Question

In which of the following molecules does the sulfur have an expanded octet? For those that do, write the Lewis structure. (a) \(\mathrm{SO}_{2}\) (b) \(\mathrm{SF}_{4}\) (c) \(\mathrm{SO}_{2} \mathrm{Cl}_{2}\) (d) \(\mathrm{SF}_{6}\)

Short answer

Answer: The molecules with sulfur having an expanded octet are (b) SF₄, (c) SO₂Cl₂, and (d) SF₆. Their Lewis structures are as follows: (b) SF₄ Lewis structure: F | F-S-F | F (c) SO₂Cl₂ Lewis structure: O || Cl-S-O | Cl (d) SF₆ Lewis structure: F | F-S-F-S-F | F

Step-by-step solution

Recall the octet rule

The octet rule states that atoms tend to have a full outer electron shell, consisting of 8 electrons. This can be achieved through forming covalent bonds or gaining/losing electrons.

Identify the central atom and count the valence electrons

In each molecule, sulfur (S) is the central atom. Sulfur belongs to group 16, which means it has 6 valence electrons.

For each molecule, check if sulfur has an expanded octet

(a) \(\mathrm{SO}_{2}\): Sulfur is bonded to two oxygen atoms, forming two double bonds. Since each double bond requires 2 electrons, sulfur uses 4 electrons to bond, still keeping with the octet rule and not forming an expanded octet. (b) \(\mathrm{SF}_{4}\): Sulfur is bonded to four fluorine atoms, forming four single bonds. Since each single bond requires 1 electron, sulfur uses 8 electrons to bond, breaking the octet rule and forming an expanded octet. (c) \(\mathrm{SO}_{2} \mathrm{Cl}_{2}\): Sulfur is bonded to two oxygen atoms and two chlorine atoms, forming two double bonds and two single bonds. Since each double bond requires 2 electrons and each single bond requires 1 electron, sulfur uses 10 electrons to bond, breaking the octet rule and forming an expanded octet. (d) \(\mathrm{SF}_{6}\): Sulfur is bonded to six fluorine atoms, forming six single bonds. Since each single bond requires 1 electron, sulfur uses 12 electrons to bond, breaking the octet rule and forming an expanded octet.

Draw Lewis structures for molecules with expanded octets

(b) \(\mathrm{SF}_{4}\) Lewis structure: Sulfur forms 4 single bonds with 4 fluorine atoms and has a lone pair of electrons. Thus, the structure can be drawn as: F | F-S-F | F (c) \(\mathrm{SO}_{2} \mathrm{Cl}_{2}\) Lewis structure: Sulfur forms 2 double bonds with 2 oxygen atoms and 2 single bonds with 2 chlorine atoms. The structure can be drawn as: O || Cl-S-O | Cl (d) \(\mathrm{SF}_{6}\) Lewis structure: Sulfur forms 6 single bonds with 6 fluorine atoms. The structure can be drawn as: F | F-S-F-S-F | F