Group VIIIA The Noble Gases

The first experimental evidence for the noble gases was obtained by Henry Cavendish in 1766. In a series of experiments on air, he was able to sequentially remove nitrogen (then known as phlogisticated air ), oxygen ( dephlogisticated air ), and carbon dioxide ( fixed air ) from air by chemical means, but a small residue, no more than one part in 120, resisted all attempts at reaction. The nature of Cavendish s unreactive fraction of air remained a mystery for more than a century. This fraction was, of course, eventually shown to be a mixture of argon and other noble gases.  

During a solar eclipse in 1868, a new emission line, matching no known element, was found in the spectrum of the solar corona. J. N. Locklear and E. Frankland proposed the existence of a new element named, appropriately, helium (Greek, helios, sun). The same spectral line was subsequently observed in the gases of Mount Vesuvius. 

Within 3 years, Ramsay and M. W. Travers had isolated three additional elements by low-temperature distillation of liquid air, neon (Greek, neos, new), krypton (Greek, kryptos, concealed), and xenon (Greek, xenos, strange). The last of the noble gases, radon, was isolated as a nuclear decay product in 1902. 

Important properties of the noble gases are summarized in Table 8-17. 

Properties of the Group 18 (VIHA) Elements The Noble Cases 

In our discussions of bonding, we pointed out the relative stability of the electron configurations of the Group VIIIA noble gases. For many years, it was thought that because the atoms of these elements had completed octets, Ihe noble gases would be completely unreactive. Consequently, these elements were known as inert gases. Compounds of krypton, xenon, and radon have since been prepared, however, so (he term is not quite appropriate. 

Before the discovery of argon, some lines in the spectrum of the sun were ascribed to an element not yet known on earth. This element was called helinm (from the Greek helios, meaning sun ). In 1895, Ramsay and the Swedish chemist Per Theodor Cleve (working independently) announced the discovery of helium gas in the mineral cleveite (a uranium ore) by identifying the spectrum of helium. 

Several years later, Ramsay discovered neon, krypton, and xenon by fractional distillation of liquid air. Radon was discovered in 1900 as a gaseous decay product of radium. 

The product actually has variable composition and can be represented by the formula XelPtFgln, where n is between 1 and 2. 

This photomicrograph shows crystals obtained in the experiment that first produced a binary compound of xenon. 

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