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Ch 18. Group 18

Ch 18. Group 18. Elements. 1785 Henry Cavendish air contains < 1% of gas that does not react with O 2 under electric discharge 1868 (Aug 18) Janssen / Lockyer solar eclipse, yellow line in solar spectrum (He)

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Ch 18. Group 18

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  1. Ch 18. Group 18

  2. Elements 1785 Henry Cavendish air contains < 1% of gas that does not react with O2 under electric discharge 1868 (Aug 18) Janssen / Lockyer solar eclipse, yellow line in solar spectrum (He) 1895 Lord Raleigh N2 in air is denser than N2 from ammonia (due to Ar in air sample) Commercial sources: no naturally occurring compounds He – impurity in natural gas (from radioactive decay underground) Ar to Xe – distillation of liquid air Rn – none, intensely radioactive (t1/2 ~ 4 days)

  3. Applications He coolant (bp = 4.2K, lowest known); esp. for superconductors (MRI/NMR) balloons, etc. lifting power = 1 kg / m3 diving air tanks, He has a lower blood solubility than N2 Other gases inert atmosphere (ex – welding) lighting (electric discharge to get excited state)

  4. Noble gas chemistry I / eV He 24.6 Ne 21.6 Ar 15.8 Kr 14.0 Xe 12.1 Rn 10.7

  5. Compounds Consider MO theory – bonding depends on symmetry and orbital energies, trends throughout the p-block Xe (g) + F2 (g)  XeF2 (use excess Xe) Xe + 2 F2  XeF4 (D4h) Xe + 3 F2  XeF6 (use excess F2) XeF2 colorless sublimable solid linear molecular structure, isoelectronic w IF2-, Xe-F b.l. ~ 200 pm 400 C or uv

  6. XeF2, XeF4, and XeF6 XeF6 or (XeF5+F-)n XeF4 crystals

  7. XeFn reactions XeF2 + SbF5 XeF+SbF6 (s) + HN(SO2F)2 XeF+N(SO2F)2 (s) + HF + HSO3F  XeF+SO3F (s) XeF6 + SbF5 XeF5+SbF6 (s) XeF6 + 2 MF  M2XeF8 square anti-prism (Xe-F)+ isoelectronic w IF, Xe-F b.l. ~ 195 pm

  8. XeF+N(SO2F)2- XeF+SO3F- XeF+ and XeF5+ XeF5+RuF6- (s) < FeqXeFeq = 87° < FaxXeFeq = 78°

  9. Xenon oxides XeF2 + H2O  Xe + 2 HF + ½ O2 XeF6 + H2O  XeO3 (aq) + 6 HF (metathesis instead of hydrolysis is possible under controlled conditions) XeO3 + OH HXeO4  disproportionates in base XeO64 + Xe XeO3 is endoergic, and explosive (perxenate)

  10. Xenon oxyfluorides also: XeO2F2 , XeOF4, etc

  11. Xe(g) AuF3 [AuXe4](Sb2F11)2 SbF5/HF (superacid) Other compounds

  12. h Kr + F2 KrF2(s) unstable at RT, Hf ~ + 20 kJ/mol KrF2 + SbF5 (KrF)+ SbF6- a few other LA complexes are known -78°C Krypton chemistry

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