Chapter 16 Group 16 Elements Physical Properties The elements Halides, oxohalides, oxides, salts of oxoacids Metal sulfides, polysulfides, polyselenides, polytellurides Compounds of sulfur and selenium with nitrogen 1 • Dioxygen makes up 21% of the Earth’s atmosphere and 47% of the Earth’s crust is composed of O-containing compounds (water, limestone, silica, silicates). • Sulfur occurs around volcanoes and hot springs, iron pyrites fool’s gold (FeS 2), and other minerals. • Selenium and Tellurium are relatively rare and occur in only a few minerals • Polonium is omitted because its abundance is only 3 × 10 −7 ppb, giving a negative number on the log scale. Relative abundances of the group 16 elements in the Earth’s crust Production of sulfur in the US from 1980 to 2008 2 Uses of sulfur and sulfuric acid 3 ∆ o Given the fH (Na 2O,s) = -414 kJ/mol, determine the + 2- enthalpy change for the process: 2Na (g) + O (g) Na 2O(s) Hint: Create an appropriate Born-Haber cycle and look up the necessary values for each of the steps. ∆ o 2 aH (Na) 2Na (s) + ½ O 2(g) 2Na (g) + O (g) ∆ o aH (O) ∆ o fH (Na 2O,s) ∆ o 2 IE (Na) EA H 1(O) 1 ∆ o EA H 2(O) ∆ Ho(Na O,s) lattice 2 + 2- Na 2O (s) 2Na (g) + O (g) 4 Chemistry of oxygen MnO 2 or Pt catalyst 2H 2O2 O2 + 2H 2O ∆, MnO 2 catalyst 2KClO 3 3O 2 + 2KCl + - 2- Describe bonding in [O 2] , O 2, [O 2] , [O 2] using MO theory. + - O2 + PtF 6 [O 2] [PtF 6] + - 2O 2F2 + 2BF 3 2[O 2] [BF 4] + F 2 Chemistry of ozone and ozonide ∆ o -1 3/2 O 2(g) → O3(g) fH (O 3,g,298 K) = +142.7 kJ mol + - o O3(g) + 2H (g) + 2e ⇌ O2(g) + H 2O(l) E = +2.07 V − The structures of O 3 and [O 3] , and contributing resonance structures in O 3. − • The O O bond order in O 3 is taken to be 3/2. 2KOH + 5O 3 2KO 3 + 5O 2 + H 2O (Ozonide salts) Phosphite ozonide 5 Sulfur: allotropes S6 S7 S8 catena -S S8 + 24F 2 → 8SF 6 S8 + 4Cl 2 → 4S 2Cl 2 S8 + 4Br 2 → 4S 2Br 2 SF 6 2+ structure of [S 2I4] 6 2- Polysulfides, [S x] , and polythionates are formed from reaction of sulfur with hot aqueous alkali polythionate Vulcanization – soft rubber is toughened by cross-linking polyisoprene chains. Hydrocarbons are dehydrogenated when heated with sulfur and further reaction with alkenes occur. Other reactions of sulfur: - - - 1/8 S 8 + CO O=C=S 1/8 S8 + CN N=C=S ⇌ NΞC-S Na 2SO 3 + 1/8S 8 –H2O, 373 K Na 2S2O3 S8 + 3AsF 5 –liquid SO 2 [S 8][AsF 6]2 + AsF 3 2+ [S 8] is red and undergoes a change in ring conformation… 2+ [S 8] 7 2+ [S 19 ] 2+ S8 • transannular interactions • Cross ring S-S separations smaller than the sum of van der Waals radii • Two 7-membered, puckered rings • Delocalized bonding connected by a 5-atom chain • Charge localized on the three- coordinate S Selenium 4SeCl 2 + 4Ph 3PSe Se 8 + 4Ph 3PCl 2 Inorganic Chemistry By Egon Wiberg, Nils Wiberg, Arnold Frederick Holleman 8 tellurium 4+ 2ReCl 4 + 15Te + TeCl 4 –heat in sealed tube → 2[Te 8][ReCl 6] Production of H 2O2 BaO 2 + H 2SO 4 → BaSO 4 + H2O2 2[NH 4][HSO 4] – electrolytic oxidation, “-H2” [NH 4]2[S 2O8] 2[NH 4][HSO 4] + H 2O2 H2O2 stabilizer catalytic cycle used in the industrial manufacture of hydrogen peroxide 9 H2O2 H2O2 + - o H2O2 + 2H + 2e ⇌ 2H 2O E = +1.78 V + - o O2 + 2H + 2e ⇌ H2O2 E = +0.70 V Cl 2 + H 2O2 → 2HCl + O 2 10 Peroxo complexes − µ 2− [V(O 2)2(O)(bpy)] [Mo 2(O 2)4(O) 2( -OOH) 2] 11 Polysulfanes: H 2SX n = 2 2H 2S + Sn nCl 2 H2Sn+2 + 2HCl 2- Polysulfides: [S X] 2- [S 6] 2- [Mn(S )(S )] 2- [Zn(S 4)2] 5 6 µ 4- 2- [(S 6)Cu( -S8)-Cu(S 6)] [AuS 9] 12 2- 2- Polyselenides and polytellurides: [Se x] and [Te x] DMF* 3Se + K 2Se 2 K2[Se 5] *DMF = Dimethylformamide = 4Se + K 2Se 2 + 2[Ph 4P]Br [Ph 4P] 2[Se 6] + 2KBr DMF, 15-crown-5 3 Se + K 2Se 2 [K(15-crown-5)] 2[Se 5] 1,2-diaminoethane, crypt-222 2K + 3 Te [K(crypt-222)] 2[Te 3] 2- 2- [Te 5] [Te 8] O 141 pm 103° F F 13 Sulfur fluorides and oxofluorides S2F10 SOF 2 14 Sulfur chlorides and oxochlorides 206 pm 1/4S 8(l) + Cl 2(g) - S2Cl 2 193 pm Reaction Chemistry S 2Cl 2 2SO 2 + S 2Cl 2 + 3Cl 2 4SOCl 2 Cl-S-S 108° SO 3 + SCl 2 SOCl 2 + SO 2 Internal dihedral angle = 84° 2SCl 2 S2Cl 2 + Cl 2 Reaction Chemistry of SOCl 2 RCO 2H + SOCl 2 RC(O)Cl + SO 2 + HCl SOCl 2 SO 2Cl 2 15 TeF SeF 4 4 Se 4Cl 16 Tellurium halides 16 2− = MO diagram for octahedral [ECl 6] (E Se or Te) Oxides of Sulfur SOCl 2 + Ag 2S -430 K S2O + 2AgCl HS 7H + SOCl 2 → S8O S8 ----CF 3C(O)OOH → S8O 17 - [(SO ) N ]- [SO 2N3] 2 3 3 18 Gas phase form of SO 3 also exists as a trimer of SO 4 units. Solid state form exists as polymeric chains Oxides of selenium and tellurium [Te O F ]3- 3 6 3 SeO 3 tetramer 19 Oxoacids and their salts: S H2S + HSO 3Cl -low temp- H2S2O3 + HCl ClSO 3H ClSO 3H H2O2 -HCl H2SO 5 -HCl H2S2O8 20 2− H SO (g) [S 2O6] 2 4 H2SO 4 (l) Sulfur-Nitrogen Compounds 21 Potential diagrams (values in V) for sulfur, selenium and tellurium at pH = 0. 22.