Draw Lewis formulas for sulfur difluoride SF2 and sulfur hexafluoride SF6. Is either one an exception to the octet rule?

To draw the Lewis structures for sulfur difluoride (SF₂) and sulfur hexafluoride (SF₆), we start by determining the total number of valence electrons for each molecule.

For SF₂:

• Sulfur (S) has 6 valence electrons.
• Fluorine (F) has 7 valence electrons, and since there are 2 fluorine atoms, that gives us 2 x 7 = 14 valence electrons from fluorine.
• In total, SF₂ has 6 + 14 = 20 valence electrons.

Next, we arrange the atoms with the sulfur atom in the center and the two fluorine atoms on either side. The sulfur atom will form single bonds with each fluorine atom. Each bond will use 2 electrons, so that accounts for 4 electrons (2 for each bond):

Electrons left = 20 – 4 = 16. Each fluorine atom needs 6 more electrons to complete its octet (making a total of 8). We distribute the remaining electrons to the fluorine atoms:

• 2 F atoms x 6 electrons each = 12 electrons.

We have used 4 (from the bonds) + 12 = 16 electrons, leaving us with 0 electrons. The Lewis structure for SF₂ consists of two single bonds to each F atom with 3 lone pairs on each F:

For SF₆:

• Sulfur has 6 valence electrons.
• Each fluorine has 7 valence electrons, and since there are 6 fluorine atoms, that gives us 6 x 7 = 42 valence electrons from fluorine.
• In total, SF₆ has 6 + 42 = 48 valence electrons.

Similarly, sulfur is in the center, bonded to the 6 fluorine atoms. Each bond again uses 2 electrons, so 6 x 2 = 12 electrons for the bonds:

Electrons left = 48 – 12 = 36. Each of the 6 fluorine atoms needs 6 electrons to complete their octets:

• 6 F atoms x 6 electrons each = 36 electrons.

All electrons are used, and each fluorine has 3 lone pairs surrounding it, while sulfur has six single bonds:

Regarding the octet rule:

Sulfur difluoride (SF₂) adheres to the octet rule since the sulfur atom shares its electrons with 2 fluorine atoms, allowing it to complete its octet. However, sulfur hexafluoride (SF₆) is an exception as sulfur can expand its valence shell and accommodate more than 8 electrons due to its position in the third period of the periodic table. This allows it to have 12 electrons in total around it, which gives it stability in the SF₆ configuration.