In ionic form chlorine dioxide is known as chlorite with the molecular formula (ClO2-). It is clear from the chemical formula that chlorine dioxide or chlorite is a strong oxidizing agent. Chlorine dioxide tends to get reduced and provide oxygen to different substrates during an oxidation-reduction or redox reaction. From this, it can be understood that chlorine dioxide in an ionic state will be a strong oxidizer of chlorine oxyanions. Recently, this compound was in limelight due to a fraudulent claim to cure coronavirus. Let us study this compound in more detail.  

Lewis Structure of Chlorine Dioxide (ClO2-)

The Lewis structure is a pictorial representation of valence electrons taking part in the formation of bonds to produce a new molecule with new properties altogether. To begin drawing the Lewis structure of Chlorine dioxide, first, it is essential to draw one for the participating elements. For Chlorine, Atomic number = 17 Electronic Configuration = 1s2 2s2 2p6 3s2 3p5 Valence Electrons = 7 For Oxygen, Atomic number = 8 Electronic Configuration = 1s2 2s2 2p4 Valence Electrons = 6

Now, it will be easier to draw the Lewis structure of chlorine dioxide as we know that there are 20 valence electrons in one chlorine dioxide molecule. It might confuse many people as ClO2 comprises 19 valence electrons only. Here, it is crucial to understand that chlorine dioxide is a strong anion and oxidizing agent. This arises from the fact that chlorine dioxide is an unstable molecule and mainly exists as ClO2- during bond formation. Due to this, the valence electrons in chlorine dioxide or chlorite are 20. We will draw the Lewis structure of chlorine dioxide with 20 valence electrons. Let us follow some steps to draw the Lewis structure of chlorine dioxide: Step 1: Find the total valence electrons in one molecule of chlorine dioxide. It is 20 as chlorine has 7 valence electrons and oxygen has 6 valence electrons. There are two oxygen molecules in chlorine dioxide so the total is 19. But chlorine dioxide exists as ClO2- during the formation of a bond, therefore we have one more valence electron available. So, the total number of valence electrons available in one chlorine dioxide or chlorite molecule is 20. Step 2: Find the valence electrons further needed to stabilize the molecule. By the octet rule, each element needs eight valence electrons to complete its electronic configuration. Here, an anomaly exists with the chlorine atom as it can increase its octet to accommodate more valence electrons. It is a classic example of chemistry being full of exceptions! Chlorine belongs to the third group in the periodic table. The third group has the ability to expand its octet and accommodate more valence electrons to achieve a stable molecular structure. Hence, with no anomaly, the total valence electrons required by one chlorine dioxide would have been 24 which is now 26 with the anomaly of expanded octet in chlorine atom. Step 3: Draw the skeleton of chlorine dioxide.

The aforementioned diagram is one of the lewis structures of chlorine dioxide but, we need to check its stability with the help of formal charge distribution. The reason for the same is each molecule wants to achieve a stable structure that can be gained only with zero formal charge distribution. Now we need to calculate the formal charge distribution on chlorine dioxide molecule: Formal Charge = Valence Electrons – Non-Bonding Electrons – ½ Bonding Electrons For Chlorine, Formal Charge = 7 – 4 – 4/2 = +1 For Oxygen, Formal Charge = 6 – 6 – 2/2 = -1 Here +1 formal charge of the chlorine atom cancels out the -1 formal charge of one of the oxygen atoms. With this, -1 formal charge still remains on another oxygen atom. Therefore the above structure is unstable because there exists another Lewis structure where the formal distribution of some participating atoms is zero. Let us check the correct lewis structure of the ClO2- molecule as below.  

Let us find the formal charge distribution of the above-mentioned molecule. Formal Charge = Valence Electrons – Non-Bonding Electrons – ½ Bonding Electrons For Chlorine, Formal Charge = 7 – 4 – 6/2 = 0 For Oxygen, Formal Charge = 6 – 6 – 2/2 = -1 For Oxygen, Formal Charge = 6 – 4 – 4/2 = 0 This structure is more suitable as the formal charge distribution on two atoms is zero. Studying the formal charge distribution in detail also gives us the reason behind the double bond forming between one oxygen and chlorine atom. Step 4: Find the type of bond formation taking place in one chlorine oxide. One single bond is formed between chlorine and oxygen atoms and a double bond is formed between chlorine and another oxygen atom. The explanation for the same lies in the formal charge distribution that compels the formation of a double bond and a single bond. Even though the new structure is stable, it is the oxygen atom that usually undergoes bond formation with another nearby atom. Step 5: Find the central atom. Chlorine is the central atom because it is present as the single entity within the chlorine dioxide molecule. Moreover, the atom with the lowest electronegativity value becomes the central atom as it has to make the maximum number of bonds. As a result, chlorine becomes the central atom.  

