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G.VENUGOPAL �{PGT in Chemistry}�JNV2 PRAKASAM—A.P

E-Content

Group 18 Elements

Class XII

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GROUP 18 ELEMENTS

  • HELIUM(He)
  • NEON(Ne)
  • ARGON(Ar)
  • KRYPTON(Kr)
  • XENON(Xe)
  • RADON(Rn)
  • THESE ELEMENTS ARE ALSO CALLED ZERO GROUP ELEMENTS / NOBLE GASES / INERT GASES.

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  • ALL THESE ELEMENTS HAVE nS2,nP6 VALENCE SHELL CONFIGURATION EXCEPT HELIUM (1S2)
  • EXCEPT RADON,ALL ARE AVAILABLE IN THE ATMOSPHERE.
  • COMMERCIAL SOURCE OF HELIUM IS NATURAL GAS.
  • RADON IS OBTAINED AS A DECAY PRODUCT OF RADIUM-226.

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  • ALL THESE ELEMENTS ARE CHEMICALLY UNREACTIVE GASES ,HENCE TERMED AS NOBLE GASES.
  • THEY ARE UNREACTIVE DUE TO CLOSED nS2,nP6 SHELL STRUCTURE.
  • DUE TO STABLE ELECTRONIC CONFIGURATION,THEY HAVE VERY HIGH IONISATION ENERGIES,WHICH DECREASE FROM He TO Xe.
  • ATOMIC SIZE DECREASE DOWN THE GROUP.

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  • HAVE NO TENDENCY TO GAIN ELECTRONS RESULTING IN THE LARGE POSITIVE VALUES OF ELECTRON GAIN ENTHALPY.
  • ALL THESE GASES ARE MONOATOMIC,COLOURLES,ODOURLES, AND TASTELESS.
  • SPARINGLY SOLUBLE IN WATER.
  • HAVE VERY LOW MELTING AND BOILING POINTS DUE TO MONOATOMIC NATURE AND WEAK DISPERSION FORCES.

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  • HELIUM HAS THE LOWEST BOILING POINT(4.2K) OF ALL THE KNOWN SUBSTANCES.
  • HELIUM CAN DIFFUSE THROUGH RUBBER,GLASS,PLASTICS.

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CHEMICAL PROPERTIES

  • ALL THESE ELEMENTS ARE LEAST REACTIVE DUE TO COMPLETELY FILLED nS2, nP6 CONFIGURATION, HIGH IONISATION VALUES AND MORE POSITIVE ELECTRON GAIN ENTHALPIES.
  • FORMATION OF O2+PtF6- MADE NEIL BARTLETT TO THINK OF COMPOUNDS OF Xe, BECAUSE BOTH Xe AND O2 HAVE IDENTICAL IONISATIONA VALUES 1170KJ/Mol AND 1175KJ/Mol RESPECTVELY.

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  • BARTLETT MADE Xe+PtF6- BY MIXING PtF6 AND Xe.
  • XENON ONLY FORMS COMPOUNDS BECAUSE OF IT’S RELATIVELY BIG SIZE AND LOW IONISATION ENERGY.
  • XENON FORMS COMPOUNDS WITH MORE ELECTRO NEGATIVE ELEMENTS LIKE OXYGEN AND FLUORINE.

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  • Xenon fluorides react with fluoride ion acceptors to form cationic species and fluoride ion donors to form fluoroanions.
  • XeF2 + PF5 → [XeF]+ [PF6]– XeF4 + SbF5 → [XeF3]+ [SbF6]–
  • XeF6 + MF → M+ [XeF7]– (M = Na, K, Rb or Cs)

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  • Hydrolysis of XeF4 and XeF6 with water gives Xe03.
  • 6XeF4 + 12 H2O → 4Xe + 2Xe03 + 24 HF + 3 O2
  • XeF6 + 3 H2O → XeO3 + 6 HF
  • Partial hydrolysis of XeF6 gives
  • oxyfluorides, XeOF4 and XeO2F2.
  • XeF6 + H2O → XeOF4 + 2 HF
  • XeF6 + 2 H2O → XeO2F2 + 4HF

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USES

  • Helium is a non-inflammable and light gas. Hence, it is used in filling balloons for meteorological observations.

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  • It is also used in gas-cooled nuclear reactors. Liquid helium (b.p. 4.2 K) finds use as cryogenic agent for carrying out various experiments at low temperatures.

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  • It is used to produce and sustain powerful superconducting magnets which form an essential part of modern NMR spectrometers and Magnetic Resonance Imaging (MRI) systems for clinical diagnosis.

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  • It (He) is used as a diluent for oxygen in modern diving apparatus because of its very low solubility in blood.

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  • Neon is used in discharge tubes and fluorescent bulbs for advertisement display purposes. Neon bulbs are used in botanical gardens and in green houses

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  • Argon is used mainly to provide an inert atmosphere in high temperature metallurgical processes (arc welding of metals or alloys) and for filling electric bulbs. It is also used in the laboratory for handling substances that are air-sensitive. There are no significant uses of Xenon and Krypton. They are used in light bulbs designed for special purposes.

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THANK

YOU

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