SeS2 (selenium disulfide) has one selenium atom and two sulfur atoms. In the lewis structure of SeS2, there are two double bonds around the selenium atom, with two sulfur atoms attached to it. Each sulfur atom has two lone pairs, and the selenium atom has one lone pair.
Here’s how you can draw the SeS2 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 selenium and sulfur have six valence electrons.
Since SeS2 has one selenium atom and two sulfur atoms, so…
Valence electrons of one selenium atom = 6 × 1 = 6
Valence electrons of two sulfur atoms = 6 × 2 = 12
And the total valence electrons = 6 + 12 = 18
- Second, find the total electron pairs
We have a total of 18 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 = 18 ÷ 2 = 9
- Third, determine the central atom
We have to place the least electronegative atom at the center.
Since selenium is less electronegative than sulfur, assume that the central atom is selenium.
Therefore, place selenium in the center and sulfurs on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 9 electron pairs. And two Se — S bonds are already marked. So we have to only mark the remaining seven electron pairs as lone pairs on the sketch.
Also remember that selenium is a period 4 element, so it can keep more than 8 electrons in its last shell. And sulfur is a period 3 element, so it can also keep more than 8 electrons in its last shell.
Always start to mark the lone pairs from outside atoms. Here, the outside atoms are sulfurs.
So for each sulfur, there are three lone pairs, and for selenium, 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 selenium atom, formal charge = 6 – 2 – ½ (4) = +2
For each sulfur atom, formal charge = 6 – 6 – ½ (2) = -1
Here, both selenium and sulfur atoms have charges, so mark them on the sketch as follows:
The above structure is not a stable lewis structure because both selenium and sulfur atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.
#4 Minimize Charges
Convert a lone pair of the sulfur atom to make a new Se — S bond with the selenium atom as follows:
#5 Minimize Charges Again
Since there are charges on selenium and sulfur atoms, again convert a lone pair of the sulfur atom to make a new Se — S bond with the selenium atom as follows:
In the above structure, you can see that the central atom (selenium) 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 SeS2.
Next: SeF2 Lewis Structure