Molecular Geometry of Chlorine Dioxide

From the Lewis structure, it is clear that chlorine dioxide or chlorite ion is a triatomic molecule that is bent in shape. It is bent because of the lone pairs of valence electrons on the chlorine atom and the uneven bond type between each chlorine and oxygen atom. This can be studied in the detail with the help of the Valence Shell Electron Pair Repulsion (VSEPR) Theory or the AXN method. According to this theory, the presence of two lone pairs of valence electrons on the chlorine atom exerts force and bends the structure giving the bond angle slightly lesser than 109°.   We know that a single bond consists of only one sigma bond whereas the double consists of one sigma and one pi bond. Irrespective of the sigma bond considered as the strongest type of bond, the oxygen atom attached to chlorine with a single bond (sigma bond) only bonds with nearby atoms. It is because the double bond formed between chlorine and oxygen atoms is stable and takes a lot of energy to reach the excited state. Here, it is important to know that the valence electron present as the (-) sign on the oxygen atom is responsible for the bond formation because it is unstable and needs more valence electrons to achieve a stable configuration. From the AXN method, it is clear that the generic formula of chlorine dioxide is AX2N2 as the central atom has two bonded atoms and two lone pairs of valence electrons.  Hence the molecular geometry of chlorine dioxide is bent and electron geometry is tetrahedral. Moreover, it might interest you that through the AXN method, we can determine the hybridization of the central atom which is Sp3 in chlorine dioxide.  

Hybridization in Chlorine Dioxide (ClO2)

 

From the AXN method, it is clear that the hybridization of chlorine is sp3. Here it is important to understand that in the case of one more Lewis structure where chlorine and both oxygen atoms are forming double bonds, the hybridization of the chlorine atom will be sp2. Such a Lewis structure is not a usual case because chlorine dioxide is present in ClO2- form. In the case of the chlorite ion, mixing and inter-mixing of one 2s and three 2p orbitals takes place to form four new hybrid orbitals of similar energy. For the sigma bond, head-on overlapping takes place whereas, for the pi bond, lateral overlapping takes place. Sigma bond is more stable than the pi bond because it undergoes head-on overlapping which is much stronger than lateral overlapping of pi bond.  

Polarity in Chlorine Dioxide (ClO2)

Chlorine dioxide is a polar molecule because it is a strong anion and exists in the ionic form. It is important to understand that the rule of electronegativity difference will not be applicable in this case. Although the electronegativity difference between oxygen and chlorine atoms is less than 0.4, chlorine dioxide is a polar molecule which is due to the fact that it is a strong anion. Let us also check out its properties and uses.    

Properties of Chlorine Dioxide (ClO2)

 

Uses of Chlorine Dioxide

  1. It is used during food processing to preserve it for a longer duration.
  2. It is used to eradicate molds.
  3. It is used to control odor.
  4. It is used by healthcare professionals during various dental applications.
  5. It is used as a disinfectant for vehicles, floor, air, swimming pool.
  6. It is used to clean wounds.
  7. It is a strong bleaching agent.  

Conclusion

  1. Chlorine dioxide is a strong anion and mainly exists as chlorite in the ionic form.
  2. The molecular geometry of chlorine dioxide is bent and the bond angle is slightly less than 109 degrees.
  3. The hybridization of chlorine dioxide is sp2 and its ion is sp3.
  4. The hybridization can further be studied in detail with the help of a molecular orbital diagram.
  5. The formal charge distribution on chlorine dioxide is -1.
  6. The hybridization can be studied in the detail with the help of Valence Bond Theory (VBT).
  7. Chlorine dioxide is a polar molecule as it is a strong oxidizing agent.

ClO2 Lewis Structure Geometry Hybridization and Polarity - 55ClO2 Lewis Structure Geometry Hybridization and Polarity - 72ClO2 Lewis Structure Geometry Hybridization and Polarity - 43ClO2 Lewis Structure Geometry Hybridization and Polarity - 11ClO2 Lewis Structure Geometry Hybridization and Polarity - 67