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The Main Group Elements Sulfur, Selenium, Tellurium, and Polotinum

The Main Group Elements Sulfur, Selenium, Tellurium, and Polotinum. Group Tendency (p230). Lower electronegativities: less ionic character Character of multiple bonding for sulfur: d π -p π bonding, litlle if any p π -p π such as S─O in SO 4 2– Valence: not confined to 2, more to 4

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The Main Group Elements Sulfur, Selenium, Tellurium, and Polotinum

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  1. The Main Group Elements Sulfur, Selenium,Tellurium, and Polotinum

  2. Group Tendency (p230) • Lower electronegativities: less ionic character • Character of multiple bonding for sulfur: dπ-pπ bonding, litlle if any pπ-pπ such as S─O in SO42– • Valence: not confined to 2, more to 4 such as SF6, and Te(OH)6 • Tendency catenation for sulfur: equaled tor exceeding only by carbon Sn 2– For O, Se and Te, weaker in this tendency

  3. Group Tendency (p230) • The increasing size of the atoms and the decreasing electronegativity on going from S to Po are responsible for the changes in the properties of the elments. The examples as: • The decreasing stability of H2E • The increasing tendency to for complex ions SeBr62– • The metallic properties for Te and Po MO2 are ionic and basic, reacting with HCl to give the chlorides

  4. Key Information (p231) • Name: Sulphur or Sulfur • Symbol: S • Atomic Number: 16 • Atomic Weight: 32.065amu • Group Number: 16

  5. Group Name: Chalcogen • Block: p-block • Standard State: Solid at 298K • Color: Bright yellow • Classification: Non-metallic

  6. The History of Sulfur • Sulfur dates back as far as ancient times. • It Genesis it was referred to as brimstone, and in 700-600 BC the Assyrian texts called it the “product of the riverside.” • It is thought that the Chinese discovered gun powder around the 12th century.

  7. The person that should be credited with convincing the scientific community that sulfur was an element around 1777 is Antoine Lavoisier. • Sulfur is also know as one of the elements that has an alchemical symbol.

  8. Common Isotopes

  9. Isolation • Sulfur is readily available, so it is not necessary to make it. • It is a native element in nature and can be extracted by the Frasch process. • This process requires superheated water and steam to melt the sulfur. Commercial success for this process depends on ideal geological conditions.

  10. Hydrogen Sulfide, H2S, is a main impurity in natural gas and it must be removed before the gas can be used. • It is removed by absorption and regeneration followed by a catalytic oxidation using porous catalysts like Al2O3 or Fe2O3 (Claus process). • 8H2S + 4O2 —> S8 + 8H2O

  11. Additional Properties • Melting Point: 112.8°C • Boiling Point: 444.6°C • Density at 293K: 2.07 g/cm3 • Crystal Structure: Orthorhombic • S8 and S∞

  12. Reactions • Sulfur burns in air to form dioxide sulfur(IV)oxide. • S8(s) + 8O2(g) —> 8SO2(s) • Sulfur reacts with all halogens upon heating. • S8 + 4Cl2 —> 4S2Cl2(l) • S2Cl2(l) + Cl2 <=> 2SCL2(l)

  13. Sulfur also reacts with bases. • S8(s) + 6KOH(aq) —> 2K2S3 + K2S2O3 + 3H2O(l) • Sulfur also reacts with Lewis Acids • S8(s) + 3SbF5 S82+ + 2SbF6– + SbF3

  14. Key Information • Name: Selenium • Symbol: Se • Atomic Number: 34 • Atomic Weight: 78.96amu • Group Number: 16

  15. Group Name: Chalcogen • Block: p-block • Standard State: Solid at 298K • Color: Grey, Metallic lustre • Classification: Non-metallic

  16. The History of Selenium • Selenium was discovered in 1817, by Jons Jacob Berzelius. • He originally reported the impurity in sulphuric acid to be tellurium, but latter found that is was selenium instead of tellurium.

  17. Isolation • Selenium is an element that is readily available, so it is not necessary to make it. • Most selenium is made as a byproduct of copper refining. • It also accumulates in the residues from sulphuric acid manufacture.

  18. Extraction is a two step process: • Cu2Se +Na2CO3 + 2O2—> 2CuO + Na2SeO3 + CO2 • The selnite is acidified with sulphuris acid • H2SeO3 + 2SO2 + H2O —> Se + 2H2SO4

  19. Additional Properties • Melting Point: 217.0°C • Boiling Point: 684.9°C • Density at 293K: 4.79 g/cm3 • Crystal Structure: Hexagonal

  20. Isotopes

  21. Reactions • Selenium reacts with air: • Se8(s) + 8O2—> 8SeO2(s) • Selenium reacts with halogens: • Se8(s) + 16F2(g) —> 8SeF4(s) • Se8(s) + 16Cl2(g) —> 8SeCl4(s) • Se8(s) + 16Br2(g) —> 8SeBr4(s) • Se8(s) + 16I4(s) —> 8SeI4(s)

