Oxygen, Sulphur, Selenium, and Tellurium

The three papers of specific relevance to this section concern the identification of the rare ion in the crystal structures of hydrates of strong 

Most organosulphur compounds for which structures have been reported are omitted from this chapter, since they are covered in the Organic Section. Most of the remaining crystal structures concern oxyanions of sulphur. 

Similar geometry for HSOi is found in ammonium bisulphate. S-OH distances in the two independent anions are 1.546 and 1.557 A whereas S-O distances lie between 1.419 and 1.455 A HO-S-O angles are generally greater than 109° and O-S-0 angles smaller. 

In the hydrogen disulphate anion in SeiCHSaOv), the localization of the hydrogen atom on one oxygen not only affects the immediate S-O bond length but also the S-O-S bridge which is unsymmetrical, with S-O distances of 1.59 A (to the sulphur to which the OH group is bonded) and 1.67 A. The S-OH distance is 1.56 A and all other S-O bonds are 1.43 0.02 A. 

A neutron diffraction study of sodium thiosulphate pentahydrate has shown that the large differences in S-O distances found in an earlier A -ray study were due to errors in the oxygen positions. The three S-O distances are 1.45—1.47 A, and the S-S length is 1.95 A. The terminal sulphur atom is involved in the extensive hydrogen-bonding scheme which is present. 

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Conductivity measurements in N/10 aqueous solution show the dissolved gas to be ionised to the extent of 50 per cent., whilst hydrogen selenide in Nj 10 solution is only 4-1 per cent, ionised. The acidity of the hydrides of the elements oxygen, sulphur, selenium and tellurium therefore falls into the regular series II2Te >H2Se >H2S >II20, in inverse order to the stability.6... 

Oxygen Substitutions. Let us recall to our recollections, a primary fact, recognized in science for a long time past, namely, that oxygen, sulphur, selenium, and tellurium form a group of equivalent bodies — of bodies which may replace one another mutually in their combinations, without altering the principal properties of the compounds into which they enter. 

Oxygen halides are dealt with in Chapter 11, p. 334. Sulphur, selenium and tellurium form many halides, and only a brief introduction to the subject is given here. 

Since tire alkali and alkaline metals have such a high affinity for oxygen, sulphur aird selenium they are potentially useful for the removal of these iron-metallic elements from liquid metals with a lower affinity for these elements. Since the hairdling of these Group I and II elements is hazardous on the industrial scale, their production by molten salt electrolysis during metal rehning is an attractive alternative. Ward and Hoar (1961) obtained almost complete removal of sulphur, selenium and tellurium from liquid copper by the electrolysis of molten BaCla between tire metal which functioned as the cathode, and a graphite anode. 

Because of the diversity displayed, tabulation of the properties of the whole of Gp.VIB is not very helpful the elements range from the very electronegative, non-metallic oxygen to the metallic polonium. Reactivity towards metals and hydrogen decreases from oxygen to tellurium. Sulphur, selenium and tellurium react energetically with fluorine and chlorine, rather less activity with bromine ... 

Oxygen being then the representative of sulphur, selenium, and tellurium, up to this time we have only carbon, hydrogen, and oxygen, as constituents of organic substances. 

At high temperatures oxygen reacts with the nitrogen in the air forming small amounts of nitrogen oxide (p. 210). Sulphur burns with a blue flame when heated in air to form sulphur dioxide SO2, and a little sulphur trioxide SO3. Selenium and tellurium also burn with a blue flame when heated in air, but form only their dioxides, Se02 and Te02. 

Sulphur is less reactive than oxygen but still quite a reactive element and when heated it combines directly with the non-metallic elements, oxygen, hydrogen, the halogens (except iodine), carbon and phosphorus, and also with many metals to give sulphides. Selenium and tellurium are less reactive than sulphur but when heated combine directly with many metals and non-metals. 

The elements yield tetravalent derivatives m special circumstances, iu which they function as the basic elements. In the case of oxygen they are termed oxonium salts sulphur yields sulphonium salts whilst selenium and tellurium offer an even wider range of derivatives. Thus, the following types of compounds are now well known ... 

OXYGEN, SULPHUR, SELENIUM, TELLURIUM, POLONIUM 367 Thiosulphates are numerous, fairly stable and usually very soluble in water... 

The distinctions between the system of equivalents ordinarily employed in this country, and the 2 volume notation adopted in this work, may be thus expressed. In the new system, the atomic weight of carbon is 12, of oxygen is 16, of sulphur is 32 and similarly with selenium and tellurium all the other atomic weights are unaltered. The atomic expressions for all bodies not containing carbon, oxygen, or sulphur, are unchanged thus, H, N, HCl, KI, NH, c. When in an atomic formula the atoms of carbon, oxygen, and sulphur, form even numbers, these numbers are halved thus, alcohol becomes G H O, ethyl... 

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