Bromite ion (BrO2-) lewis structure, molecular geometry, oxidation number, hybridization
Bromite ion produced by the deprotonation of bromous acid, it has a chemical formula BrO2–, it is a monovalent inorganic anion. It appears as a yellow unstable crystal.
In this article, we will discuss BrO2– lewis structure, molecular geometry, hybridization, formal charges, etc.
Bromite ion is made by reacting the bromous acid with a base, it’s also called the conjugate base of a bromous acid.
BrO2– Lewis structure is made up of two oxygen (O) atoms, and one bromine (Br) atom. The bromine (Br) atom is the central atom in the lewis structure. The lewis structure of BrO2– contains one single bond, one double bond, and a total of 7 lone pairs.
Let’s see how to draw the lewis structure of BrO2– with a simple approach.
Follow some steps for drawing the lewis structure of BrO2–
⇒ Total number of the valence electrons in bromine = 7
∴ Total number of valence electron available for the BrO2– lewis structure = 7 + 6(2) + 1 = 20 valence electrons [∴ one bromine, two oxygen and one negative ion in BrO2– 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 BrO2– 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 as terminal atoms.
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, two single bonds are used.
Therefore, (2 single bonds × 2 electrons) = 4 valence electrons are used in the above structure from a total of 20 valence electrons available for the BrO2– lewis structure.
∴ (20 – 4) = 16valence electrons
Hence, we are left with 16 valence electrons more.
4. Complete the octet of the 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 BrO2– molecule, oxygen atoms are outer atoms and they need 8 electrons to complete their outer shell.
As you see in the above structure, we put the 6 electrons represented as dots on both oxygens. Now Oxygen atoms completed their octet, since, both have 8 electrons(6 represented as dots + 2 electrons in a single bond).
Again count the total valence electrons used in the above structure.
In the above structure, (2 single bonds mean 4 electrons + 12 electrons represented as dots) = 16 valence electrons are used from the total of 20 electrons available for BrO2- lewis structure.
∴ (20 – 16) = 4 valence electrons
Now we are left with only 4 valence electrons.
5. Complete the octet of the central atom
Bromine is the central atom in BrO2– molecule. And we have 4 remaining valence electrons, hence, put these remaining valence electrons over the Bromine central atom.
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(electrons represented as dots + electrons in a single bond) in their outer shell.
Also, we used all 20 valence electrons that are available for BrO2–.
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
⇒ Nonbonding electrons on bromine = 4
⇒ Bonding electrons around bromine = 4 (two single bonds)
∴ Formal charge on bromine atom = (7 – 4 – 4/2) = +1
For oxygen atom –
⇒ Valence electron of oxygen = 6
⇒ Nonbonding electrons on oxygen = 6
⇒ Bonding electrons around oxygen = 2 (one single bond)
∴ Formal charge on oxygen atom = (6 – 6 – 2/2) = -1
The above structure is not stable as it has an uneven formal charge. We have to lower the formal charge of the above structure.
To reduce the formal charge, We have to convert the one lone pair of oxygen atoms to form a double bond with the central atom.
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.
As you see, we reduced the formal charges, and the overall formal charge in the above figure is -1. Since, BrO2– has one negative ion as well, therefore, the entire structure should have a -1 formal charge.
BrO2– lewis structure
As BrO2– molecule contains one negative ion also, so, we need to put the bracket around the BrO2– lewis structure and show a negative ion outside the bracket.
The molecular geometry of BrO2–is Bent. The Bromine (Br) central atom is attached to two oxygen (O) atoms, also, it contains two lone pairs as well. According to VSEPR theory, it will form an AX2N2 type molecule, which implies its molecular geometry will be bent.
A represent the central atom
X represents the number of bonded atom to the central atom
N represent the lone pair on the central atom
The electron geometry for BrO2– will be tetrahedral. Since the Bromine central atom has 4 regions of electron density(2 lone pairs + 2 bonded atoms), it implies, its electron domain geometry will be tetrahedral.
Take a look at the VSEPR chart to understand the molecular and electron geometry of BrO2–.
Hybridization of BrO2–
Apply steric number formula to get the hybridization for BrO2– molecule.
“Steric number is the number of atoms bonded to a central atom of a molecule plus the number of lone pairs on the central atom”
∴ Steric number of Bromine in BrO2– molecule = (Number of bonded atoms attached to bromine + Lone pair on bromine)
∴ Steric number of BrO2– = (2 + 2) = 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 for Bromine in BrO2– molecule.
FAQ
What is the Oxidation number of Bromine in BrO2– molecule?
We know the oxidation number of oxygen is usually -2.
In BrO2– molecule, there are two oxygen atoms, also, one negative ion as well.
“In an ion, all oxidation numbers must be added to the charge on the ion.”
Let the oxidation number for Bromine be x.
∴ x + 2(-2) = -1
∴ x = -1 + 4
X = +3
The Bromine has a +3 oxidation number in BrO2– molecule.
How many lone pair do BrO2– lewis structure contains?
Lone pair electrons are represented as dots in the lewis diagram.
In BrO2– lewis structure, there are 14 dot electrons which means 7 lone pairs are present. 2 lone pairs on the bromine central atom, 3 on the single-bonded oxygen atom, and 2 on the double-bonded oxygen atom.
What is the formal charge in BrO2– lewis structure?
In the most stable lewis structure of BrO2–, the overall formal charge is -1.
The Bromine central atom has zero formal charges, double-bonded oxygen also has zero formal charges, the single-bonded oxygen atom has one formal charge.
What is the molecular shape of the BrO2– molecule?
The molecular shape of BrO2– is Bent, since, it is an AX2N2 type molecule that represents Bent molecular geometry.
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/
Topblogtenz is a website dedicated to providing informative and engaging content related to the field of chemistry and science. We aim to make complex subjects, like chemistry, approachable and enjoyable for everyone.