  22. Hydrides EH2 (p232) • Preparation: • M2E + H+ H2E • MeC(S)NH2 + 2H2O H2S • Toxicity: H2S Far exceeds that of • HCN • Thermal Stability and bond strength: decrease down the series Why ? • Acidity in water : increase Why ? • Reducity: H2Sx Sulphane, Polysulfide • Na2S5, K2S6 and BaS4 as ligand

  23. Metal Sulfides • Na2S and BaS dissolve in water • Cr2S3 and Al2S3 hydrolysis fully • MnS and ZnS dis. dilute HCl • CdS Concentric HCl • CuS HNO3 • HgS HNO3 + HCl • Note: Ksp and Complex; Color

  24. Halides of Group 16 Sulphur, selenium and tellurium have extensive halogen chemistries. S forms stable compounds with F, Cl, Br unstable compounds with I Se and Te form stable compounds with all halogens

  25. S8 + 24F2 8SF6 Fluorine brings out the highest oxidation states SF6, SeF6 andTeF6 are all stable compounds

  26. There are some REALLY interesting in its structures with fluorine S2F10 FSSF, FSeSeF? SSF2, SeSeF2? SF2, SeF2 S2F4 SF4, SeF4 TeF4

  27. The structures of the fluorides are all readily modeled by VSEPR SF4 (10 valence electrons) is therefore trigonal bipyramidal with L.P. in axial position NOT tetrahedral! Where asymmetry exists in the S-F structures, compounds are reactive, when symmetric, unreactive • SF4 – highly reactive gas • SF6 – very unreactive • -used to blanket electrical transformers • -S-F bond remains reactive, reactions kinetically • hindered Less sterically crowded Se and Te hexafluorides are more reactive.

  28. Te2Cl SCl2, SeCl2, TeCl2 S2Cl2, Se2Cl2 S3Cl2, Se3Cl2 SCl4, [SeCl4]4, [TeCl4 ]4 Te2Br SeBr SeBr2, TeBr2 S2Br2, Se2Br2 [SeBr4]4, [TeBr4 ]4 Lower halides

  29. Te2I TeI Te4I4 S2I2, [TeI4 ]4

  30. Just because a compound isn’t stable, doesn’t mean that folks won’t try to make something like it: S – I compounds: Only S2I2 known and it is quite reactive [S7I]+[AsF6]- [S2I4]2+[AsF6-]2 [SeI3+][AsF6-] [TeI3+][AsF6-] [SeBr3+][AsF6-] [TeBr3+][AsF6-] [SBr3+][AsF6-]

  31. Sulfur Oxo-chlorides (p234) • Thionyl chloride (SOCl2) • SO2 + PCl5 SOCl2 + POCl3 • SOCl2 + 2H2O SO2 + 2HCl • Used as dehydratant to prepare anhydrous chlorides • Sulfuryl Chlride (SO2Cl2) • SO2 + Cl2 SO2Cl2 • Both can react with ammonia

  32. Oxides: SO2 • AB2E SP2 • V-shape • Lewis base: S / O donar atom • Lewis acid: π* orbital • Solubility in water: good • SO2 + xH2O SO2 ·xH2O (gas hydrate) HSO3– • K = 1.3E-2 .. .. .. .. ..

  33. SO3 • Preparation: SO2 react with O2, catalyzed by Platinum sponge, V2O5, NO • Structure: planar (g); cycle or polymer (s) • Solubility in water: easy, giving H2SO4

  34. SeO2 is exclusively polymeric (consistent with move to more polar/ionic character as group is descended). Linear zig-zag structure. SeO3 is a cyclotetramer (cf SO3).

  35. Oxo Acids

  36. Suluric, Selenic and Telluric acids (p238) • Acidic anhydrides: AO3 • Preparation: H2SO4,SO3 absorbed in concentrated H2SO4; Te(OH)6, oxidation of TeO2 by H2O2 Why ? • Strong dehydratant: H2SO4 and H2SeO4 • Strong oxidizing agents: H2SO4 < H2SeO4Why ? • The isomorphism of salts: MI2SO4 ·MIISO4·6H2O MI2SO4 ·M2III(SO4)3·24H2O • Solubility of salts in water: good (ionic character) but…

  37. Thiosulfates (p238) • Preparation: SO32- + S S2O32- S + SO2 • To be easily oxidized S2O32- + I2S4O62- Cl2 SO42- • As ligand (used in photography) [Ag(S2O3)]- [Ag(S2O3)2]3- AgS + SO42- Δ H+ S S O O O H2O

  38. Dithionites • Sulfite SO32- + I2HSO4- S2O42- • Na2S2O4 strong reductant Dithionates • MnO2 + 2SO32- + 4H+ Mn2+ + S2O62- + 2H2O • S4O62- SO2, Zn O O S S O O O O

  39. Peroxodisulfate 2HSO4- - 2e– S2O82- + 2H+ 8H2O + Mn2+ + S2O82-MnO4- + 2SO42- + 16H+ Ag2+ Ag+

  40. Disulphurate • H2SO4 + SO3 H2S2O7 • 2KHSO4K2S2O7 + H2O • K2S2O7 + Ai2O3Al2(SO4)3 + K2SO4 Δ Δ Δ

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