Bromine trifluoride (BrF3) Lewis dot structure, molecular geometry or shape, electron geometry, bond angle, formal charges, hybridization, polar vs non-polar
Bromine trifluoride represented by the formula BrF3 is an interhalogen chemical compound that appears as a yellowish, fuming liquid with a pungent odor. It is corrosive in nature. BrF3 inhalation for long time periods is toxic for human body cells. It is used as a fluorinating agent and as a fuel for nuclear reactors, rockets, and missiles.
In this article, we have discussed valuable information about the BrF3 molecule including how to draw its Lewis dot structure, what is its molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polarity, etc.
So, if you are curious to know about BrF3 chemistry, then what are you waiting for? Dive into the article and let’s start reading!
The Lewis structure of BrF3 consists of a bromine (Br) atom at the center. It is bonded to 3 atoms of fluorine (F), one on each side of the molecule. There are a total of 5 electron pairs around the central Bromine atom. Out of these 5 electron pairs, there are 3 bond pairs and 2 lone pairs in lewis structure of BrF3.
Drawing the Lewis structure of BrF3 is quite an easy task. Let’s see how we can do so by following the simple steps given below.
Steps for drawing the Lewis dot structure of BrF3
1. Count the total valence electrons in BrF3
The Lewis dot structure of a molecule is referred to as a simplified representation of all the valence electrons present in it. Therefore, the very first step while drawing the Lewis structure of BrF3 is to calculate the total valence electrons present in the concerned elemental atoms.
The two different elements present in BrF3 are bromine (Br) and fluorine (F). Both of these elements are halogens from Group VII A of the Periodic Table. So, both Br and F atoms contain 7 valence electrons each.
∴ The BrF3 molecule consists of 1 bromine atom and 3 atoms of fluorine. Thus, the total valence electrons available for drawing the Lewis structure of BrF3 = 7+7(3) = 28 valence electrons.
2. Find the least electronegative atom and place it at the center
The leastelectronegative atom is most likely to share its electrons with the atoms in its surroundings. Therefore, such an atom is placed at the center of the Lewis structure of a molecule.
Fluorine (F) is the most electronegative atom in the Periodic Table.
Thus, Bromine (Br) is less electronegative than fluorine, and consequently, it is placed at the center of the BrF3 Lewis structure. All the 3 F-atoms are placed in their surroundings.
3. Connect outer atoms with the central atom
The bromine atom is the central atom in the BrF3 while the fluorine atoms are the outer atoms. So, in this step, we connect the three F atoms with the central Br atom using single straight lines.
Each straight line represents a single covalent bond containing a bonded pair of electrons i.e., 2 electrons. There are a total of 3 single bonds in the BrF3 molecule, so the total valence electrons used so far are 3(2) = 6 valence electrons.
Total valence electrons available – electrons used till step 3 = 28 – 6 = 22 valence electrons.
This means we still have 22 valence electrons to be accommodated in the Lewis structure of BrF3.
4. Complete the octet of outer atoms
The F atoms are the outer atoms in the Lewis structure of BrF3. Each F atom requires a total of 8 valence electrons in order to achieve a stable octet electronic configuration.
There are three Br-F bonds in the BrF3 Lewis diagram drawn till now. This means each F atom already contains 2 valence electrons, so it needs 6 more electrons to acquire a complete octet.
Thus, 6 valence electrons are placed as 3 lone pairs around each F atom in the structure drawn below.
5. Place the remaining electrons as lone pairs on the central atom
Total valence electrons used till step 4 = 3 single bonds + 3 (electrons placed around each F atom, shown as dots) = 3(2) + 3(6) = 24 valence electrons.
Total valence electrons available – electrons used till step 4 = 28 – 24 = 4 valence electrons.
Thus, these 4 valence electrons are placed as 2 lone pairs around the central Br atom in the BrF3 Lewis structure as shown below.
In this way, the bromine (Br) in the BrF3 Lewis structure has a total of 10 valence electrons. It falls under the expanded octet rule. Bromine (Br) having d-subshells can accommodate more than 8 valence electrons during chemical bonding.
As a final step, we just need to check the stability of the above Lewis structure and we can do so by using the formal charge concept.
6. Check the stability of the BrF3 Lewis structure using the formal charge concept
The less the formal charge on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charge can be calculated using the formula given below.
What are the electron and molecular geometry of BrF3?
The ideal electron geometry of the bromine trifluoride (BrF3) molecule is trigonal bipyramidal. But it is due to the 2 lone pairs of electrons present on the central bromine atom that the molecule adopts a different molecular geometry or shape from its ideal electron geometry i.e., T-shaped.
Molecular geometry of BrF3
BrF3 is a T-shaped molecule. Two lone pairs situated on the central bromine atom in the BrF3 molecule set up a lone pair-lone pair and lone pair-bond pair repulsive effect which distorts the symmetry of the molecule. Consequently, the molecule adopts an asymmetric T-shape.
The 2 lone pairs occupy the equatorial positions while the 3 F-atoms lie at axial positions in order to minimize the electron-repulsive effect.
Electron geometry of BrF3
There are a total of 5 electron density regions around the central Br atom in the BrF3 molecule. According to the VSEPR concept, its ideal electron geometry is trigonal bipyramidal.
