In SF4 (sulfur tetrafluoride), the sulfur (S) atom forms bonds with four fluorine (F) atoms. To determine the number of lone pairs of electrons on the S atom, we need to consider the total number of valence electrons available for sulfur and the number of electrons involved in bonding.
The electron configuration of sulfur is [Ne] 3s2 3p4, with six valence electrons (2 in the 3s orbital and 4 in the 3p orbital). Each fluorine atom contributes one valence electron, resulting in a total of 6 + 4(7) = 34 valence electrons.
In SF4, each fluorine atom forms a single bond with sulfur, consuming 4 valence electrons (4 bonds × 2 electrons/bond = 8 electrons). So, 4 × 2 = 8 valence electrons are involved in bonding, leaving 34 - 8 = 26 valence electrons remaining.
To distribute these remaining electrons, we first place them around the fluorine atoms as lone pairs. Each fluorine atom requires 2 electrons to complete its octet (except for the central sulfur atom, which can accommodate more than 8 electrons). Distributing 2 electrons around each of the four fluorine atoms accounts for 4 × 2 = 8 electrons.
The remaining 26 - 8 = 18 electrons are placed as lone pairs on the central sulfur atom. Each lone pair consists of two electrons. Therefore, there are 18/2 = 9 lone pairs of electrons on the sulfur (S) atom in SF4.