The Elements of Group 16 (6A, VI, VIA) The Oxygen Group (Chalcogens ) O, S, Se, Te, Po Valence electron configuration: ns 2np 4 Group 16: The Oxygen Family S and O are clearly nonmetallic in behavior Similar compounds: H2S and H 2O CS 2 and CO 2 SCl 2 and Cl 2O Important differences: Due to properties and characteristics of O. Small size, high electronegativity and inability to employ an expanded valence shell. Hydrogen bonding in water but not in H 2S. OS (O) -2, -1 and 0, but OS(S) -2 to +6 inclusive. 1 Occurrence, Production, and Uses Oxygen is the most abundant element in the earth’s crust (45.5%) and seawater (90%). In the atmosphere, it is second only to N 2 (23.25% by mass). The fractional distillation of liquid air – a simplified representation Oxygen: Molecular Structure Allotropy of Oxygen: Ozone O 3 Lewis Molecular Orbital Theory ΔΔΔ OO 3 O 2(g) 2 O 3(g) H = +285 kJ m.p. O 2 = -218°C m.p. O 3 = -193°C b.p. O 2 = -183°C b.p. O 3 = -112°C O3 is a strong oxidizing agent, more reactive than O 2 + - O3 + 2 H + 2e O2 + H 2O E° = +2.07 V paramagnetic : 2 unpaired - Water purification electrons per molecule 2 Ozone: Structure and Bonding Good Ozone, Bad Ozone The Frasch Process Sulfur is the16 th most abundant element in the crust (0.0384%). Element found as underground deposits, also produced from processes cleaning ‘sour’ natural gas and thermal generating station emissions. Main use is conversion to sulfuric acid . Also used in rubber vulcanization and for dusting some agricultural crops. 3 Allotropy and Polymorphism of Sulfur Sources and Uses of Sulfur and its Oxides Some molecular forms of sulfur Several macroscopic forms of sulfur Selenium and Tellurium Hydrides of Group 16 Similar to sulfur but are more metallic . H2O universal solvent, weak acid, moderate Selenium used in rectifiers and (older) photocopiers. nucleophile H2O2 hydrogen peroxide - strong oxidizing agent (O has OS = -1) Polonium - major uses include bleaching, water treatment A rare radioactive metal. H2S hydrogen sulfide - gas at room temperature - stronger acid than H 2O 4 Hydrides of Group 16 Oxides of Sulfur ∆∆∆ Hydride b.p. Ka1 (aq) Hf(kJ/mol) °°° -14 H2O 100 C 10 -242 (gas) °°° -7 H2S -61 C 10 -20 °°° -4 H2Se -42 C 10 +86 °°° -3 H2Te -2 10 +154 Sulfuric Acid SO 2 Emissions and the Environment →→→ SO 3(g) + H 2SO 4(l) H2S2O7(l) ( oleum ) Smelters and coal-fired power plants are the main →→→ H2S2O7(l) + H 2O( l) 2 H2SO 4(l) source of SO 2. SO 2 is converted to SO 3, which reacts with H 2O to H 0 produce H SO . →→→2 2 4 H2SO 4(l) H2SO 4(aq) Acid rain. Dilute H 2SO 4 A diprotic acid. Levels of SO 2 and H 2SO 4 above 0.10 ppm are considered potentially harmful. Concentrated H 2SO 4 High affinity for water, drying agent 5 Some Oxoanions of Sulfur 6.