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+ and XeF5+

< FeqXeFeq = 87°

< FaxXeFeq = 78°

XeF5+RuF6

- (s) XeF+SO3F-

XeF+N(SO2F)2-

9

Xenon oxidesXeF2 + 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

Other compounds

AuF3 [AuXe4](Sb2F11)2

Xe(g)

SbF5/HF(superacid)

12

Krypton chemistry

Kr + F2 KrF2(s)

unstable at RT, Hf ~ + 20 kJ/mol

KrF2 + SbF5 (KrF)+ SbF6-

a few other LA complexes are known

h

-78°C