Chlorate [ClO3]- ion Lewis dot structure, molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polar vs non-polar
[ClO3]– is the chemical formula for chlorine trioxide, more commonly known as the chlorate ion. The chlorate ion is present in chloric acid salts. It is a monovalent anion and a strong oxidizing agent therefore chlorate ion holds special importance in a chemistry student’s workbook.
If you want to learn about the Lewis dot structure of chlorate [ClO3]– ion, its molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, and polarity nature, then you are at the right place because we have discussed in this article all that and much more in detail.
The Lewis structure of a chlorate [ClO3]– ion consists of a chlorine (Cl) atom at the center, it is bonded to three atoms of oxygen (O) at the sides. There are a total of four electron density regions around the central Cl atom in [ClO3]–. Out of these 4 electron density regions, there are 3 bond pairs and 1 lone pair of electrons on the central Cl atom.
Drawing the Lewis dot structure of chlorate [ClO3]– ion is easy if you follow the following simple steps.
Steps for drawing the Lewis dot structure of [ClO3]–
1. Count the total valence electrons in [ClO3]–
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 [ClO3]– is to count the total valence electrons present in the concerned elemental atoms.
There are two different elemental atoms present in the chlorate ion i.e., a chlorine (Cl) atom and an oxygen (O) atom. We can determine the valence electrons present in them by identifying their position in the Periodic Table of elements.
Oxygen is present in Group VI A of the Periodic Table so it has a total of 6 valence electrons. Conversely, chlorine is present in Group VII A so it has a total of 7 valence electrons in each atom.
The [ClO3]– ion consists of 1 Cl-atom and 3 O-atoms. Thus, the valence electrons in the Lewis dot structure of [ClO3]– = 1(7) + 3(6) = 25 valence electrons.
However, the twist here is that the [ClO3]– ion carries a negative (-1) charge which means 1 extra valence electron is added in this Lewis structure.
∴ Hence, the total valence electrons available for drawing the Lewis dot structure of [ClO3]– = 25+1 = 26 valence electrons.
2. Choose the central atom
In the second step of drawing the Lewis structure of a molecule or a molecular ion, we need to place the least electronegative atom at the center.
As electronegativity refers to the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond therefore the least electronegative atom is the one that is most likely to share its electrons with other atoms in its surroundings.
As chlorine (Cl) is less electronegative than oxygen (O) so the chlorine atom is placed at the center of the [ClO3]– Lewis structure while the oxygen atoms are spread around it, as shown in the figure below.
3. Connect outer atoms with the central atom
In this step, we need to join the central Cl atom with the outer O atoms using single straight lines.
Each straight line represents a single covalent bond i.e., a bond pair containing 2 electrons. There are a total of 3 single bonds in the above diagram which means a total of 3(2) = 6 valence electrons are used till this step, out of the 26 initially available.
Total valence electrons available – electrons used till step 3 = 26-6 = 20 valence electrons.
This means we still have 20 valence electrons to be accommodated in the Lewis dot structure of [ClO3]–.
4. Complete the octet of outer atoms
As we already identified, the three oxygen atoms act as outer atoms in [ClO3]– Lewis structure and each Cl atom needs a total of 8 valence electrons in order to achieve a stable octet electronic configuration. Single Cl-O bonds on each side of the [ClO3]– Lewis structure means all the outer O atoms already have 2 electrons each. Thus, all three O atoms require 6 more electrons to complete their octet.
Thus, these 6 electrons are placed as 3 lone pairs around each outer Cl atom in [ClO3]– Lewis structure, as shown in the figure below.
5. Complete the octet of the central atom
Total valence electrons used till step 4 = 3 single bonds + 3 (electrons placed around each O atom, shown as dots) = 3(2) + 3(6) = 24 valence electrons.
Total valence electrons available – electrons used till step 4 = 26-24= 2 valence electrons.
So, these 2 valence electrons are now placed as a lone pair on the central Cl atom in the [ClO3]– Lewis dot structure.
In this way, the central Cl atom has a total of 3 single bonds and 1 lone pair of electrons which denotes a complete octet. Also, the octet of each outer O atom is complete with 1 single bond and 3 lone pairs each.
The last step is to check the stability of the Lewis structure obtained above. We can do that by using the formal charge concept.
6. Check the stability of the ClO3– 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.
This calculation shows that the central Cl atom contains a +2 formal charge while the outer O atoms contain a -1 formal charge each.
But, as we already discussed the fewer the formal charges present on bonded atoms, the greater the stability of a Lewis structure.
Hence we can minimize the formal charges by converting lone pairs into covalent bonds, let us explain to you how that is done, in the next step.
7. Minimize the formal charges by converting lone pairs into covalent bonds until a stable Lewis’s structure is obtained
The lone pairs of electrons present on any two outer O-atoms are now converted into covalent bonds between the central Cl atom and the concerned O-atoms as shown below.
