SOCl2 (thionyl chloride) has one sulfur atom, one oxygen atom, and two chlorine atoms. In the lewis structure of SOCl2, there are two single bonds and one double bond around the sulfur atom, with two chlorine atoms and one oxygen atom attached to it. Each chlorine atom has three lone pairs, the oxygen atom has two lone pairs, and the sulfur atom has one lone pair.
Here’s how you can draw the SOCl2 lewis structure step by step.
Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: minimize charges again (if there are)
Let’s break down each step in detail.
#1 Draw Sketch
- First, determine the total number of valence electrons
Hence, both sulfur and oxygen have six valence electrons, and chlorine has seven valence electrons.
Since SOCl2 has one sulfur atom, one oxygen atom, and two chlorine atoms, so…
Valence electrons of one sulfur atom = 6 × 1 = 6
Valence electrons of one oxygen atom = 6 × 1 = 6
Valence electrons of two chlorine atoms = 7 × 2 = 14
And the total valence electrons = 6 + 6 + 14 = 26
- Second, find the total electron pairs
We have a total of 26 valence electrons. And when we divide this value by two, we get the value of total electron pairs.
Total electron pairs = total valence electrons ÷ 2
So the total electron pairs = 26 ÷ 2 = 13
- Third, determine the central atom
We have to place the least electronegative atom at the center.
Since sulfur is less electronegative than oxygen and chlorine, assume that the central atom is sulfur.
Therefore, place sulfur in the center and oxygen and chlorine on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 13 electron pairs. And three bonds are already marked. So we have to only mark the remaining ten electron pairs as lone pairs on the sketch.
Also remember that both (sulfur and chlorine) are the period 3 elements, so they can keep more than 8 electrons in their last shell. And oxygen is a period 2 element, so it can not keep more than 8 electrons in its last shell.
Always start to mark the lone pairs from outside atoms. Here, the outside atoms are oxygen and chlorines.
So for oxygen and each chlorine, there are three lone pairs, and for sulfur, there is one lone pair.
Mark the lone pairs on the sketch as follows:
#3 Mark Charges
Use the following formula to calculate the formal charges on atoms:
Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons
For sulfur atom, formal charge = 6 – 2 – ½ (6) = +1
For oxygen atom, formal charge = 6 – 6 – ½ (2) = -1
For each chlorine atom, formal charge = 7 – 6 – ½ (2) = 0
Here, both sulfur and oxygen atoms have charges, so mark them on the sketch as follows:
The above structure is not a stable lewis structure because both sulfur and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.
#4 Minimize Charges
Convert a lone pair of the oxygen atom to make a new S — O bond with the sulfur atom as follows:
In the above structure, you can see that the central atom (sulfur) forms an octet. Hence, the octet rule is satisfied.
Also, the above structure is more stable than the previous structures. Therefore, this structure is the stable lewis structure of SOCl2.
Next: POCl3 Lewis Structure