Lewis structure of SF3+

SF₃⁺ (sulfur trifluoride) has one sulfur atom and three fluorine atoms.

In the Lewis structure of SF₃⁺, there are three single bonds around the sulfur atom, with three fluorine atoms attached to it. Each fluorine atom has three lone pairs, and the sulfur atom has one lone pair.

Also, there is a positive (+1) charge on the sulfur atom.

Alternative method: SF₃⁺ Lewis structure

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, sulfur lies in group 16, and fluorine lies in group 17.

Hence, sulfur has six valence electrons and fluorine has seven valence electrons.

Since SF₃⁺ has one sulfur atom and three fluorine atoms, so…

Valence electrons of one sulfur atom = 6 × 1 = 6
Valence electrons of three fluorine atoms = 7 × 3 = 21

Now the SF₃⁺ has a positive (+1) charge, so we have to subtract one electron.

So the total valence electrons = 6 + 21 – 1 = 26

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

• 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 fluorine, assume that the central atom is sulfur.

Therefore, place sulfur in the center and fluorines on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 13 electron pairs. And three S — F bonds are already marked. So we have to only mark the remaining ten electron pairs as lone pairs on the sketch.

Also remember that sulfur is a period 3 element, so it can keep more than 8 electrons in its last shell. And fluorine 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 fluorines.

So for each fluorine, there are three lone pairs, and for sulfur, there is one lone pair.

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 sulfur atom, formal charge = 6 – 2 – ½ (6) = +1

For each fluorine atom, formal charge = 7 – 6 – ½ (2) = 0

Here, the sulfur atom has a charge, so mark it on the sketch as follows:

Final structure

The final structure of SF₃⁺ contains a central sulfur atom linked to three fluorine atoms through single covalent bonds. In this configuration, the sulfur atom satisfies the octet rule by forming three bonds and retaining one lone pair, while each of the three fluorine atoms fulfills its octet by maintaining three lone pairs alongside its single shared bond. Within this layout, the sulfur atom possesses a positive formal charge, which is consistent with the overall charge of the cation. This arrangement represents the most stable state for the ion because it allows all atoms to achieve complete octets while minimizing the distribution of formal charges. Accordingly, this specific electronic distribution serves as the definitive and most accurate Lewis representation of the sulfur trifluoride cation.

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 fewer electron than the valence count of the neutral atoms.

Next: HOCN Lewis structure

External video

• How to Draw the Lewis Dot Structure for SF3 + – YouTube • Wayne Breslyn