O-Level Chemical Bonding and Structure: worked solution

Question

In its compounds sulfur can hold up to 12 electrons in its outer shell; two such compounds are sulfuryl fluoride (SO2F2) and sodium pyrosulfate (Na2S2O7). In sulfuryl fluoride a central S atom is double bonded to two O atoms (O=S=O) and single bonded to one F above and one F below the sulfur. (a) Draw a dot-and-cross diagram of sulfuryl fluoride showing only the valence electrons.

Sulfuryl fluoride SO2F2: central S has 6 valence electrons. It forms two S=O double bonds and two S-F single bonds. Total bonding electrons around S = 2 double bonds (4 pairs) + 2 single bonds (2 pairs) = 12 electrons (6 bonding pairs), consistent with the expanded octet stated. Dot-and-cross diagram (valence electrons only): - S in the centre with no lone pairs. - Each O joined by a double bond (two shared pairs, shown as two dots + two crosses). Each doubly-bonded O carries two lone pairs (4 electrons) to complete its octet. - Each F joined by a single bond (one shared pair). Each F carries three lone pairs (6 electrons) to complete its octet. So: O=S=O in a horizontal plane, one F above S and one F below S, each bond drawn with the correct number of shared electrons (one dot from S, one cross from the other atom per shared electron), lone pairs on each O and each F.