1. Ch 18. Group 18

2. 2 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) 1895 Lord Raleigh N 2 in air is denser than N 2 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 (t 1/2 ~ 4 days)

3. 3 Applications He coolant (bp = 4.2K, lowest known); esp. for superconductors (MRI/NMR) balloons, etc. lifting power = 1 kg / m 3 diving air tanks, He has a lower blood solubility than N 2 Other gases inert atmosphere (ex – welding) lighting (electric discharge to get excited state)

4. 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. 5 Compounds Consider MO theory – bonding depends on symmetry and orbital energies, trends throughout the p-block Xe (g) + F 2 (g)  XeF 2 (use excess Xe) Xe + 2 F 2  XeF 4 (D 4h ) Xe + 3 F 2  XeF 6 (use excess F 2 ) XeF 2 colorless sublimable solid linear molecular structure, isoelectronic w IF 2 -, Xe-F b.l. ~ 200 pm 400  C or uv

6. 6 XeF 2, XeF 4, and XeF 6 XeF 6 or (XeF 5 + F - ) n XeF 4 crystals

7. 7 XeF n reactions XeF 2 + SbF 5  XeF + SbF 6  (s) + HN(SO 2 F) 2  XeF + N(SO 2 F) 2  (s) + HF + HSO 3 F  XeF + SO 3 F  (s) XeF 6 + SbF 5  XeF 5 + SbF 6  (s) XeF 6 + 2 MF  M 2 XeF 8 square anti-prism (Xe-F) + isoelectronic w IF, Xe-F b.l. ~ 195 pm

8. 8 XeF + and XeF 5 + < F eq XeF eq = 87° < F ax XeF eq = 78° XeF 5 + RuF 6 - (s) XeF + SO 3 F - XeF + N(SO 2 F) 2 -

9. 9 Xenon oxides XeF 2 + H 2 O  Xe + 2 HF + ½ O 2 XeF 6 + H 2 O  XeO 3 (aq) + 6 HF (metathesis instead of hydrolysis is possible under controlled conditions) XeO 3 + OH   HXeO 4   disproportionates in base XeO 6 4  + Xe XeO 3 is endoergic, and explosive (perxenate)

10. 10 Xenon oxyfluorides also: XeO 2 F 2, XeOF 4, etc

11. 11 Other compounds AuF 3  [AuXe 4 ](Sb 2 F 11 ) 2 Xe(g) SbF 5 /HF (superacid)

12. 12 Krypton chemistry Kr + F 2  KrF 2 (s) unstable at RT,  H f ~ + 20 kJ/mol KrF 2 + SbF 5  (KrF) + SbF 6 - a few other LA complexes are known h -78°C