Tellurium atomic weight

He also points out several times the important evidential role played by the success of Mendeleev s contrapredictions —the corrections of atomic weight values previously assigned to already known elements—such as beryllium, uranium and tellurium—so that they fitted into his table smoothly. And indeed the most elaborate statement of Brush s general conclusion seems to be the following ... 

The realization that the better ordering criterion is atomic number rather than atomic weight invites us to consider triads of atomic numbers. This reveals a most remarkable fact, namely that —50% of all conceivable triads on a conventional periodic table are in fact exact. For example, the elements sulfur, selenium, and tellurium have atomic numbers of 16, 34, and 52, respectively, thus showing that the atomic number of the middle of these three... 

The silver white, shiny, metal-like semiconductor is considered a semimetal. The atomic weight is greater than that of the following neighbor (iodine), because tellurium isotopes are neutron-rich (compare Ar/K). Its main use is in alloys, as the addition of small amounts considerably improves properties such as hardness and corrosion resistance. New applications of tellurium include optoelectronics (lasers), electrical resistors, thermoelectric elements (a current gives rise to a temperature gradient), photocopier drums, infrared cameras, and solar cells. Tellurium accelerates the vulcanization of rubber. 

Lee DC, Halliday AN (1995) Precise determinations of the isotopic compositions and atomic weights of molybdenum, tellurium, tin and tungsten using ICP magnetic-sector multiple collector mass-spectrometry. Int J Mass Spectr Ion Proc 146 35-46... 

In the previous section, you reviewed the historical determination of atomic weights. Notice that the elements also seem to be arranged in order of increasing atomic weight. But there are several exceptions. Compare the atomic weight of tellurium (Te) to iodine (I). (See Figure 1-3-)... 

Consider the proper placement of tellurium and iodine in the periodic table, as shown in Figure 1-3. Te has the heavier atomic weight. The chemical properties of tellurium are like those of selenium because both are semi-metallic elements that form compounds like those of sulfur. Iodine resembles bromine because these elements are nonmetallic halogens that form compounds like those of chlorine. Therefore, the order in the table cannot be based solely on atomic weight. 

After commenting on the discovery of gallium, scandium, and germanium (eka-aluminum, eka-boron, and eka-silicon), D. I. Mendeleev had written in 1891, I foresee some more new elements, but not with the same certitude as before. I shall give one example, and yet I do not see it quite distinctly (7). He had then proceeded to describe an undiscovered dvi tellurium with an atomic weight of about 212. Since polonium resembles tellurium and has an estimated atomic weight of about 210, it is probably the realization of Mendeleev s dvi tellurium. ... 

Thus Moseley s series is almost the same as Mendeleev s series of increasing atomic weights. When, however, the elements are arranged, not according to their atomic weights, but according to their atomic numbers (Moseley numbers), the discrepancies between argon and potassium and between iodine and tellurium disappear (10). 

The tendency to form complexes increases with the atomic weight of the element. Tellurium resembles iodine in entering into the formation of iso- and hetero-polyacids of the basic formula Te(OH)6. 

The atomic weight of tellurium was determined for the first time by Berzelius in 1812, the value obtained being 129-2. The tellurium used, however, was impure, a fact only recognised in 1817.2 In 1833 Berzelius repeated his determinations,3 converting tellurium into its dioxide this time he obtained the value 4 128-34. 

Dudley and Bowers,1 having first obtained pure tellurium by fractional precipitation with hydrazine hydrochloride,2 synthesised the tetra-bromide and obtained a mean value of 127-479 for the atomic weight. 

Gut bier and Wagenknecht in 1905 carried out a series of determinations based on the reduction of tellurium dioxide to the metal.3 The reduction was effected by two distinct methods, but the results in both eases were practically the same. In the first series of experiments the dioxide was mixed with silver and powdered quartz and reduced in a current of hydrogen. In the second series the reduction was effected by means of hydrazine hydrochloride. The mean value for the atomic weight from both series of determinations was 127-62. 

Lenher 6 determined the atomic weight of tellurium by decomposing weighed amounts of potassium telluribromide, K2TeBr6, by means of chlorine and hydrogen chloride, and weighing the potassium chloride which remained. Using tellurium ores from three different sources, the oxide obtained was converted into the double bromide by the action of hydrobromic acid and potassium bromide the telluribromide formed was crystallised repeatedly from water. As a mean of sixteen concordant experiments Lenher obtained the value 127-55. 

Tellurium is a mixture of three isotopes,5 the mass-numbers of which are 128, 180 and 126. The intensities of the first two are about equal and double that of the third, so that it would seem probable that the mean atomic weight is at least as high as 128. The discrepancy between this conclusion and the actual values obtained remains to be explained. Tellurium is unique in that all its mass-numbers form members of iso-baric pairs, these being shared by xenon, the element of next higher even atomic number. The atomic number of tellurium is 52. 

Selenium and tellurium arc generally considered rare elements and are not found in abundance each, however, has a claim to special interest. The peculiar electrical properties of selenium appeal especially to the physical chemist, but the compounds of this element are of growing importance, especially in their application to the glass industry. Both selenium and tellurium offer attractive fields for research. In the case of tellurium, owing to what had been considered an erroneous value for the atomic weight, the very considerable amount of work done in the past has been too much confined to one direction interest in the chemistry of tellurium appears now to be widening, however. 

Dmitri Mendeleyev (1834-1907), a Russian scientist and creator of the modern periodic table, discovered that if elements were lined up according to atomic weights and arranged in rows of 2, 8, 18, and 32, atoms with similar chemical and physical properties appeared in the same column. However, there were some exceptions. Argon and potassium were out of place. So were iodine and tellurium. Mendeleyev thought his relative weights were incorrect. 

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