In this way, the central Cl atom has a total of 1 single bond and 2 double covalent bonds. In other words, there is a single-bonded O-atom and two double-bonded O-atoms in this Lewis structure.
Now we can again check its stability using the formal charge concept.
For chlorine atom
Valence electrons of chlorine = 7
Bonding electrons = 1 single bond + 2 double bonds = 2 + 2(4) = 10 electrons
Thus, the formal charges present on the central Cl atom and two outer O-atoms are reduced to zero. However, a -1 formal charge is present on the third O-atom which accounts for the charge present on the chlorate ion.
Henceforth, the [ClO3]– Lewis structure is enclosed in square brackets and a negative 1 charge is placed at the top right corner, as shown below. This ensures that it is a correct and stable Lewis representation for the chlorate [ClO3]– ion.
The above Lewis structure shows that there are a total of 12 valence electrons around the central Cl-atom which means it has an expanded octet. This is possible because the chlorine atom has a 3d atomic orbital so it can possess more than 8 valence electrons during chemical bonding.
Another important point is that the actual structure of the chlorate ion is a hybrid of the resonance structures given below. Each resonance structure is a way of representing the Lewis structure of a molecule or a molecular ion. The resonance structures show that a double bond can be formed between the central Cl-atom and any two outer O-atoms in [ClO3]–.
Now, that we have discussed everything about chlorate ion Lewis structure, we are good to proceed to the next section of this article where we will talk about the shape and geometry of [ClO3]–.
What are the electron and molecular geometry of ClO3-?
The chlorate [ClO3]– ion has a trigonal pyramidal shape and molecular geometry while the ideal electron pair geometry of the ion is tetrahedral. There is a lone pair of electrons present on the central Cl-atom in [ClO3]–.
The lone pair-bond pair electronic repulsions distort the geometry and shape of the molecular ion and make it adopt a different shape from its electronic geometry.
Molecular geometry of [ClO3]–
The chlorate [ClO3]– ion has a trigonal pyramidal molecular geometry and shape. There is a lone pair of electrons present on the central chlorine atom in chlorate. Therefore, lone pair-bond pair electronic repulsions exist in the molecule in addition to bond pair-bond pair repulsions.
This repulsive effect distorts the shape of the molecule and makes it adopt a trigonal pyramidal shape. The lone pair is situated at the apex of a pyramid that has a triangular base, as shown below.
An important point to note is that the molecular geometry or shape of a molecule or a molecular ion strongly depends on the different number of bond pairs and lone pairs present on the central atom. However, the ideal electron pair geometry depends on the total number of electron pairs present on the central atom only, no matter whether it’s a bond pair or a lone pair.
Let us see how this concept is specifically applied to the chlorate [ClO3]– ion.
Electron geometry of [ClO3]–
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule or a molecular ion containing a total of 4 electron density regions around the central atom is tetrahedral.
In the chlorate [ClO3]– ion, there are 2 double bonds, 1 single bond, and 1 lone pair on the central chlorine atom which makes a total of 4 electron density regions. Thus it has a tetrahedral electron pair geometry.
An easy way to find the shape and geometry of the 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 [ClO3]– molecular ion
A in the AXN formula represents the central atom. In the [ClO3]– ion, chlorine is present at the center so A=Cl.
X denotes the atoms bonded to the central atom. In [ClO3]–, three oxygen (O) atoms are bonded to the central Cl so X=3.
N stands for the lone pairs present on the central atom. As per the Lewis structure of [ClO3]– there is one lone pair on central chlorine so N=1.
So, the AXN generic formula for the [ClO3]– ion is AX3N.
Now, you may have a look at the VSEPR chart below.
According to the VSEPR chart given above, the ideal electron geometry of a molecule or a molecular ion having AX3N generic formula is tetrahedral while its molecular geometry or shape is trigonal pyramidal, as we already noted down for the [ClO3]– ion.
Hybridization of [ClO3]–
The chlorate [ClO3]– ion has sp3 hybridization.
The electronic configuration of a chlorine (Cl) atom is 1s2 2s2 2p6 3s2 3p5.
The electronic configuration of the oxygen (O) atom is 1s2 2s2 2p4.
During chemical bonding, the paired 3p electrons of chlorine get unpaired and two of these electrons shifts to two separate empty 3d atomic orbitals. Consequently, the 3s orbital hybridizes with three half-filled 3p orbitals to yield four sp3 hybrid orbitals. Each sp3 hybrid orbital has a 25 % s-character and a 75% p-character.
Three of the four sp3 hybrid orbitals contain a single electron each while the fourth sp3 hybrid orbital contains paired electrons. These paired electrons are situated as a lone pair on the central Cl atom in the chlorate [ClO3]– ion.
One sp3 hybrid orbital containing a single electron forms a Cl-O sigma (σ) bond with the p orbital of oxygen by sp3-p overlap, on one side of the [ClO3]– ion.
