Boron atomic weight

The results may be calculated as boron (atomic weight 10.811) or, by multi-... 

Boron has 2 stable naturally occurring isotopes and the variability of their concentration (particularly the difference between borates from California (low in °B) and Turkey (high in °B) prevents the atomic weight of boron being quoted more precisely than 10.811(7) (p. 17). Each isotope has a nuclear spin (Table 6.1) and this has proved particularly valuable in nmr spectroscopy, especially for The great... 

By the middle of the nineteenth century more than 60 elements were known with new ones continuing to be discovered. For each of these elements, chemists attempted to determine its atomic weight, density, specific heat, and other properties. The result was a collection of facts, which lacked rational order, Mendeleev noticed that if the elements were arranged by their atomic weights, then valencies and other properties tended to recur periodically. However, there were gaps in the pattern and in a paper of 1871 Mendeleev asserted that these corresponded to elements that existed but had not yet been discovered. He named three of these elements eka-aluminium, eka-boron and eka-silicon and gave detailed descriptions of their properties. The reaction of the scientific world was sceptical. But then in 1874 Lecoq de Boisbaudran found an... 

The decision to add an unoccupied orbital with a large weighting factor to the prototype carbene in the case of BA and an occupied one for XA is easily made. The boron atom introduces a low energy unoccupied orbital and the oxygen a high energy occupied one into the aromatic n-system. The choice is less clear for FL and its derivatives. Providence, however, provides the same conclusion from either choice. 

Mendeleev arranged the elements into seven groups. Lithium (atomic weight 7) was followed by beryllium (9), boron (11), carbon (12), nitrogen (14), oxygen (16), and fluorine (19). The next element in order of atomic weight was sodium (23), which had properties similar to those of lithium. Therefore, Mendeleev pinned the card for sodium under that for lithium. Six more cards were placed in the second row, ending with chlorine under fluorine. He continued in... 

Mendeleev observed that there were some gaps in his table, empty spaces to which no element was assigned. He concluded that these represented elements that had not yet been discovered. For example, there was a gap under boron, so Mendeleev concluded that it must be an unknown element with properties like boron. He named it eka-boron ( eka is Sanskrit for the numeral one). Similarly, there were gaps under aluminum and silicon. Mendeleev called these missing elements eka-aluminum and eka-silicon. The positions of the missing elements in his table allowed him to estimate their atomic weights and also to describe their chemical and physical properties accurately. 

The discovery of gallium was followed by the discovery of scandium (Mendeleev s eka-boron) in 1879 and of germanium (eka-sili-con) in 1886. The new elements had the approximate atomic weights and properties that Mendeleev had predicted. The scientific world was astonished. It is probably safe to say that before Mendeleev s predictions were confirmed, no chemist would have believed that the properties of unknown elements could be predicted with such accuracy. 

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. ... 

Out of Russia came the patriarchal voice of a prophet of chemistry. There is an element as yet undiscovered. I have named it eka-aluminum. By properties similar to those of the metal aluminum you shall identify it. Seek it, and it will be found. Startling as was this prophecy, the sage of Russia was not through. He predicted another element resembling the element boron. He was even bold enough to state its atomic weight. And before that voice was stilled, it foretold the discovery of a third element whose physical and chemical properties were thoroughly described. No man, not even the Russian himself, had beheld these unknown substances. 

The atomic heats are therefore 5-83, 5-74 and 6-26 over the three ranges of temperature (1), (2), (3). There is a slight deviation from Dulong and Petit s law 9 at the lower temperatures, in the same sense as that met with in the case of the elements carbon, boron and silicon. But although phosphorus has a relatively low atomic weight, it also has a low melting-point, and the atomic heat as usual assumes the normal value at temperatures near the melting-point. 

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