Bromate ion (BrO3-) lewis dot structure, molecular geometry, polar or non-polar, hybridization
Bromate is a bromine-based oxoanion that has a chemical formula BrO3-, it is a monovalent inorganic anion. It is denser than water. Bromate ion is formed when ozone reacts with bromide anion. It formed many salts like sodium bromate, potassium bromate, etc.
In this article, we will discuss BrO3- lewis structure, molecular geometry, hybridization, polar or nonpolar, etc.
Exposure to bromate ions can cause irritation to the eyes, skin, and other body parts. Long-term exposure can cause severe health hazards. BrO3- is a conjugate base of bromic acid.
BrO3- lewis structure is made up of one bromine (Br) and three oxygen (O) atoms. There is one lone pair on the central atom (bromine) and a total of 7 on the surrounding atom (oxygen). Also, the overall formal charge in BrO3- lewis structure is -1.
Let’s see how to draw the BrO3- lewis structure with a simple approach.
Follow some steps for drawing the lewis dot structure for BrO3-
1. Count total valence electron in BrO3-
Lewis diagram is a simple representation of the valence electron within a molecule. So, for determining the valence electron in BrO3-, look at the periodic group of bromine and oxygen atoms.
By looking at the periodic table, we get to know, bromine belongs to the 17th periodic group and oxygen to the 16th.
Hence, the valence electron for bromine is 7 and for oxygen, it is 6.
⇒ Total number of the valence electrons in bromine = 7
∴ Total number of valence electron available for the BrO3- lewis structure = 7 + 6(3) + 1 = 26 valence electrons [∴one bromine, three oxygen and one negative ion that also count as a one valence electron]
2. Find the least electronegative atom and placed it at center
In this step, we need to place the less electronegative atom in the BrO3- molecule at the central position, and rests are spaced evenly around it.
A bromine atom(2.96) is less electronegative than an oxygen atom(3.44), hence, put the bromine in the central position of the lewis diagram and oxygen spread evenly around it.
3. Connect outer atoms to central atom with a single bond
Now just attach the single bond for connecting each outer atom(oxygen) to the central atom(bromine).
Count the valence electron we used to draw the above structure. A single bond means two electrons and in the above structure, three single bonds are used to connect each outer atom to the central atom.
Therefore, 6 valence electrons (3 single bonds × 2 electrons) were used in the above structure from a total of 26 valence electrons available for the BrO3- lewis structure.
∴ (26 – 6) = 20valence electrons
Hence, we are left with 20 valence electrons more.
4. Place remaining valence electrons starting from outer atom first
Here’s we need to put our remaining valence electron over outer atoms first to complete their octet. In the case of the BrO3- molecule, oxygen atoms are outer atoms and they need 8 electrons in the outermost shell to achieve the octet.
As you see in the above structure, we put the 6 valence electrons on each outer atom (oxygen) as they already sharing two atoms with the help of a single bond. So, all these oxygen atoms have 8 valence electrons to share.
Therefore, the outer atoms in BrO3- molecule completed their octet comfortably.
We have used (6 electrons × 3 oxygen atom) = 18 valence electrons in the above structure from the total of 20 remaining valence electrons.
∴ (20 – 18) = 2 valence electrons
Now we are left with only 2 valence electrons.
5. Complete central atom octet and make covalent bond if necessary
As we already completed the octet for surrounding atoms, now we need to complete the octet for the central atom also.
As you see in the 4th stepstructure, bromine is the central atom that is attached to the three oxygen atoms with the help of a single bond. It means, it already shares 6 valence electrons through the 3 single bonds.
So, bromine needs only two electrons to complete the octet. As we already have 2 remaining valence electrons, so, just put these 2 over bromine.
If you look at the above structure, we see that all atoms(oxygen and bromine) completed their octet comfortably as each of them has 8 valence electrons to share.
Also, we used all 26 valence electrons that are available for BrO3-.
Now we just need to check the stability of the above structure through the formal charge concept.
6. Check the stability with the help of a formal charge concept
The structure with the formal charge close to zero or zero is the best and most stable lewis structure.
To calculate the formal charge on an atom. Use the formula given below-
We will calculate the formal charge on the 5th stepstructure to verify its stability.
For Bromine atom –
⇒ Valence electron of bromine = 7
⇒ Lone pair electrons on bromine = 2
⇒ Shared pair electrons around bromine = 6 (three single bonds)
∴ F.C. on bromine atom = (7 – 2 – 6/2) = +2
Each oxygen atom in the 5th stepstructure has 3 lone pairs and one bond pair, so, their formal charge will also be the same. Hence, just count the F.C. for one oxygen atom.
For oxygen atom –
⇒ Valence electron of oxygen = 6
⇒ Lone pair electrons on oxygen = 6
⇒ Shared pair electrons around oxygen = 2
∴ F.C. on oxygen atom = (6 – 6 – 2/2) = -1
Obviously, this structure is not stable as it attains a very high formal charge. We have to lower the formal charge of the above structure by converting some lone pairs to bond pairs (covalent bonds).
Note: Bromine atom is exceptional to the octet rule as it can hold more than 8 electrons in its outermost shell. It is also called an expanded octet.
Expanded octet: A case where an atom shares more than eight electrons with its bonding partners.
But oxygen atoms can only hold the 8 electrons, so, we will convert the lone pair of oxygen atoms to a covalent bond without violating its octet rule.
As you see in the above figure, we convert two lone pairs of oxygen atoms to a covalent bond for getting a formal charge on each atom close to zero or zero.
