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Noble Gases

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Introduction

Chemistry Homework

Noble Gases

The six noble gases are found in group 18 of the periodic table. These elements were considered to be inert gases until the 1960's, because their oxidation number of 0 prevents the noble gases from forming compounds readily. All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others), making them stable.

Radon is a hazardous radioactive gas and will not be considered further here.

The appearances in this group are in general similar; they are all colourless gases at room temperature with low melting points and boiling points. As expected, their melting point, boiling points and densities have a steady change as the relative atomic mass increases. As the name suggests, all the elements in this Group are gases.

Their general reactivity is almost none they are generally unreactive, because they have closed-shell configurations. The noble gases all exist as separate single atoms (i.e. monatomic molecules.) Until 1962, no compounds of the noble gases were known. Chemists thought they were completely unreactive. Hence they were called inert gases. Nowadays, several compounds of them are known and the name inert has been replaced by noble

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Middle

He

2

4.003

4.216

Ne

10

20.180

27.10

Ar

18

39.948

87.29

Kr

36

83.30

120.85

Xe

54

131.29

166.1

1st Ionisation Energy/kJ mol-1

Atomic Radius/nM

He

2372.3

0.128

Ne

2080.6

0.160

Ar

1520.4

0.174

Kr

1350.7

0.189

Xe

1170.4

0.218

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Conclusion

As with the other noble gases, krypton is isolated from the air by liquefaction.

One of the naturally occurring non-radioactive isotopes of krypton, Kr-86 (17.3%) is used as the basis for the current international definition of the meter. One meter is 1,650,762.73 wavelengths of the red-orange spectral line of krypton-86.

Also discovered by Ramsay and Travers in 1898, xenon (from the Greek xenos for "strange") is the rarest of the stable noble gases in the air. It is still recovered by liquefaction techniques and is widely used in strobe lamps.

In 1962 the first noble gas compound was produced by Neil Bartlett, combining xenon, platinum and fluorine. It is now possible to produce xenon compounds in which the oxidation states range from +2 to +8(!).

Discovered in 1900 by Friedrich Dorn, radon is a radioactive noble gas now regarded as a potential health hazard in some homes. It also has medical applications for cancer treatment. Its original name was to be niton for "shining" but it was eventually named as a derivative of radium. Radon is found in underground deposits where is it produced by uranium and radium decay.

Radon fluoride (RnF) has been produced and the element glows with a yellow light in the solid state.

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