Hypochlorous acid (HOCl) Lewis structure, molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polar or nonpolar
HOCl is the chemical formula for hypochlorous acid, less commonly known as hydrogen hypochlorite or chlorine hydroxide. It is an oxyacid of chlorine. Most commonly used as a chlorinating agent, an oxidizing agent, in the preparation of cosmetics, disinfectants, etc.
In this article, we will discuss everything related to HOCl chemistry, 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 for all this insightful information, continue reading and satisfying the curiosity of your inborn chemist.
The Lewis structure of hypochlorous acid (HOCl) consists of an oxygen (O) atom at the center. It is bonded to a hydrogen (H) atom on one side and a chlorine (Cl) atom on the other side. There are 2 lone pairs of electrons also present on the central O-atom in the HOCl Lewis structure.
In this way, there are a total of 4 electron density regions or electron domains around the central O-atom in the HOCl Lewis dot structure.
If you want to learn how to draw this Lewis structure, then follow the simple steps given below.
As there are atoms from three different elements of the Periodic Table in HOCl, so you need to look for the position of these elements in the Periodic Table.
Oxygen (O) belongs to Group VI A (or 16), so it has a total of 6 valence electrons. Chlorine (Cl) is a halogen present in Group VII A (or 17); hence it has 7 valence electrons, while hydrogen (H) lies at the top of the Periodic Table containing a single valence electron only.
∴ The HOCl molecule consists of 1 H-atom, 1 O-atom, and 1 Cl-atom. Therefore, the total valence electrons available for drawing the Lewis dot structure of HOCl = 1(1) + 1(6) + 1(7) = 14 valence electrons.
2. Choose the central atom
In this second step, usually the least electronegative atom out of all the concerned atoms is chosen as the central atom.
This is because the least electronegative atom is the one that is most likely to share its electrons with the atoms spread around it.
However, HOCl is an exception.
It has three different elemental atoms present in it. It should be noted that the hydrogen (H) atom can accommodate only 2 electrons in its valence shell so it can form a bond with a single adjacent atom only. This denotes that H cannot be chosen as the central atom.
Oxygen (O) must always form 2 covalent bonds in order to fulfill the octet rule. Chlorine (Cl) is deficient in 1 valence electron only, so it forms a single bond with the adjacent atom.
Keeping all the above factors in mind, even though the Cl-atom is less electronegative than the O-atom, still, the O-atom is selected as a central atom in the HOCl Lewis structure, while the H and Cl-atoms are placed as outer atoms, as shown below.
3. Connect outer atoms with the central atom
Now we need to connect the outer atoms with the central atom of the Lewis structure using single straight lines.
As one hydrogen and one chlorine atom are the outer atoms in the Lewis structure of hypochlorous acid, so both H-atom and the Cl-atom are joined to the central C-atom using straight lines.
Each straight line represents a single covalent bond, i.e., a bond pair containing 2 electrons. There are a total of 2 single bonds in the above diagram.
As 2(2) = 4, that means 4 valence electrons are already consumed out of the 14 initially available.
4. Complete the duplet and/or octet of the outer atoms
As we already identified, the hydrogen and chlorine atoms are the outer atoms in the Lewis dot structure of HOCl.
Each hydrogen (H) atom requires a total of 2 valence electrons in order to achieve a stable duplet electronic configuration.
An O-H single bond already represents 2 valence electrons around the H-atom. This means the H-atom already has a complete duplet in the Lewis structure drawn till yet. Thus, we do not need to make any changes with regard to the hydrogen atom in this structure.
In contrast, a Cl-atom needs a total of 8 valence electrons in order to achieve a stable octet electronic configuration. An O-Cl bond represents 2 electrons which denote that the Cl-atom needs 6 more electrons to complete its octet.
Consequently, 6 valence electrons are placed as 3 lone pairs on the Cl-atom in the HOCl Lewis structure, as shown below.
5. Complete the octet of the central atom
Total valence electrons used till step 4 = 2 single bonds + electrons placed around the Cl-atom, shown as dots = 2(2) + 6 = 10 valence electrons.