The electron geometry depends on the total number of electron density regions around the central atom i.e., total electron pairs in this case. It does not take into account whether an electron pair is a bond pair or a lone pair unlike that important for molecular geometry.
A more straightforward way of determining the shape and geometry of a molecule is to use the AXN method.
AXN is a simple formula to represent the number of atoms bonded to the central atom in a molecule and the number of lone pairs present on it.
It is used to predict the geometry or shape of a molecule using the VSEPR concept.
AXN notation for the BrF3 molecule
A in the AXN formula represents the central atom. In BrF3, bromine (Br) acts as the central atom so A = Br.
X denotes the atoms bonded to the central atom. 3 F atoms are bonded to the central Br atom in the BrF3 molecule thus X=3.
N stands for the lone pairs present on the central atom. As 2 lone pairs are present on central bromine in BrF3 thus N=2.
So, the AXN generic formula for the BrF3 molecule is AX3N2.
Now have a quick look at the VSEPR chart given below to identify where you find AX3N2.
The VSEPR chart confirms that molecules with an AX3N2 generic formula have a T-shape while their ideal electron geometry is trigonal bipyramidal, as we already noted down for the BrF3 molecule.
Hybridization of BrF3
The central bromine (Br) atom is sp3d hybridized in the BrF3 molecule.
The electronic configuration of bromine is [Ar] 3d104s24p5.
During chemical bonding, one 4p electron of bromine gets excited and shifts to an empty 4d atomic orbital. The 4s, three 4p, and one 4d atomic orbitals of bromine then hybridize to yield five sp3d hybrid orbitals.
Two of these five hybrid orbitals contain paired electrons. These paired electrons are situated as lone pairs on the central Br atom in BrF3.
The other three sp3d hybrid orbitals contain a single electron each which they use for sigma bond formation with the p orbitals of fluorine atoms in BrF3, as shown below.
A short trick for finding the hybridization present in a molecule is to memorize the table given below. You can find the steric number of a molecule and use that against this table to find its hybridization.
The steric number of central Br in BrF3 is 5 so it has sp3d hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The BrF3 bond angle
The ideal F-Br-F bond angle is 90° but it is due to the electronic repulsions and distortion present in the molecule that the F-Br-F bond angle decreases. Thus, the F-Br-F bond angle in BrF3 is approx. 86.2°.
There are two different bond lengths in the bromine trifluoride molecule i.e., a short Br-F bond length of 172 pm and two longer Br-F bond lengths of 181 pm. Refer to the figure below.
Fluorine (F) is a highly electronegative element. An electronegativity difference of 1.02 units exists between the bonded fluorine (E.N = 3.98) and bromine (E.N = 2.96) atoms in each Br-F bond in the BrF3 molecule. Thus, each Br-F bond is polar.
The asymmetrical T-shape of the BrF3 molecule maintains this polarity effect. The dipole moments of Br-F bonds do not get canceled. Rather, their effect adds up. In conclusion, the BrF3 molecule is polar with a net dipole moment μ > 1.19 D.
The Lewis structure for bromine trifluoride (BrF3) displays a total of 28 valence electrons i.e., 28/2 = 14 electron pairs.
Out of these 14 electron pairs, there are 3 bond pairs and 11 lone pairs.
2 lone pairs of electrons are present on the central Br atom while 3 lone pairs are present on each F-atom.
Why is the shape of BrF3 different from its ideal electron pair geometry?
There are 2 lone pairs of electrons present on the BrF3 molecule. The presence of these lone pairs leads to lone pair-lone pair and lone pair-bond pair electronic repulsions.
The repulsive effect distorts the shape and geometry of the molecule. Thus, BrF3 occupies a T-shape as opposed to an ideal trigonal bipyramidal electron geometry.
What is the geometry and shape of BrF3?
BrF3 possesses a T-shape or molecular geometry.
Is BrF3 tetrahedral?
No. The molecular geometry or shape of BrF3 is T-shaped while its ideal electronic geometry is trigonal bipyramidal.
What are the shapes of BrF3, BrF4–, XeOF2, H2O, and H2S?
The bromine trifluoride (BrF3) molecule has a T-shape. Three F-atoms are bonded to the central Br atom in BrF3 and it has 2 lone pairs of electrons.
The bromine tetrafluoride (BrF4–) ion has a square planar shape. Four F-atoms are bonded to the central Br atom in BrF4– and it has 2 lone pairs of electrons.
The xenon oxydifluoride (XeOF2) molecule has a T-shape, similar to BrF3. Two F-atoms and one O-atom are bonded to the central Xe atom and it has 2 lone pairs of electrons.
Both water (H2O) and dihydrogen sulfide (H2S) molecules have a bent shape.
The total valence electrons available for drawing the bromine trifluoride(BrF3) Lewis structure are 28.
The BrF3 molecule has a T-shape and molecular geometry.
The ideal electron geometry of BrF3 is trigonal bipyramidal.
It is due to the presence of 2 lone pairs on the central bromine atom in the BrF3 molecule that it adopts a distorted shape, different from its ideal electron pair geometry.
The central Br atom is sp3d hybridized in BrF3.
The F-Br-F bond angle is 86.2°, and the Br-F bond lengths are 172 pm and 181 pm respectively.
The BrF3 molecule is overall polar (net µ = 1.19 D).
Zero formal charges are present on both Br and F atoms in the BrF3 molecule ensuring the stability of its Lewis structure.
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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