Thionyl chloride (SOCl2) lewis dot structure, molecular geometry, polar or non polar, Bond angle
Thionyl chloride appears as a colourless liquid is an inorganic compound with the chemical formula SOCl2. It has a suffocating pungent odour and is primarily used as a chlorinating agent. It is highly corrosive and toxic in nature.
In this article, we will discuss SOCl2 lewis structure, molecular geometry, bond angle, hybridization, polar or nonpolar, etc.
Thionyl chloride is used in the production of chemical weapons due to its high toxicity nature. Long term inhalation of this compound can cause many adverse health effects.
Properties of Thionyl chloride
It appears as colourless to yellow fuming liquid
It is soluble in water.
It has a boiling point of 74.6 °C and a melting point of −104.5 °C.
SOCl2 lewis structure contains a sulfur atom (S) in the central position whereas the two chlorine (Cl) and one oxygen atom (O) spread evenly around it. There is one double bond and two single bonds present in the lewis structure of SOCl2.
The lewis dot structure of SOCl2 disobeys the octet rule for attaining stability, let’s see how to draw this in a simple way.
Steps to draw lewis structure of SOCl2
1. Count total valence electron in SOCl2
In the very first step, we will count the total valence electron in the SOCl2 molecule. To find the valence electron, look at the periodic group of the individual atoms – sulfur, oxygen, and chlorine.
The chlorine atom belongs to the periodic group 7A or 17th in the periodic table, hence, the valence electron in the chlorine atom is 7. The oxygen and sulfur atom are situated in the same periodic group which is 6A or 16th in the periodic table.
Hence, the valence electron in both sulfur and oxygen is 6.
∴ Total valence electron available for drawing the Lewis structure of SOCl2 = 6 + 6 + 7(2) = 26 valence electrons [∴SOCl2 has one oxygen, one sulfur and two chlorine atoms]
2. Find the least electronegative atom and place it at center
Now we will find the least electronegative atom in the SOCl2 compound, after that, we will place it at the center in the lewis diagram and the rest atoms will be spread around it.
The electronegativity value of the sulfur atom is 2.58, for a chlorine atom, it is 3.16. And for oxygen atoms, the electronegativity is 3.44.
Hence, the sulfur atom is the least electronegative atom in the SOCl2 compound, therefore, we will put the sulfur atom at a central position in the lewis diagram.
3. Connect outer atoms to central atom with a single bond
In this step, we simply connect each outer atom(chlorine and oxygen) to the central atom(sulfur) with the help of a single bond.
Now count the valence electron used in the above structure. A single bond means two electrons, in the above structure, three single bonds are used for connecting the two chlorine and one oxygen atom to the sulfur central atom.
Therefore, (3 single bonds × 2) = 6 valence electrons are used in the above structure from the total of 26 valence electrons available for drawing the lewis structure of SOCl2.
∴ (26 – 6) = 20 valence electrons
So, we are left with 20 valence electrons more.
4. Place remaining valence electrons starting from outer atom first
In this step, we will put the remaining valence electron on the outer atom first for completing their octet. In a SOCl2 molecule, the outer atom is oxygen and chlorine. And both these require 8 electrons in their outer shell to complete the octet.
As you see in the above figure, we have placed the 6 electrons represented as dots around each outer atom(chlorine and oxygen). This is because chlorine and oxygen atoms already have 2 electrons(one single bond) in their outer shell.
Hence, both these only require 6 more electrons for completing the octet.
Now once again count the total valence electron in the above structure.
∴ (3 single bond × 2 electrons + 18 electrons represented as dots) = 24 valence electrons are used in the above structure.
5. Complete central atom octet and make covalent bond if necessary
As we already completed the octet of outer atoms, now, we have to complete the octet of the central atom also which is sulfur in the SOCl2 compound.
In the 4th step structure, we used the 24 valence electrons from the total of 26 available valence electrons. Hence, we are left with only two valence electrons. Just put these electrons over the sulfur atom.
So, we have used all the valence electrons that are available for drawing the lewis structure of SOCl2. But we don’t know yet if the above structure is stable or not.
For checking this we will move forward to 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 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 sulfur atom-
⇒ Valence electron of sulfur = 6
⇒ Lone pair electrons on sulfur = 2
⇒ Shared pair electrons around sulfur(three single bonds) = 6
∴ F.C. on sulfur atom = (6 – 2 – 6/2) = +1.
For oxygen atom –
⇒ Valence electron of oxygen = 6
⇒ Lone pair electrons on oxygen = 6
⇒ Shared pair electrons around oxygen(one single bond) = 2
∴ F.C. on oxygen atom = (6 – 6 – 2/2) = -1.
