Mendeleev beryllium

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 ... 

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... 

Indicate the position of beryllium, magnesium, calcium, strontium, and barium in Mendeleev s periodic table of the elements, the electron configurations and size of their atoms, and their oxidation states. 

In 1885 the issue was finally conclusively settled in favor of Mendeleev by measurements of the specific heat of beryllium at elevated temperatures. These experiments pointed to an atomic weight of 9.0, in reasonable agreement with Dulong and Petit s law and supported the di-valency of the element (Humpidge, 1885). Above all else, Mendeleev persisted in the belief that beryllium lies in group II because of his faith in the validity of the periodic law, which he believed was essentially a feature of the transcendental elements. All else was rationalized around this central tenet. 

The Russian chemist, Dmitri Mendeleev, was a professor of chemistry at the University of St. Petersburg when he developed a periodic table of the elements. Mendeleev was studying the properties of the elements and realized that the chemical and physical properties of the elements repeated in an orderly way when he organized the elements according to increasing atomic mass. For example, beryllium resembled magnesium, and boron resembled aluminum. Patterns of repeated properties began to appear. 

Using his table, Mendeleev also was able to correct several values for atomic masses. For example, the original atomic mass of 76 for indium was based on the assumption that indium oxide had the formula InO. This atomic mass placed indium, which has metallic properties, among the nonmetals. Mendeleev assumed the atomic mass was probably incorrect and proposed that the formula of indium oxide was really 10203. Based on this correct formula, indium has an atomic mass of approximately 113, placing the element among the metals. Mendeleev also corrected the atomic masses of beryllium and uranium. 

Mendeleev tackled matters from the direction of valence (see page 110). He noted that the earlier elements in the list showed a progressive change in valence. That is, hydrogen had a valence of 1, lithium of 1, beryllium of 2, boron of 3, carbon of 4, nitrogen of 3, sulfur of 2, fluorine of 1, sodium of 1, magnesium of 2, aluminum of 3, silicon of 4, phosphorus of 3, oxygen of 2, chlorine of 1, and so on. 

The placement of the metal beryllium provided one of the most severe tests for Mendeleev s system. Its case proved to be historically significant because it involved a controversy that lasted a considerable period of time, ending with the complete vindication of Mendeleev s position. The question was whether the element should be assigned a valence of 2 or 3, which would affect its atomic weight and thus would in turn govern the position it took in the periodic table. 

For fttUer details of Mendeleev on magnesium and beryllium, see J.R. Smith, Persistence and Periodicity, unpublished Ph.D. thesis. University of London, 1975. 

Newlands law (law of octaves) The observation that, when the elements are arranged in order of increasing relative atomic mass, there is a similarity between members that are eight elements apart (inclusive). For example, fithium has similarities to sodium, beryllium to magnesium, and so on. Newlands discovered this relationship in 1863 before the announcement of Mendeleev s famous periodic law (1869). It is now recognized that Newlands law arises from there being eight members in each short period. It is named for the British chemist John Newlands (1837-98). 

Chemists had long known that groups of elements have similar properties. In 1869 Dmitri Mendeleev found that when the elements were arranged in a particular way, they fell into columns, with elements in the same column displaying similar properties.Thus, Mendeleev placed beryllium, calcium, strontium, and barium in one column. Now, with the Curies discovery, radium was added to this column. 

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