Noble Gases - Properties
The Elements of Group 18
(8A, VIII, VIIIA)
The Noble Gases
He, Ne, Ar, Kr, Xe, Rn
Valence electron configuration: ns2np6
Occurrence
Properties and Uses
Air is the only source of most noble gases:
0.000524% He (5.2 ppm)
0.001818% Ne
0.934% Ar
1 ppm Kr
0.05 ppm Xe
He from natural gas up to 8% He by volume.
Pure elements isolated by fractionation
Electric discharge lamps.
Lasers and flashlamps.
Inert atmosphere chemistry.
Metallurgy and semiconductors.
Superconducting magnets.
NMR, MRI, particle accelerators.
Blimps
An MRI image of a head.
Group 18: The Noble Gases
Noble Gases
“Electron-rich”: Lewis base properties?
Gas-phase PA
He
178 kJ/mol
Ne
199
Ar
369
Kr
424
Xe
499
H2O
690
NH3
853
PA (proton affinity) = -∆
∆H for B + H+ → BH+
Long thought to be chemically inert, called the
Inert Gases
Pauling (1930s) predicted reactivity of xenon to
form oxide and fluoride compounds.
Early 1960s: observation that O2 reacted with PtF6
to give O2PtF (really O2+ PtF6-)
Xe same ionization energy and size as O2
Synthesis of XePtF6
Subsequently
XeF2, XeF4, XeOF2, XeF6, XeO3, XeO4 and
H4XeO6
Xenon Compounds
Crystals of xenon tetrafluoride
under magnification.
All xenon compounds are strong oxidizing agents:
XeF2(aq) + 2 H+(aq) + 2 e- → Xe(g) + 2 HF(aq)
E° = +2.64 V
Intermolecular Attractions in XeF2, XeF4
Enthalpy Diagram for formation of XeF2
• Xe does not react directly with O2 or Cl2
• No other noble gases combine directly with F2
Electron group geometries for XeF2, XeF4, XeF6
Periodic Trends in Bonding
Metallic character decreases from left to right across the table.
capped trigonal prism
capped octahedron
pentagonal bipyramid