PS3- Lewis structure

PS₃^– has one phosphorus atom and three sulfur atoms.

In PS₃^– Lewis structure, there is one single bond and two double bonds around the phosphorus atom, with three sulfur atoms attached to it. The sulfur atom with a single bond has three lone pairs, and the sulfur atom with double bonds has two lone pairs.

Also, there is a negative (-1) charge on the sulfur atom with a single bond.

Alternative method: Lewis structure of PS₃^–

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, phosphorus lies in group 15, and sulfur lies in group 16.

Hence, phosphorus has five valence electrons and sulfur has six valence electrons.

Since PS₃^– has one phosphorus atom and three sulfur atoms, so…

Valence electrons of one phosphorus atom = 5 × 1 = 5
Valence electrons of three sulfur atoms = 6 × 3 = 18

Now the PS₃^– has a negative (-1) charge, so we have to add one more electron.

So the total valence electrons = 5 + 18 + 1 = 24

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

• Second, find the total electron pairs

We have a total of 24 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 = 24 ÷ 2 = 12

• Third, determine the central atom

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

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

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

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 12 electron pairs. And three P — S bonds are already marked. So we have to only mark the remaining nine electron pairs as lone pairs on the sketch.

Also remember that both (phosphorus 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 phosphorus, there is zero lone pair because all nine 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 phosphorus atom, formal charge = 5 – 0 – ½ (6) = +2

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

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

The above structure is not a stable Lewis structure because both phosphorus 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 P — S bond with the phosphorus atom as follows:

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

Final structure

The final structure of PS₃^– consists of a central phosphorus atom linked to three sulfur atoms. In this configuration, the phosphorus atom utilizes an expanded valence shell to form two double covalent bonds and one single covalent bond, leaving no lone pairs on the phosphorus. Within this layout, each of the three sulfur atoms satisfies the octet rule: the two double-bonded sulfur atoms maintain two lone pairs each, while the single-bonded sulfur atom retains three lone pairs. This arrangement represents the most stable state for the ion because it minimizes formal charges across the structure, placing the negative formal charge on the sulfur atom, which is more electronegative than phosphorus. Thus, this specific electronic distribution serves as the definitive and most accurate Lewis representation of PS₃^–.

To properly represent this as a polyatomic ion, the entire Lewis structure is enclosed within square brackets. The overall charge of 1- is then written as a superscript outside the brackets at the top right, indicating that the structure possesses one additional electron beyond the valence count of the neutral atoms.

Next: SOF₂ Lewis structure

External video

• PS3- Lewis Structure: How to Draw the Lewis Structure for PS3 -1 – YouTube • Wayne Breslyn

External links

• https://www.chegg.com/homework-help/questions-and-answers/consider-lewis-structure-ps3-ion-right–many-total-electrons-used-construct-structure-ion–q103924829
• https://www.bartleby.com/questions-and-answers/consider-the-molecule-ps3-1.-how-many-effective-pairs-are-around-the-central-atom/f8ed6467-2bcc-4d1c-87db-6c734906c7e1