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Noble GasesDoc Brown's Chemistry KS4 Science GCSE/IGCSE/O Level Chemistry Revision Notes

The GROUP 0 The Noble Gases 

 The Group 0 elements, the NOBLE GASES consist of helium, neon, argon, krypton, xenon and radioactive radon. The physical properties of the noble gases are described and the group trends of noble gases in terms of melting points, boiling points, density, chemical reactivity and atomic radii and also the 'few' chemical properties of some noble gases e.g. xenon are mentioned. The uses of noble gases are also described and explained.

Keywords and phrases for Group 0 Noble Gases * argon uses * compounds * data on elements * electron arrangement * helium uses * introduction * krypton uses * neon uses * radon dangers * xenon uses * uses of noble gases * extra information

GCSE m/c QUIZ on Noble Gases * (c) doc b Multi-word fill worksheet on the Noble Gases

PLEASE Note A Level Students GCE AS/A2/IB Advanced Level Chemistry Notes on the Group 0/18 Noble Gases

BUT reading this page reminds you of what you theoretically leaned from GCSE/IGCSE/O Level courses on noble gases!

So this page can act as a primer for the study of noble gases helium, neon, argon, krypton, xenon


 

Where are the Group 0 Noble Gases in the Periodic Table?

Periodic Table

The Group 0 Noble Gases form the last vertical column on the right of the Periodic Table, where you find most of the non-metallic elements. Therefore the Noble Gas is the last element on ANY complete period. At the bottom of Group 0 is radioactive noble gas element radon (Rn) which is not shown.

Note: The group number for 1 to 7  is equal to the maximum valency of the element (except for O and F). Using 0 to denote the Group number of Noble Gases is very historic since no compounds of Noble Gases where known until the 1960s. Now, since compounds of xenon exhibiting a valency of up to 8 have been synthesised. Because of the horizontal series of elements e.g. like the Sc to Zn block (10 elements), Groups 3 to 7 can also be numbered as Groups 13 to 17, and Group 0 can be numbered Group 18, to fit in with the actual number of vertical columns of elements. This can make things confusing, but there it is, classification is still in progress!

 

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Introduction to the Group 0 Noble Gases (see data table below)
  • The "Noble Gases" are the last group in the Periodic Table i.e. they form the last elements at the end of a period, the final vertical column of elements.

    • In descending order, the six noble gases are ...

      • helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn).

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

  • They are very unreactive elements because the highest occupied electron level is complete, meaning they have a full shell of outer electrons! (see diagrams below). They have no great '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 are sometimes referred to as inert gases, because of their lack of chemical reactivity.

    • In fact their lack of reactivity was one reason why they were some of the last naturally occurring elements of the periodic table to be discovered. They were discovered because the density of chemically made nitrogen was different from the nitrogen obtained from air after removal of oxygen. Therefore. it was reasoned that there must be more 'unknown' gases in air. Careful low temperature fractional distillation of liquified air revealed the noble gases, and this is how they are usually obtained in industry.

  • 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 - see point above and diagrams below.

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

  • Down the Group 0 with increasing atomic number for the Noble Gas elements ...

    • ... the melting point and boiling point of noble gases steadily increase down the group (see data) because the weak intermolecular forces increase with the size of the atom.

      • This is because the increase in the number of electrons, due to an extra electron shell from one noble gas down to the next, in the increasingly bigger atom leads to an increase in these weak electrical attractive forces.

      • i.e. the strength of the intermolecular forces or intermolecular bonding forces between the atoms increases, so more energy (higher kinetic energy, higher temperature) is needed to boil the condensed Noble Gas.

    • ... the density of noble gases steadily increases down the group (see data)

    • ... down the group, theoretically, the noble gases are more likely to react and form a compound with very reactive elements like fluorine eg

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

      • The most reactive Noble Gas would be radon BUT this is a highly dangerous radioactive gas!

      • Some VERY unstable compounds have been made from argon and krypton.