So, the final lewis structure of BrO3- contains two double bonds and one single bond, each oxygen atom has 8 valence electrons, and the bromine central atom has 12 valence electrons in its outermost shell as it has the ability to expand octet.
The overall charge in BrO3- is -1
BrO3- lewis structure
As BrO3- molecule contains one negative ion also, so, we need to put the bracket around the BrO3- lewis structure and show a negative ion outside the bracket.
The molecular geometry of BrO3- is trigonal pyramidal as its central atom(bromine) is attached to the three oxygen atoms and it contains one lone pair also, the lone pair presence on the bromine atom pushes all three oxygen atoms down because of repulsive force occurs between electron pairs according to the VSEPR theory.
So, the final shape of BrO3- appears like a trigonal pyramid.
According to the VSEPR theory, lone pair and bond pair electrons create repulsion and tried to remain far apart where repulsion becomes minimum between the electrons.
In the above structure, the lone pair on the bromine atom repels the adjacent bonded pair of electrons, hence, push them further down, giving trigonal pyramidal molecular geometry of BrO3-.
Theoretically, we can use an AXN method and VSEPR chart to determines the shape of BrO3-.
Now we have to find the molecular geometry of BrO3- by using this method.
AXN notation for BrO3- molecule:
A represents the central atom, so according to the BrO3- lewis structure, bromine is the central atom. A = Bromine
X represents the bonded atoms connected to the central atom, as we know, bromine is attached to three oxygen atoms. Therefore, X = 3
N represents the lone pair on the central atom, bromine atom has one lone pair on it. Hence, N = 1
So, the AXN notation for the BrO3- molecule becomes AX3N1.
So, as per the VSEPR chart, if the central atom of a molecule contains 1 lone pair and is covered by three surrounding atoms, then the molecular shape of that molecule is trigonal pyramidal in nature.
Hence, the molecular shape or geometry for BrO3- is trigonal pyramidal.
BrO3- molecular geometry
The electron geometry for BrO3- is tetrahedral.
Hybridization of BrO3-
According to the BrO3- lewis structure, the bromine central atom is attached to the three oxygen atoms, hence, makes a three-sigma bond and it contains one lone pair also.
Now just find the steric number of bromine central atom to determine the hybridization in the BrO3- molecule.
“Steric number is the number of atoms bonded to a central atom of a molecule plus the number of lone pairs attached to the central atom”
∴ Steric number of Bromine in BrO3- molecule = (Number of bonded atoms attached to bromine + Lone pair on bromine)
∴ Steric number of BrO3-= (3 + 1) = 4
Steric number
Hybridization
1
S
2
Sp
3
Sp²
4
Sp³
5
Sp³d
6
Sp³d²
So, for a steric number of four, we get the Sp3 hybridization in BrO3- molecule.
The bond angle of BrO3-
“A bond angle is the angle between two atoms in a molecule”.
The ideal bond angle for tetrahedral geometry that contains no lone pair is 109.5°, however, the presence of a lone pair contracts the bond angle slightly as it tries to repel other bonded atoms.
In BrO3- molecule, one lone pair is present on the bromine central atom, hence, it contracts the bonded atoms, and so does the bond angle also.
Therefore, the bond angle in BrO3- the molecule is less than 109.5º, and its actual bond angle is close to 104°.
So, Is BrO3- polar or nonpolar molecule? BrO3- is a polar molecule because it has an asymmetrical molecular shape causes by the presence of lone pair on the central atom, hence, the charges induced on atoms are unable to cancel out each other leading to some net dipole moment in the molecule.
The bond (Br-O) in BrO3- the molecule is polar because of the electronegativity difference between bromine(2.96) and oxygen(3.44).
The trigonal pyramidal geometry of the BrO3- molecule causes unequal distribution of charges on atoms, hence, canceling of dipole moment induced on these atoms becomes difficult.
Therefore, the presence of some net dipole moment in BrO3-, makes this molecule polar in nature.
Why the bromine central atom in BrO3- lewis structure, holds more than 8 electrons?
Whenever the d-orbitals and beyond to it, participate in bonding with other atoms then an expanded octet is produced.
Bromine atom in BrO3- lewis structure expanded the octet because it has d-orbitals in the third principal energy level, hence, it has extra orbital(d-orbital) for additional electron needed for bonding.
Sulfur, phosphorous, chlorine, and silicon are some other examples that can expand their octet and hold electrons more than 8.
How many shared pair and unshared pair electrons do BrO3- lewis structure contains?
Shared pair electrons are called bonded pair electrons that take part in chemical bonding to share the electrons whereas unshared electrons are called lone pair electrons that don’t form the chemical bond.
According to the BrO3- lewis structure, 10 shared pair electrons(2 double bonds + one single bond) and 16 unshared electrons(8 lone pairs) are present.
The total valence electron available for drawing the Bromate ion (BrO3-) lewis structure is 26.
BrO3- lewis structure has two double bonds (Br=O), and one single bond (Br-O). The bromine (Br) atom is in the central position and the oxygen (O) atoms are in the surrounding position.
The hybridization in BrO3- is Sp3.
The bond angle in bromate ion is around 104º.
BrO3- is a polar molecule because of its the distorted shape that leads to some net dipole moment in it.
The overall formal charge in BrO3- is -1.
The molecular geometry of BrO3- is trigonal pyramidal.
A total of 16 lone pairs of electrons and 10 bonded pairs of electrons are present in BrO3- 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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