When it comes to the polarity of a molecule, a simple question that strikes our mind considering BrF5 or (Bromine Pentafluoride as it is popularly known), is whether it’s a polar or non-polar molecule? As in Chemistry, the two main classes of molecules are divided into polar molecules and non-polar molecules.
Most of the time molecules can easily be declared polar or non-polar whereas, some of them are hard to identify in polarity. This is not the end as some molecules even fall somewhere on the spectrum scale between the two classes. Hence, some of the molecules face this issue in which BrF5 also falls.
So, Is BrF5 Polar or Non-Polar? 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. The molecule contains a central bromine atom which is encompassing a total of five fluorides and forming a lone pair of electrons. Therefore this molecule is ought to be polar.
This is a type of colorless, fuming liquid with a pungent odor that is mostly used as a fluorinating agent to produce fluorocarbons and also as an oxidizer in rocket propellant systems and is a very toxic chemical by inhalation.
It is Corrosive to metals and tissue. It has the ability to accelerate the burning of combustible material.
Before we dive deeper let’s clear a few terms and other important things as mentioned in the below subtopics.
How to identify a polar or non-polar molecule?
We can find this answer based on these terms:
- Polarity refers to the distribution of electric charges around atoms, molecules, or chemical groups.
- Polar molecules form when there is a difference in electronegativity between the bonded atoms.
- Non-polar molecules form when electrons are distributed equally between atoms of a diatomic molecule, or when the polar bonds in a bigger molecule can cancel each other out.
When does a Polar molecule form?
Polar molecules form when two atoms aren’t sharing electrons equally in a covalent bond.
Hence, dipole forms and a part of the molecule starts carrying a slight positive charge while the other part is carrying a slight negative charge.
This usually happens when there is a difference between the electronegativity value of each atom present in the molecule.
Example: H2O, NH3, SO2
Readout an interesting article about the polarity of SF2.
When does a Non-polar molecule form?
Non-Polar molecules form when two atoms are sharing electrons equally in a covalent bond.
In a non-polar covalent bond, the electrons are evenly distributed. In general, if the electronegativity difference falling between two atoms is less than 0.5, the bond is considered non-polar, (which is not in the case of BRF5).
Moreover, a molecule is truly non-polar when it is formed with identical atoms.
Non-polar molecules can also form when polar bond atoms are organized such that the electric charges can cancel each other out.
Example: He, H2, N2, CO2. For better understanding, go through the article related to the polarity of CF4.
So, on this behalf, BrF5 is Polar without a doubt!
Lewis dot structure of BrF5
The polarity is best concluded by first drawing a Lewis dot structure for BrF5.
The electron geometry of BrF5 in its Lewis structure is octahedral, and the hybridization is sp3d2. Next, as we draw the 3-d structure of BrF5 using the VSEPR rule.
Do keep in mind to draw the lone pair of electrons and you would see something great forming.
An asymmetrical charge distribution is visible in this molecule hence, proving that bromine pentafluoride (BrF5) is a polar molecule.
Why is BrF5 a polar molecule?
As we know bromine (Br) is a member of the halogen family, and it has seven valence electrons in total.
Lone Pair: if you see in its structure above, it shares around five of these electrons with covalently bonded fluorine (F) atoms, hence, leaving two electrons to freely form a lone pair at the top of this molecule.
As the lone pair is a region that is associated with a more negative charge, therefore, it becomes unbalanced as it is not having any atoms that have a positively charged nucleus, thus, the molecule is found to be polar.
Electronegativity: From the perspective of electronegativity, BrF5 consists of several polar covalent bonds as the significant difference between the electronegativity of bromine is (2.96) and fluorine is (3.98) which is greater in the electronegativity by .5 (even though both of them are halogens).
Usually, this difference where bromine falls short in electronegativity than fluorine comes out to play due to the number of layers of electrons shielding the nucleus in (Br) and hence, decreasing its pull on an average over its valence electrons.
Meanwhile, (F) Fluorine doesn’t have a huge number of layers when internal electrons are considered, hence, that could contribute to its shielding effect, therefore, proving that it has more electronegativity than Br or bromine (in fact Fluorine has the highest electronegativity as compared to any element on the periodic table!).
Thus the negative charge is distributed unequally!
What type of hybridization is used by BrF5?
As you can see in the first diagram, the central bromine atom is surrounded by six electron groups – a total of five bonding pairs and a single lone pair.
In most of the cases, the number of electron groups hanging around the central atom indicates the hybridization of that atom.
2 electron = sp
3 electron = sp²
4 electron = sp³
5 electron = sp³d
6 electron = sp³d²
Therefore, BrF5 has sp³d² hybridization.
Why is BrF5 covalent and not ionic?
The electronegativity difference between (Br) Bromine and (F) Fluorine is less than 1.7 as we have already discussed earlier and thus it is not ionic.
This electronegativity difference can only be achieved between a metal and a non-metal, whereas all the halogens are non-metals and therefore BrF5 is not ionic.
Does BrF5 have a dipole moment?
(BrF5), or bromine pentafluoride has a square pyramidal structure as in the first figure.
If we consider PCl5 which has a trigonal bi-pyramidal structure, there is no net dipole moment as the molecule is completely symmetric around the central phosphorus atom.
But, on the other hand, BrF5 does have a dipole moment due to the asymmetric structure as shown earlier in the figures.
Is BrF5 reactive?
Highly electronegative halogens are present in this molecular structure and due to this, the molecule will react with several organic substances including liquids like water (H2O).
As per the case studies in the 1950s and 60s, the molecule BrF5 was declared to be an extremely effective oxidizer (i.e. having the strength of removing electrons from molecules) which was possible due to the presence of several halogens in it.
However, this observation led to many difficulties later in handling and performing research experiments with this substance as it was required to be performed in a safe and effective manner.
Properties of BrF5
- Boron pentafluoride appears as a pale yellow in a liquid state.
- Its density is around 2.466 g/cm3.
- BrF5 has its very less melting point of −61.30 °C or −78.34 °F. therefore remains as a liquid at room temperature.
- Its boiling temperature is 40.25 °C or 104.45 °F.
- Its molecular mass is around 174.9 g/mol.
- It violently reacts with water.
The molecule BrF5 is a polar molecule as proven above via various illustrations and facts including its electronegativity difference between Br and F which is greater than 0.5(general electronegativity value).
Moreover, the molecular geometry of Bromine Pentafluoride is square pyramidal corresponding to an asymmetrical charge distribution on the central atom therefore, this molecule is polar as proven above.
We have also discussed here in the article that it is reactive and hence should be used with precautions. Although, it is mainly used in the aeronautical field for rocket propulsion. Hope this article helps you all!