The \(\mathrm{SF}_{5}^{-}\) ion is formed when \(\mathrm{SF}_{4}(g)\) reacts with fluoride salts containing large cations, such as \(\mathrm{CsF}(s)\). Draw the Lewis structures for \(\mathrm{SF}_{4}\) and \(\mathrm{SF}_{5}^{-}\), and predict the molecular structure of each.

We need to find the total number of valence electrons for SF4 and SF5-. We do this by identifying the number of valence electrons each atom brings to the molecule, then add them together. For SF4: - Sulfur has 6 valence electrons. - Each fluorine atom has 7 valence electrons, so we have a total of 4 x 7 = 28 valence electrons from fluorine. Adding the valence electrons together: 6 (S) + 28 (F) = 34 valence electrons For SF5-: - Sulfur has 6 valence electrons. - Each fluorine atom has 7 valence electrons, so we have a total of 5 x 7 = 35 valence electrons from fluorine. - Since it is a negatively charged ion, we add an extra electron to the total count: 35 (F) + 1 = 36 valence electrons. Adding the valence electrons together: 6 (S) + 36 (F) = 42 valence electrons

To draw the Lewis structures, we start by connecting the central atom (Sulfur in both cases) to the surrounding atoms (Fluorine) by single bonds. Then we fill the remaining electron pairs on the surrounding atoms to satisfy the octet rule. Finally, we can assign any leftover electrons as lone pairs on the central atom. For SF4: 1. Connect Sulfur to each of the 4 Fluorine atoms using single bonds. We have used 4 * 2 = 8 electrons so far. 2. Complete the octets of each Fluorine atom. We have used another 24 electrons here (4 * 6 = 24). 3. Assign the remaining 2 electrons as a lone pair on the central Sulfur atom. The Lewis structure of SF4 is completed. For SF5-: 1. Connect Sulfur to each of the 5 Fluorine atoms using single bonds. We have used 5 * 2 = 10 electrons so far. 2. Complete the octets of each Fluorine atom. We have used another 30 electrons here (5 * 6 = 30). 3. Assign the remaining 2 electrons as a lone pair on the central Sulfur atom. The Lewis structure of SF5- is completed.

To predict the molecular structure, we must identify the arrangement of atoms and electron pairs around the central atom. For this, we can use the VSEPR (Valence Shell Electron Pair Repulsion) theory, which states that electron pairs around the central atom repel each other and try to be as far apart as possible. For SF4: There are 4 bonded pairs and 1 lone pair around the central Sulfur atom. This results in a see-saw molecular structure. For SF5-: There are 5 bonded pairs and 1 lone pair around the central Sulfur atom. This results in a square pyramidal molecular structure. In conclusion, SF4 has a see-saw molecular structure, while SF5- has a square pyramidal molecular structure.