BrF5 is the chemical formula for bromine pentafluoride. Penta stands for five thus 5 Fluorine (F) atoms are covalently bonded to a bromine (Br) atom at the center of the bromine pentafluoride molecule.
BrF5 is a pale yellowish, fuming liquid with a pungent odor. Two different halogen atoms present in a single chemical compound lend it some unique physicochemical properties.
It is often used in the chemistry laboratory as a powerful fluorinating agent. Now the question that we are here to address is whether the BrF5 molecule is polar or non-polar. So, let’s find out.
Is BrF5 polar or nonpolar?
Bromine pentafluoride (BrF5) is a polar molecule. It is made up of five Br-F bonds. Each Br-F bond in the BrF5 molecule is polar due to a high electronegativity difference of 1.02 units between the bonded atoms.
The asymmetric square pyramidal shape of BrF5 with a lone pair of electrons present on the central Br atom further endorses the polarity effect. Thus, BrF5 is polar with a net dipole moment greater than 0.
The distribution of the shared electron cloud over the covalently bonded atoms of a molecule is called its electron density.
If a molecule’s electron density is uniformly balanced then such kind of molecule is called a nonpolar molecule.
Conversely, if the electron cloud distribution is not evenly balanced in different regions of the molecule then it is a polar molecule.
There will be a high electron density close to the negative pole of the molecule as opposed to its positive pole in a polar molecule.
Three main factors that control the electron cloud distribution and in turn the polarity of a molecule are:
Electronegativity
Dipole moment
Molecular shape or geometry
Let’s see how each of the above three factors makes bromine pentafluoride (BrF5) a polar molecule.
Factors affecting the polarity of BrF5
Electronegativity
Electronegativity is defined as the ability of an atom to attract a shared pair of electrons from a covalent bond.
According to Pauling’s electronegativity value –
A covalent bond is considered polar if the bonded atoms have an electronegativity difference of at least greater than 0.5 units.
However, you should keep in mind that no covalent bond is purely non-polar unless it is made up of two identical atoms such as H2, Cl2, Br2, etc.
Whenever a covalent bond is formed between two dissimilar atoms such as O and H in O-H or Br and F atoms in a Br-F bond, it will have some polar character.
Atom
Electronic configuration
Valence electrons
Bromine (35Br)
1s22s22p63s23p63d104s24p5
7
Fluorine (9F)
1s2 2s2 2p5
7
Bromine (Br) and fluorine (F) are both halogens that belong to group VII A (or group 17) of the Periodic Table. Both need one electron to achieve a stable octet electronic configuration. Therefore, they have a high affinity/ electronegativity toward the bonded electrons in a Br-F bond.
Still having said that, we know that the electronegativity of atoms decreases as we move down a group in the Periodic Table.
So, fluorine is more electronegative than bromine as the former lies above the latter in group VIIA. Fluorine is the most electronegative element of the periodic table.
Additionally, the atomic number of Br is 35 which means there are several layers of inner shell electrons between the Br nucleus and its valence electrons. The inner shell electrons cause a shielding effect, decreasing the pull of the Br atom on the shared Br-F electron pair.
The electronegativity of fluorine (3.98) is 1.02 units higher than the electronegativity of bromine (2.96). 1.02 units is greater than Pauling’s value of 0.5 so each Br-F bond in the BrF5 molecule is polar.
Both the atoms will have a firm grip on the Br-F bonded electrons, but Fluorine will more strongly attract the shared electron pair. Oppositely charged Brδ+ and Fδ- poles will develop in the molecule.
Dipole moment
The dipole moment (µ) is a vector quantity that is used to represent the magnitude as well as the direction of polarity in a polar bond or molecule.
The dipole moment arrow points from +Q to -Q as shown in the figure below.
The dipole moment of the polar bond points from the positive pole to the center of the negative pole. Therefore, in the BrF5 molecule, the dipole moment of each Br-F bond points from Brδ+ to Fδ-.
Each Br-F dipole moment has a value approximately equal to the electronegativity difference between Br and F atoms which is 1.02 D.
Molecular geometry
According to the Valence Shell Electron Pair Repulsion (VSEPR) theory of chemical bonding, BrF5 is an AB5E-type molecule. It is made up of a bromine atom at the center (A), surrounded by five fluorine atoms as bond pairs (B) and a lone pair (E) is present on bromine.
5 valence electrons of bromine get consumed in covalent bonding while the two remaining electrons are situated as a lone pair.
The ideal electronic geometry of an AB6 molecule is octahedral while the presence of a lone pair leads to lone pair-bond pair repulsions in the molecule.
This repulsive effect results in an asymmetric square pyramidal shape of the BrF5 molecule.
4 F atoms lie at the four corners of the square base, and 1 atom lies at the apex to form a pyramid while the lone pair is situated opposite this pyramid.
The dipole moments of individual Br-F bonds do not get canceled in the asymmetric BrF5 molecule. Rather, their effect adds up. Thus, BrF5 is a polar molecule with a non-uniformly distributed electron cloud. It has a net dipole moment of µ > 0.
BrF5 has polar Br-F bonds present due to an electronegativity difference of 1.02 units between bromine and fluorine atoms.
The asymmetric square pyramidal shape or molecular geometry of BrF5 further endorses this bond polarity.
Lone pair-bond pair repulsions lead to an asymmetric shape thus a non-uniformly distributed electron density over the molecule which makes BrF5 polar (net µ > 0).
“BrF5 or Bromine Pentafluoride is a polar molecule as the molecular geometry of BrF5 falls out to be square pyramidal with an asymmetric charge distribution concentrating on the central atom. “
What type of bonds is present in BrF5?
BrF5 possesses highly polarizable covalent bonds.
Which one is polar between BrF3 and BrF5?
Both bromine trifluoride (BrF3) and bromine pentafluoride (BrF5) are polar molecules.
In BrF3, three fluorine atoms are bonded to bromine at the center. There are two lone pairs present on the central atom. Lone pair-lone pair and lone pair-bond pair repulsions exist in the molecule.
The molecule occupies an asymmetric trigonal bipyramidal shape in which the electron cloud stays non-uniformly distributed thus BrF3 is polar with net µ =1.19 D.
Thus, Br achieves a valence shell electronic configuration of 4s1, 4px1 4py1 4pz1 and 4dxy1 4dyz1. All these orbitals hybridize to yield six sp3d2 hybrid orbitals.
Five of these sp3d2 hybrid orbitals contain a single electron each while the sixth orbital has paired electrons that are situated as a lone pair on Br.
The singly filled sp3d2 hybrid orbitals of Br form five sigma (σ) bonds with the p orbitals of F, one on each side of the square pyramidal molecule.
Summary
Bromine pentafluoride (BrF5) is a polar molecule.
It consists of five Br-F bonds. Each Br-F bond is polar due to a significant electronegativity difference between the bonded bromine and fluorine atoms.
Each Br-F bond has a specific dipole moment value.
The dipole moment effect of individual Br-F bonds adds up in the asymmetric square pyramidal shape of the molecule thus BrF5 is polar with net µ > 0.
The F-Br-F bond angle is 84.8° while the Br-F bond lengths are equal to 168.9 pm and 177.4 pm respectively in the BrF5
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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