For chlorine atom –
⇒ Valence electron of chlorine = 7
⇒ Lone pair electrons on chlorine = 6
⇒ Shared pair electrons around chlorine(one single bond) = 2
∴ F.C. on chlorine atom = (7 – 6 – 2/2) = 0
Obviously, the above 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 lone pairs to bond pairs (covalent bonds).
Note: The sulfur atom is exceptional to the octet rule as it can hold more than 8 electrons in its outermost shell because it is the element of the period (row) 3 in the periodic table that can have expanded octet.
Expanded octet: A case where an atom shares more than eight electrons with its bonding partners.
The chlorine atom already getting the formal charge zero, hence, we must not try to touch it. Just convert the lone pair of oxygen atoms to the bonded pair(covalent bond).
As you see in the above figure, we convert the one lone pairs of oxygen atoms to a covalent bond and we successfully reduced the formal charge of sulfur and oxygen atom equal to zero.
So, the final lewis structure of SOCl2 contains one double bond and two single bonds, the chlorine and oxygen atom have 8 electrons in their outer shell and the sulfur central atom has 10 electrons in its outer shell as it has the ability to expand the octet.
SOCl2 lewis dot structure
∴ The overall formal charge in SOCl2 is zero. Hence, the above lewis structure of thionyl chloride is most stable, appropriate, and reliable.
The molecular geometry of SOCl2 is a trigonal pyramid because the central atom of it has one lone pair and is attached to the three bonded pairs that will repel each other according to the VSEPR theory, hence, this electron cloud (lone pair and bond pair) tried to remain far as much as possible and in this process, they take up the position where the shape of SOCl2 appears as a trigonal pyramid.
SOCl2 molecular geometry
We can use another method for finding the electron and molecular geometry of SOCl2 which is the AXN method.
AXN notation for SOCl2 molecule:
A represents the central atom, so, in the SOCl2 molecule, sulfur is the central atom. A = Sulfur
X denotes the bonded atoms to the central atom, as we know, sulfur is bonded with two chlorine atoms and one oxygen atom. Therefore, X = 3
N denotes the lone pair on the central atom, as per SOCl2 lewis structure, sulfur has only one lone pair. Hence, N = 1
So, the AXN notation for the SOCl2 molecule becomes AX3N1
As per the VSEPR chart, if a molecule central atom is attached with three bonded atoms and has contained only one lone pair on the central atom then the molecular geometry of that molecule is the trigonal pyramid in nature, and electron geometry is tetrahedral.
Bonded atoms
Lone pair
Generic formula
Hybridization
Molecular geometry
Electron geometry
1
0
AX
S
Linear
Linear
2
0
AX2
Sp
Linear
Linear
1
1
AXN
Sp
Linear
Linear
3
0
AX3
Sp²
Trigonal planar
Trigonal planar
2
1
AX2N
Sp²
Bent
Trigonal planar
1
2
AXN2
Sp²
Linear
Trigonal planar
4
0
AX4
Sp³
Tetrahedral
Tetrahedral
3
1
AX3N1
Sp³
Trigonal pyramid
Tetrahedral
2
2
AX2N2
Sp³
Bent
Tetrahedral
1
3
AXN3
Sp³
Linear
Tetrahedral
3
2
AX3N2
Sp³d
T-shaped
Trigonal bipyramidal
Hence, the molecular shape of SOCl2 is a trigonal pyramid, and electron geometry is tetrahedral.
What is the Hybridization of SOCl2?
We can calculate the hybridization of SOCl2 using the steric number formula given below:
∴ Steric number of SOCl2 = (Number of bonded atoms attached to sulfur + Lone pair on sulfur atom)
As per the SOCl2 lewis dot structure, the sulfur atom is bonded with two chlorine atoms and one oxygen atom and contains only one lone pair.
∴ Steric number of SOCl2 = (3 + 1) = 4
So, for the steric number of 4, we get the hybridization of SOCl2 is Sp3.
What is the Bond angle of SOCl2?
The bond angle of ∠O = S – Cl is 107.4º and ∠Cl – S – Cl is = 96.5º.
Thionyl chloride polarity: is SOCl2 polar or nonpolar
So, Is SOCl2 polar or nonpolar? SOCl2 is a polar molecule because of its asymmetrical structure that causes uneven charge distribution and that contributes to the nonzero dipole moment and making this molecule polar in nature.
Also, the sulfur atom gets the positive charge because of its less electronegativity and both chlorine and oxygen atom gets negative charge because of there high electronegativity.
The separation of positive and negative charges leads the dipole moment in SOCl2 directed from sulfur to chlorine or sulfur to oxygen.
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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