifluoride is toxic when present in a gaseous state, but it dissolves easily in cold water due to its high solubility and gives hydrofluoric acid, which is highly corrosive in nature.
May corrode metals including stainless steel. Its solubility in cold H2O is 106%.
BF3 vapors are heavier than air and prolonged exposure of BF3 containers to heat or fire may cause rupture or explosion.
Although it is colorless, it forms dense white fumes in humid air due to the presence of H2O molecules, however, it is stable in dry atmosphere.
BF3 is also dangerous when heated through decomposition, producing toxic and corrosive hydrogen fluoride fumes.
BF3 (Boron Trifluoride) can also be used to polymerize unsaturated compounds.
Uses of BF3 (Boron Trifluoride)
BF3 (Boron Trifluoride) has many uses in various industries.
It is used as chemical adhesives and sealants, adsorbents and absorbents, fuels and fuel additives, oxidizing/reducing agents, binding agents for industrial manufacturing, plastics industry, medicine production, etc. (Source:https://www.epa.gov/chemical-data-reporting)
The paper industry also uses BF3 (boron trifluoride) to make pulp.
It is also used as engine lubricant, brake fuel, oil, etc. In addition, it is useful in making oils, crude oil, crude oil, refined petroleum products, fuel oils, drilling oils, etc.
The most important use of BF3 (Boron Trifluoride) is in organic synthesis as a catalyst for many reactions that are useful in industrial productions. Some of them are mentioned below:
- Friedel-Crafts alkylation reactions
- Cleavage of Ethers to Alcohols
- esterification reactions
- Nitration and sulfonation of aromatic compounds (Source: Brotherton RJ et al; Ullmann's Encyclopedia of Industrial Chemistry 7th ed. (1999-2012))
By now, you should have a clear understanding of the concept behind the polarity and nonpolarity of a molecule, including the specific reasons BF3 (boron trifluoride) makes it nonpolar.
If you have any queries or confusion regarding the same, feel free to drop your queries in the comments section below. We will contact you as soon as possible.