(1) Group 0/18 The Noble Gases - their position in the periodic table, data and electron configurations

• The p-block Group of Noble Gases are the last group in the Periodic Table i.e. they form the last elements at the end of a period and are all non-metals.

• They are all non-metallic elements and all are colourless gases at room temperature and pressure with very low melting points and boiling points.

• They form 1% of air, and most of this is argon. All the noble gases, except radon, are separated by the fractional distillation of liquefied air.

• % in air by volume: 0.0005% He, 0.0018% Ne, 0.93% Ar, 0.0001% Kr, 0.00001% Xe, ?% Rn - impossible to be zero, but an extremely minute trace hopefully! (varies with local geology)

• Helium can also be obtained from natural gas wells where it has accumulated from radioactive decay (alpha particles become atoms of helium gas when they gain two electrons).

• They are very unreactive elements because the highest occupied electron level shell is completely full, meaning they have a full shell of outer electrons! They have no 'wish' electronically to share electrons to form a covalent bond or to lose or gain electrons to form an ionic bond. In other words, they are electronically very stable.

• They exist as single atoms, that is they are monatomic He Ne Ar etc. (NOT diatomic molecules as with many other gases - reasons given above). This is because of their electronic stability.

• Their very inertness is an important feature of their practical uses. 

• Down the Group with increasing atomic number ...

  • The melting point and boiling point steadily increase as the number of electrons in the atoms increases so does the 'intermolecular forces' - increase in instantaneous dipole - induced dipole forces still exist, even between individual atoms.

  • The density steadily increases.

  • They are more likely to react and form a compound with very reactive elements like fluorine.

• Stable compounds of xenon are now known and synthesised BUT not before 1961!

• The first 3 Noble Gases, showing their electron arrangements (in various styles) with full very stable outer shells.
• Helium, with one full shell only (outer = inner !) has the highest ionisation energy of any element and is chemically the most stable and least reactive of any element in the periodic table and has no meaningful chemistry.

• 1s2

  1s22s22p6

  [Ne]3s23p6

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(3) Uses of the group 0/18 Noble Gases

• HELIUM gas is much less dense than air (lighter) and is used in balloons and 'airships'. Because of its inertness it doesn't burn in air UNLIKE hydrogen which used to be used in large balloons with  'flammable' consequences e.g. like the R101 airship disaster! Helium is also used in gas mixtures for deep-sea divers.
• NEON gives out light when high voltage electricity is passed through it, so its used in glowing 'neon' advertising signs and fluorescent lights. 
• ARGON, like all the Noble Gases, is chemically inert. It used in filament bulbs because the metal filament will not burn in Argon and it reduces evaporation of the metal filament. It is also used to produce an inert atmosphere in high temperature metallurgical processes, eg in welding where it reduces brittle oxide formation reducing the weld quality. Its bubbles are used to stir mixtures in steel production. Argon is the cheapest to produce.
• KRYPTON Not used by superman! BUT is used in fluorescent bulbs, flash bulbs and laser beams.
• XENON used in fluorescent bulbs, flash bulbs and lasers.
• RADON Rocks, e.g. granite, can contain uranium metal compounds which are radioactive. When they 'decay' radioactively, radioactive and harmful radon gas can be formed. Radon has almost no uses, but does have dangers! Radio-isotopes of radon are produced by radioactive decay of heavy metals (e.g. uranium) in the ground. Can build up in cellars. Like all radio-isotopes it can cause cell damage (DNA) and ultimately cancer (see link below). However it is used in some forms of cancer treatment.

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(4) NOBLE GAS COMPOUNDS - yes they do exist!

• It was long recognised that noble gases had particularly stable electron configurations and were not expected to ever form stable chemical compounds.
• The highest s and p levels are full, as with all Group 0 noble gases and these electrons are most reluctant to engage in sharing electrons to form a covalent bond, and even less so, to form a positive ion.
• However an English chemist, Neil Bartlett, working in Canada in 1962, found that platinum hexafluoride (PtF₆), a very reactive compound itself, actually reacted with xenon to form a complex (XePtF₆), the very first noble gas compound ever!, and this was the start of the new branch of chemistry!
• So, from the early 1960's many noble gas compounds have been made, but only xenon compounds are stable and usually combined with oxygen and fluorine, which, not surprisingly, are the more reactive non-metals e.g.
• Xe(g) + 2F₂(g) ====> XeF₄(g)
  • (using Ni catalyst 60^oC)
  • The molecule has a square planar shape.
• There is now quite an extensive chemistry of xenon e.g.
  • xenon(II) fluoride XeF₂ (linear),
  • xenon(IV) fluoride XeF₄ (square planar),
  • xenon(VI) fluoride XeF₆
  • xenon(VI) oxide (xenon trioxide) XeO₃ which has a trigonal pyramid shape
  • xenon oxytetrafluoride XeOF₄ (Xe oxidation state +6)
  • the xenonate(VIII) ion XeO₆^4- ion exists in salts such as Na₄XeO₆.8H₂O which is stable and can be crystallised as a hydrated salt from aqueous solution.
    • This exhibits the maximum oxidation state theoretically expected for a noble gas below helium - 8 outer electrons that can be involved in covalent chemical bonding.
• I don't know of any stable compound of helium and argon, but argon(II) fluoride ArF₂ has been prepared at low temperatures (<40K, <-233^oC), via uv light shone onto frozen argon in the presence of fluorine?).
• Very unstable krypton(II) fluoride KrF₂ and krypton(IV) fluoride KrF₄ have been prepared, but despite the great reluctance of krypton to react - but we are dealing with fluorine, the most reactive element known and one of the most powerful oxidising agents known.