SiS2 Lewis structure

SiS₂ (silicon disulfide) has one silicon atom and two sulfur atoms.

In the SiS₂ Lewis structure, there are two double bonds around the silicon atom, with two sulfur atoms attached to it, and on each sulfur atom, there are two lone pairs.

Alternative method: Lewis structure of SiS₂

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, silicon lies in group 14, and sulfur lies in group 16.

Hence, silicon has four valence electrons and sulfur has six valence electrons.

Since SiS₂ has one silicon atom and two sulfur atoms, so…

Valence electrons of one silicon atom = 4 × 1 = 4
Valence electrons of two sulfur atoms = 6 × 2 = 12

And the total valence electrons = 4 + 12 = 16

Learn how to find: Silicon valence electrons and Sulfur valence electrons

• Second, find the total electron pairs

We have a total of 16 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 = 16 ÷ 2 = 8

• Third, determine the central atom

We have to place the least electronegative atom at the center.

Since silicon is less electronegative than sulfur, assume that the central atom is silicon.

Therefore, place silicon in the center and sulfurs on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 8 electron pairs. And two Si — S bonds are already marked. So we have to only mark the remaining six electron pairs as lone pairs on the sketch.

Also remember that both (silicon and sulfur) are the period 3 elements, so they can keep more than 8 electrons in their 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 silicon, there is zero lone pair because all six electron pairs are over.

Mark the lone pairs on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For silicon atom, formal charge = 4 – 0 – ½ (4) = +2

For each sulfur atom, formal charge = 6 – 6 – ½ (2) = -1

Here, both silicon and sulfur atoms have charges, so mark them on the sketch as follows:

The above structure is not a stable Lewis structure because both silicon and sulfur atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

Convert a lone pair of the sulfur atom to make a new Si — S bond with the silicon atom as follows:

Since there are charges on silicon and sulfur atoms, again convert a lone pair of the sulfur atom to make a new Si — S bond with the silicon atom as follows:

Final structure

The final structure of SiS₂ features a central silicon atom linked to two sulfur atoms through double covalent bonds. In this arrangement, the silicon atom satisfies the octet rule by forming four total bonds, while each sulfur atom fulfills its octet by retaining two lone pairs alongside its double shared bond. Within this layout, all atoms achieve a complete valence shell without the need for an expanded octet. This configuration represents the most stable state for the molecule because it results in a formal charge of zero for every atom involved. Accordingly, this specific electronic distribution serves as the definitive and most accurate Lewis representation of silicon disulfide.

Next: COF₂ Lewis structure

External links

• https://geometryofmolecules.com/sis2-lewis-structure-hybridization-molecular-geometry-bond-angles/
• https://techiescientist.com/sis2-lewis-structure/
• https://lambdageeks.com/sis2-lewis-structure/
• https://oneclass.com/homework-help/chemistry/7030403-sis2-lewis-structure.en.html