Total valence electrons – electrons used till step 4 = 14 – 10 = 4 valence electrons.
These 4 valence electrons are placed as 2 lone pairs on the central O-atom in the HOCl Lewis structure.
2 single bonds and 2 lone pairs of electrons make a total of 8 valence electrons around the central O-atom hence a complete octet electronic configuration.
As a final step, we must check the stability of the Lewis structure obtained in this step. Let us do that using the formal charge concept.
6. Check the stability of Lewis’s structure using the formal charge concept
The fewer formal charges present on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
The absence of any formal charge on all the bonded atoms in the HOCl Lewis structure marks the incredible stability of this structure.
Now that we have obtained the correct and best Lewis representation of hypochlorous acid (HOCl), let us move ahead and discuss its electron geometry and molecular geometry or shape.
What are the electron and molecular geometry of HOCl?
The molecular geometry or shape of hypochlorous acid (HOCl) is bent or V-shaped. However, its ideal electron pair geometry is tetrahedral. 2 lone pairs of electrons present on the central O-atom in the HOCl lead to lone pair-lone pair and lone pair-bond pair electronic repulsions in the molecule.
Thus it adopts a shape different from its ideal electron pair geometry.
Molecular geometry of HOCl
The molecular geometry or shape of HOCl is bent, angular, or V-shaped. There are two lone pairs of electrons present on the central O-atom that leads to strong lone pair-lone pair and lone pair-bond pair repulsions in addition to an H-O and O-Cl bond pair-bond pair repulsive effect.
It is due to the strong repulsive effect, that the H-O and O-Cl bonds tilt inwards, away from the central O-atom. The molecule (HOCl) thus adopts a bent or V-shape, as shown in the figure below. The bonded atoms lie at the vertices of the inverted V-shape.
Always keep in mind that the molecular geometry or shape of a molecule differs based on the different number of lone pairs and bond pairs present around the central atom.
However, its ideal electron pair geometry only depends upon the total number of electron density regions or electron domains around the central atom.
Let’s see how this concept applies to the HOCl molecule.
Electron geometry of HOCl
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 4 electron density regions around the central atom is tetrahedral.
In HOCl, there are 2 single bonds (H-O and O-Cl) and 2 lone pairs around the central oxygen atom, which makes a total of 2 + 2 = 4 electron density regions. Thus, its ideal electron pair geometry is tetrahedral.
A shortcut to finding the electron and the molecular geometry of a molecule is by using 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 shape and geometry of a molecule based on the VSEPR concept.
AXN notation for HOCl molecule
A in the AXN formula represents the central atom. In the HOCl molecule, an oxygen (O) atom is present at the center, so A = O.
X denotes the atoms bonded to the central atom. In HOCl, one hydrogen (H) and one chlorine (Cl) atom are bonded to the central oxygen atom, so X = 1 + 1= 2.
N stands for the lone pairs present on the central atom. As per the Lewis structure of HOCl, there are 2 lone pairs of electrons on the central oxygen, so N = 2.
As a result, the AXN generic formula for HOCl is AX2N2.
Now, you may have a look at the VSEPR chart given below.
The VSEPR chart confirms that the molecular geometry or shape of a molecule with an AX2N2 generic formula is bent or V-shaped, while its ideal electron pair geometry is tetrahedral, as we already recorded for hypochlorous acid (HOCl).
Hybridization of HOCl
The central oxygen (O) atom is sp3 hybridized in the HOCl molecule.
The electronic configuration of oxygen is 1s22s22p4.
During chemical bonding, the 2s atomic orbital of oxygen hybridizes with its three 2p orbitals to yield four sp3 hybrid orbitals.
Each sp3 hybrid orbital of oxygen possesses a 25% s-character and a 75% p-character. However, these four sp3 hybrid orbitals are not equivalent.
Two sp3 hybrid orbitals contain paired electrons which are situated as 2 lone pairs on the central O-atom in HOCl. Contrarily, the other two sp3 hybrid orbitals contain a single electron each which they use for H-O and O-Cl sigma (σ) bond formation on each side of the molecule.
