Draw the Lewis structure of SF5+. (a) What is the total number of electron pairs in the Lewis structure? (b)What is the number of nonbonding electron pairs on the central atom? (c) What is the geometry of the electron pairs around the central atom? (d) What is the geometry of the molecule?
The Correct Answer and Explanation is:
Here are the answers and explanation for the SF₅⁺ cation.
The Lewis structure for SF₅⁺ has Sulfur as the central atom single bonded to five Fluorine atoms. Each Fluorine atom has three lone pairs of electrons. The overall structure has a positive one charge, which is located on the central Sulfur atom.
(a) The total number of electron pairs is 20.
(b) The number of nonbonding electron pairs on the central atom is 0.
(c) The geometry of the electron pairs around the central atom is trigonal bipyramidal.
(d) The geometry of the molecule is trigonal bipyramidal.
To determine the properties of the sulfur pentafluoride cation, SF₅⁺, we first construct its Lewis structure. We begin by calculating the total number of valence electrons. Sulfur, in Group 16, contributes 6 valence electrons. Each of the five fluorine atoms, from Group 17, contributes 7 valence electrons, for a total of 35 from fluorine. Because the ion has a positive one charge, we subtract one electron from the total count. This gives a total of 6 + (5 * 7) – 1 = 40 valence electrons. This total of 40 electrons corresponds to 20 electron pairs, which answers question (a).
Next, we arrange the atoms. Sulfur is less electronegative than fluorine, so it serves as the central atom, bonded to the five fluorine atoms. Creating five single bonds uses 10 electrons (5 pairs). The remaining 30 electrons (15 pairs) are distributed as nonbonding lone pairs around the five terminal fluorine atoms, with each fluorine receiving 6 electrons (3 pairs) to satisfy its octet.
The central sulfur atom is now bonded to five other atoms and has no remaining electrons to form lone pairs. Therefore, the number of nonbonding electron pairs on the central sulfur atom is zero, answering question (b).
To determine the geometries, we apply VSEPR theory. The geometry of the electron pairs is based on the total number of electron domains around the central atom. The sulfur atom has five electron domains, all of which are bonding pairs from the S-F bonds. According to VSEPR theory, five electron domains will arrange themselves in a trigonal bipyramidal geometry to minimize repulsion. This answers question (c).
The geometry of the molecule describes the arrangement of the atoms. Since there are no nonbonding electron pairs on the central sulfur atom, the molecular geometry is identical to the electron pair geometry. Thus, the molecular geometry of SF₅⁺ is also trigonal bipyramidal, answering question