      • The reason for the lack of reactivity by noble gases is explained in the box below.

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Electron structure and reactivity of noble gases

The first 3 Noble Gases, showing their electron arrangements with full very stable outer shells making the noble gas elements VERY unreactive. Noble gas atoms have a full, and very stable, outer electron shell. They are very reluctant to share electrons to form a covalent bond OR lose/gain electrons to form an ionic bond. As the atom gets bigger, the outer electrons are less strongly held and the lower member noble gases e.g. xenon can be tempted into chemically reacting with VERY reactive chemical reagents like fluorine (the most reactive non-metal).

Noble Gases Noble Gases Noble Gases

  

Selected data on the Group 0/8 Noble Gases (more AS-A2 data)

Chemical symbol and name

Atomic number Electron arrangement Melting point Boiling point Density g/cm3 Atomic radius pm (10-12m) and nanometres nm (10-9m)
He helium 2 2 -272oC , 1K -269oC , 4K 0.0002 49 and 0.049
Ne neon 10 2.8 -249oC , 24K -246oC , 27K 0.0008 51 and 0.051
Ar argon 18 2.8.8 -189oC , 84K -186oC , 87K 0.0018 94 and 0.094
Kr krypton 36 2.8.18.8 -157oC , 116K -152oC , 121K 0.0037 109 and 0.109
Xe xenon 54 2.8.18.18.8 -112oC , 161K -108oC , 165K 0.0059 130 and 0.130
Rn radon 86 2.8.18.32.18.8 -71oC , 202K -62oC , 211K 0.0097 136 and 0.136

  

 Uses of the Group 0/8 Noble Gases

The unreactive noble gases are non-flammable and this inertness is an important characteristic when understanding the uses of noble gases.

Uses of He helium Noble Gases Helium gas is much less dense than air (lighter) and is used in party balloons and 'airships' because it 'floats' in air! Because of its inertness helium 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. Liquid helium is used to achieve very low temperature in cryogenics technology.
Uses of Ne neon Noble Gasesjust like this website! Neon gives out light when high voltage electricity is passed through it, so neon is used in glowing 'neon' advertising signs and fluorescent lights. 
Uses of Ar argon Noble GasesNoble Gases 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. Argon 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. Argon bubbles are used to stir mixtures in steel production. Argon is the cheapest noble gas to produce, it has the biggest % of any noble gas in air.
Uses of Kr krypton   Krypton is not used by superman! BUT krypton is used in fluorescent bulbs, flash bulbs and laser beams.
Uses of Xe xenon   Xenon is good for winning scrabble games! AND xenon also used in fluorescent bulbs, flash bulbs and lasers!
Rn radon Noble Gases 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, especially in granite areas because it is a decay product of unstable uranium isotopes. 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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Extra 'bits and bobs' on THE NOBLE GASES

% 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)
Radon dangers Rocks, e.g. granite, can contain uranium metal compounds which are radioactive. When they 'decay' radioactively, radioactive and harmful radon gas can be formed.
Compounds of Noble Gases - yes they do exist! From the early 1960's 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 + 2F2 => XeF4 (using Ni catalyst 60oC, easy if you know how! and another catalytic bonus from a transition metal!)

   

 

PLEASE Note A Level Students GCE AS/A2/IB Advanced Level Chemistry Notes on the Group 0/18 Noble Gases

BUT reading this page reminds you of what you theoretically leaned from GCSE/IGCSE/O Level courses on noble gases!

So this page can act as a primer for the study of noble gases helium, neon, argon, krypton, xenon


Revising for KS4 Science IGCSE/O level/GCSE Chemistry Information Study Notes for revising for AQA GCSE Science, Edexcel GCSE Science/IGCSE Chemistry & OCR 21st Century Science, OCR Gateway Science, CCEA/CEA GCSE science-chemistry, WJEC GCSE science-chemistry (revise courses equal to US grades 8, 9, 10) for science chemistry courses revision guides


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