Barium atomic weight

Answer By the detection of elements of moderate atonic weight such as barium (atomic weight when U-235 is bombarded by slow neutrons. 

Aston EW (1932) The isotopic constitution and atomic weights of cesium, strontium, lithium, rubidium, barium, scandium and thallium. Proc Roy Soc A 134 571 Bach RO (ed) (1985) Lithium—Current Applications in Science, Medicine, and Technology. Wiley-Interscience, New York... 

In 1847 Sacc determined the atomic weight by several methods, of which only two proved of value, namely (i) pure selenium dioxide was reduced with ammonium hydrogen sulphite and the resulting selenium weighed (ii) barium selenite was calcined with sulphuric acid and the resulting barium sulphate weighed. The results were as follows 5... 

The element must be lanthanum—not cesium oi barium as seemed likely from the approximate atomic weight This is further confirmed by the formula which would have been Cs20 for Cs 01 BaO for Ba La/), agrees vwth the fact that La has a valence of +3... 

However, other scientists had also attempted to categorise the known elements. In 1817, Johann Dobereiner noticed that the atomic weight (now called atomic mass) of strontium fell midway between the weights of calcium and barium. These were elements which possessed similar chemical properties. They formed a triad of elements. Other triads were also discovered, composed of ... 

Tetrametaphosphates.—These salts are said to be formed when orthophosphates of metals of high atomic weight—silver, barium, lead—are heated with an excess of phosphoric acid at about 800° C.s The free acid, H4P4012, prepared by decomposing the silver salt with H2S, was rapidly hydrated to H4P207.8... 

That the elements [Hissessed relationships uf a different Hurt was shown soon after the establishment of Dalton s Atomic Theory. As early as 1817, Dnehereiner culled attention to the fact that strontium hud an atomic weight which was very close to the mean of the values for calcium and barium, while these three elements showed dose similarity in both physical mid chemical properties, Tatter he also showed that there are other triads in which the same general relationship exists, such... 

As his research advanced to the studies of gases and alkali metals, Bunsen recognized the importance of developing new methods to analyze and identify chemical substances. The importance of quantitative analysis was realized in the late eighteenth century. Chemists needed to probe further into a substance s composition in order to help explain the physical world. Bunsen recognized this need and worked to develop new instruments for this purpose. For example, he invented new types of galvanic and carbon-zinc electrochemical cells, or batteries, to isolate barium and sodium. He also constructed a new type of ice calorimeter that measured the volume, rather than the mass, of melted water. This allowed Brmsen to measure a metal s specific heat in order to find its atomic weight. 

Show that the result of determining the atomic weight of harium by precipitation of the chloride with silver nitrate is less influenced by experimental errors than the determination of the atomic weight of sodium in the same way. Assume that one part of silver as nitrate requires x parts of sodium (or barium) chloride for precipitation as silver chloride. Let a and b be the known atomio weights of silver and chlorine. Then, if y denotes the atomic weight of sodium, y+b a=x l or,y=ax-b a = (y + 6)/x. Differentiate,... 

If the atomic weight of barium y is determined by the precipitation of barium sulphate from barium chloride solutions, and a denotes the known atomic weight of chlorine, b the known combining weight of S04, then when x parts of barium chloride are converted into one part of barium sulphate,... 

The individual series here deviate from the general mean more than the magnitude of its probable error would lead us to suppose. The constant errors, in consequence, must be greater than the probable errors. In such a case as this, the computed probable error 0 0085 has no real meaning, and we can only conclude that the atomic weight of barium is, at its best, not known more accurately than to five units in the second decimal place.1... 

Physical and Chemical Properties Barium belongs to the alkaline earth elements, and has an atomic number 56 and a mean atomic weight of 137.33. Barium has seven stable isotopes Ba (71.70%), i Ba (11.23%), Ba (7.854%), Ba... 

Dobereiner went on to find two other groups of three elements exhibiting neat gradations of properties calcium, strontium, and barium and sulfur, selenium, and tellurium. In both groups the atomic weight of the element in the middle was about midway between those of the other two. Coincidence again ... 

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