ch 18. group 18

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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) - PowerPoint PPT Presentation

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  • Ch 18. Group 18

  • *Elements1785 Henry Cavendish air contains < 1% of gas that does not react with O2 under electric discharge1868 (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 compoundsHe impurity in natural gas (from radioactive decay underground)Ar to Xe distillation of liquid airRn none, intensely radioactive (t1/2 ~ 4 days)

  • *ApplicationsHe coolant (bp = 4.2K, lowest known); esp. for superconductors (MRI/NMR) balloons, etc. lifting power = 1 kg / m3diving air tanks, He has a lower blood solubility than N2Other gasesinert atmosphere (ex welding)lighting (electric discharge to get excited state)

  • *Noble gas chemistry I / eVHe 24.6Ne 21.6Ar 15.8Kr 14.0Xe 12.1Rn 10.7

  • *CompoundsConsider 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

  • *XeF2, XeF4, and XeF6XeF6 or (XeF5+F-)nXeF4 crystals

  • *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

  • *XeF+ and XeF5+< FeqXeFeq = 87 < FaxXeFeq = 78 XeF5+RuF6- (s)

  • *Xenon oxidesXeF2 + H2O Xe + 2 HF + O2

    XeF6 + H2O XeO3 (aq) + 6 HF (metathesis instead of hydrolysis is possible under controlled conditions)XeO3 + OH HXeO4 disproportionates in baseXeO64 + Xe

    XeO3 is endoergic,and explosive(perxenate)

  • *Xenon oxyfluoridesalso: XeO2F2 , XeOF4, etc

  • *Other compounds

  • *Krypton chemistry

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