Refer to the figure drawn below.
Another shortcut to finding the hybridization present in a molecule is by using its steric number against the table given below. The steric number of central O-atom in HOCl is 4, so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The HOCl bond angle
The ideal bond angle in a symmetrical tetrahedral molecule is 109.5°. The lone pair-bond pair repulsions in HOCl distort the shape and geometry of the molecule. The H-O-Cl bond angle decreases to about 103.3°. The H-O bond length is 97 pm, while the O-Cl bond length is 169.3 pm respectively.
The H-O bond is stronger and thus shorter in length due to a small electronegativity difference between a hydrogen and an oxygen atom. Contrarily, the O-Cl bond is weaker and thus longer in length as Cl strongly attracts the shared electron cloud from the O-Cl bond to one side.
Pauling’s electronegativity scale states that a covalent chemical bond is polar if the bonded atoms have an electronegativity difference between 0.5 to 1.6 units.
A high electronegativity difference of 1.24 units exists between the bonded hydrogen (E.N = 2.20) and oxygen (E.N = 3.44) atoms in the H-O bond in HOCl.
Similarly, an electronegativity difference of 0.28 units exists between the bonded oxygen and chlorine (E.N = 3.16) atoms in the O-Cl bond. Therefore, the H-O bond is strongly polar, while the O-Cl bond is weakly polar.
Oxygen being more electronegative than the H and Cl-atoms, attracts the shared electron cloud from both the H-O and O-Cl single covalent bonds.
Thus, the central O-atom gains a partial negative (δ–) charge, the Cl-atom obtains a partial positive (δ+) charge, while the H-atom attains a double partial positive (δ++) charge to represent extreme electron deficiency.
In short, the electron cloud stays non-uniformly spread over the molecule. The bent shape of HOCl further endorses the polarity effect. The dipole moments of individually polar H-O and O-Cl bonds do not get cancelled equally. Consequently, HOCl is a polar molecule overall (net µ = 1.57 D).
The HOCl Lewis structure displays a total of 14 valence electrons, i.e., 14/2 = 7 electron
Out of the 7 electron pairs, there are 2 bond pairs and 5 lone pairs of electrons.
The 2 bond pairs comprise an H-O bond and an O-Cl single covalent bond.
The 5 lone pairs include 3 lone pairs on the outer Cl-atom and 2 lone pairs on the central O-atom.
What is the molecular geometry or shape of HOCl?
The molecular geometry or shape of HOCl is bent, angular, or V-shaped. An O-atom at the center is bonded to an H-atom and a Cl-atom, one on each side. It also consists of 2 lone pairs of electrons.
Lone pair-lone pair and lone pair-bond pair repulsions tilt the bond pairs away from the center and towards each other. Thus, HOCl adopts a bent shape, different from its ideal electron pair geometry, i.e., tetrahedral.
How is the shape of a perchlorate [ClO4]– ion different from that of hypochlorous acid (HOCl)?
The bonded atoms lie along the four vertices of a tetrahedron and the central O-atom has no lone pair of electrons. Thus there is no distortion in its shape or geometry.
HOCl has a bent shape. Two lone pairs on the central O-atom distort its shape and geometry.
What is the overall charge present on HOCl?
Zero formal charges present on all three bonded atoms in the HOCl Lewis structure means there is no formal charge present on the HOCl molecule overall.
The total number of valence electrons available for drawing hypochlorous acid (HOCl) Lewis structure is 14.
The molecular geometry or shape of HOCl is bent, angular, or V-shaped.
The ideal electronic geometry of HOCl is tetrahedral.
The central O-atom has sp3 hybridization in the HOCl molecule.
The bonded atoms form a mutual bond angle of 103.3° in HOCl.
The H-O bond length is 97 pm, while the O-Cl bond length is 169.3 pm.
HOCl is an extremely polar molecule (net µ= 1.57 D).
Zero formal charges present on all the bonded atoms in the HOCl molecule account for the extraordinary stability of the Lewis structure drawn in this article.
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.