The other two sp3 hybrid orbitals of chlorine form sigma (σ) bonds with the sp2 hybrid orbitals of oxygen in the Cl=O double bonds.
The unhybridized d orbitals of chlorine overlap with the unhybridized p orbitals of the oxygen atoms to form the required pi (π) bonds in the Cl=O double bonds of the chlorate ion.
A shortcut to finding the hybridization present in a molecule or a molecular ion is by using its steric number against the table given below. The steric number of central Cl in [ClO3]– is 4 so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The [ClO3]– bond angle
The ideal bond angle in a tetrahedral molecule is 109.5° but in the chlorate [ClO3]– ion, the lone pair present on the central chlorine atom distorts the shape and geometry of the molecular ion. It adopts a triangular pyramidal shape and consequently, the O-Cl-O bond angle decreases slightly from the ideal 109.5° to approx. 106.5°.
Although a Cl=O bond is expected to be stronger and shorter in length than a Cl-O bond. But, experimental results reveal that it is due to the resonance present in the chlorate ion that all three Cl-O bond lengths in [ClO3]– are approx. equal i.e., 148.7 pm.
Each Cl-O bond present in the [ClO3]– ion is slightly polar due to an electronegativity difference of 0.28 units between the covalently bonded chlorine (E.N = 3.16) and oxygen (E.N = 3.44) atoms. The Cl-O electron cloud stays largely towards the O atom as opposed to the Cl atom.
In consequence, each O atom gains a partial positive (δ+) charge while the central Cl atom attains a partial negative (δ-) charge in the chlorate ion. Each Cl-O bond thus possesses a specific dipole moment value (symbol µ).
The asymmetric trigonal pyramidal shape of the chlorate ion further enhances the dipole moment effect. Thus the chlorate [ClO3]– ion is overall polar with a non-uniformly distributed electron cloud and a net µ= 2.186 D.
The Lewis structure for [ClO3]– displays a total of 26 valence electrons i.e., 26/2 = 13 electron pairs.
Out of these 13 electron pairs, there are 5 bond pairs and 8 lone pairs.
Out of the 8 lone pairs of electrons, 1 lone pair is present on the central Cl atom.
The central Cl atom is bonded to two O-atoms via double covalent bonds and to the third O-atom via a single covalent bond.
There are 2 lone pairs on the double-bonded O-atoms while 3 lone pairs are present on the single-bonded O-atom.
What is the shape of [ClO3]– ion?
The AXN generic formula for the [ClO3]– ion is AX3N. So, according to the VSEPR concept, it has a trigonal pyramidal shape and molecular geometry.
What is the geometry of [ClO3]– according to hybridization?
The [ClO3]– ion has sp3 hybridization. There are a total of 4 electron density regions around the central Cl atom in the chlorate [ClO3]– ion. Therefore, its ideal electron pair geometry is tetrahedral.
However, it has a different shape and molecular geometry from its ideal electron pair geometry owing to the presence of a lone pair of electrons on the central Cl atom i.e., trigonal pyramidal vs tetrahedral.
How is the shape of chlorate [ClO3]– ion different from that of chlorite [ClO2]– ion?
In the chlorate [ClO3]– ion, three oxygen (O) atoms are bonded to a central Cl-atom. There is one lone pair of electrons on the central Cl-atom so it has a trigonal pyramidal shape while its ideal electron pair geometry is tetrahedral.
On the other hand, in the chlorite [ClO2]– ion, two oxygen (O) atoms are bonded to the central Cl-atom. There are two lone pairs on the central Cl-atom. Its ideal electronic geometry is the same as that for chlorate i.e., tetrahedral. However, it has a different shape due to lone pair-lone pair electronic repulsions i.e., V-shape or bent.
The total number of valence electrons available for drawing chlorate [ClO3]– ion Lewis structure is 26.
The negative 1 charge present on the chlorate ion accounts for 1 extra valence electron in its Lewis structure.
The [ClO3]– ion has a trigonal pyramidal shape and molecular geometry.
The ideal electron pair geometry of the chlorate [ClO3]– ion is tetrahedral.
The O-Cl-O bond angle is 106.5° while all the Cl-O bond lengths are 148.1 pm in [ClO3]–
It is due to the resonance present in the chlorate [ClO3]– ion that each Cl-O bond length is equivalent as opposed to two shorter Cl=O bonds and one longer Cl-O bond, as expected.
The central Cl-atom in [ClO3]– ion is sp3
The [ClO3]– ion is polar in nature. The absence of a plane of symmetry in the molecular ion further endorses the polarity effect. Thus, the electron cloud stays non-uniformly distributed overall (net µ>0).
-1 formal charge is present on a singly bonded O-atom in the [ClO3]– Lewis structure which makes the molecular ion occupy an overall charge of -1.
In conclusion, [ClO3]– is a monovalentpolyatomic anion.
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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