Discovery and Isolation of the Elements

The discovery of the alkali metals superimposed on the plot of the number of known elements versus time. 

Davy did not stay a pneumatic chemist very long. In 1800, just before the young Davy arrived in London, Alessandro Volta announced his construction of the first chemical battery (a voltaic pile ) capable of producing a sustained and predictable current. As soon as word of this battery came to Davy, he built one and—you guessed it—immediately tested it by administering a series of shocks on himself Immediately, Davy realized that his future lay in electrochemistry, not pneumatic chemistry. 

Humphiy Davy ca. 1803. S. Freeman s engraving of Davy taken from a portrait of Davy made in 1803, taken from the collection of June Z. Fullmer, author of The Young Humphry Davy American Philosophical Society, Philadelphia (2000). 

For a dozen years he regularly produced a series of immensely popular lectures on the latest discoveries in and applications of chemistry. Active in research, he discovered six elements in two years (1807-1808), conclusively disproved Lavoisier s hypothesis that oxygen was present in all acids (1810), and discovered and launched Michael Faraday into a stellar chemistry career. In 1812, he was knighted and in 1815 invented the coal miner s safety lamp that saved many lives. 

His work in isolating the alkali metals (and the alkaline earth metals) started in the early 1800s when he built a very large voltaic pile and experimented with passing electrical currents through a variety of materials including molten samples of potash and soda ash, what we know today to be potassium and sodium carbonates. 

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In the remaining sections of this chapter chemical comparisons between silicon and carbon are developed. Since all organosilicon chemistry essentially starts with the element, the discussion begins with the discovery and isolation of the element and some of the simple chemistry of silicon that was described in the eighteenth century. The basic starting materials for organosilicon chemistry were available in the past century, but their... 

The first two sections of this chapter are the usual ones on (1) the discovery and isolation of the elements and (2) the application of the network to group chemistry. The third section, necessitated by the great ability of sulfur to catenate, concentrates on the allotropes and compounds that involve element-to-element bonds. Next is a short section on the relatively new and potentially useful sulfur nitrides. The reactions and compounds of practical importance in the fourth section include sodium-sulfur batteries, the photoelectric properties of selenium and tellurium, and the most important commercial chemical in the world, sulfuric acid. The selected topic in depth is the production, effects, and possible control of acid rain. 

The history of these elements and their few compounds dominates this chapter. We start with the usual treatment of the discovery and isolation of the elements, followed by a much shorter than normal section on periodic properties and the network. Given that the actual chemistry of this group is dominated by xenon, the third section is devoted almost entirely to the preparation, structure, and reactions of its compounds. A short section on the practical importance of the elements is followed by the selected topic in depth, the carcinogenic threat of radon. 

Although there have been numerous refinements to Mendeleev s early tabulation, fortified by the discovery and isolation of several elements then unknown the fundamental principles of the matrix are the same. The conventional table is shown in the upper right in Fig. 2, The information also can be presented in polar fashion as shown in Fig. 2. It is interesting to note that as one proceeds clockwise around the circle the atomic numbers appear consecutively and that 18 sectors of the circle become the bases for families or groups of elements. 

Today, the most advanced chemical principles are based on quantum mechanics and have led to remarkable developments in spectroscopy, materials synthesis, etc. All of these developments have aided the discovery and isolation of new elements, compounds, and molecules. We briefly outline a few of these developments in the following sections. 

Our research at Berkeley has resulted in the discovery of element 94, demonstration of the slow neutron fissiona-bility of its isotope 94239, discovery and demonstration of the slow neutron fissionability of U23 3, spontaneous fission measurements on these isotopes, discovery of 93237, isolation of and nuclear measurements on U23, study of the chemical properties and methods of chemical separation of element 94, demonstration of the presence of small concentrations of 94 in nature and much related information. 

Discovery of the Periodic Table was rendered possible only after four decisive prerequisites had been achieved. These were (i) the abandonment of the metaphysical and occult notions of elements that typified the alchemical era (ii) the adoption of a modern and workable definition of an element (iii) the development of analytical chemical techniques for the isolation of the elements and determination of their properties and (iv) the devising of a means of associating each element with a characteristic natural number. The Periodic Table made its appearance on cue almost as soon as these preconditions had been fulfilled... 

Let us close with a reveahng bit of doggerel, illustrating how the concept of the atom was changing before chemists veiy eyes. The author is eminent British chemist William Ramsay, best known for his role in the discovery and isolation of most of the noble gas elements, for which he was awarded the 1904 Nobel Prize in Chemistry. He wrote these verses for his 1902 lab dinner. 

The recognition of the similarity in chemical properties between the actinide and lanthanide elements was an important contributing factor in the synthesis and isolation of the transcurium elements. Most of the chemical identification was carried out by eluting the elements from columns of cation exchange resin. The pattern of the elution behavior from the resin bed of the lanthanide elements made it possible to predict with good accuracy the expected elution position for a new actinide element (Fig. 16.7). This technique constituted the most definitive chemical evidence in the discovery experiments for the elements from atomic numbers 97 through 101. More recently these conclusions have been confirmed by spectroscopy. 

The reason for this surprising lag between initial discovery and the beginnings of a serious study and exploitation of the rare earths lies in the facts of their mineralogical origin and their great chemical similarity leading to enormous difficulties in separation and isolation of the individual elements. These issues are discussed in the following section. 

The isotope produced was the 20-hour 255Fm. During 1953 and early 1954, while discovery of elements 99 and 100 was withheld from publication for security reasons, a group from the Nobel Institute of Physics in Stockholm bombarded 238U with 160 ions, and isolated a 30-min alpha-emitter, which they ascribed to 250-100, without claiming discovery of the element. This isotope has since been identified positively, and the 30-min half-life confirmed. 

Vanadium was first discovered in 1801 by del Rio while he was examining a lead ore obtained from Zimapan, Mexico. The ore contained a new element and, because of the red color imparted to its salts on heating, it was named erythronium (redness). The identification of the element vanadium did not occur until 1830 when it was isolated from cast iron processed from an ore from mines near Taberg, Sweden. It was given the name vanadium after Vanadis, the Norse goddess of beauty. Shordy after this discovery, vanadium was shown to be identical to the erythronium that del Rio had found several years eadier. 

All six possible diatomic compounds between F, Cl, Br and I are known. Indeed, ICl was first made (independently) by J. L. Gay Lussac and H. Davy in 1813-4 soon after the isolation of the parent halogens themselves, and its existence led J. von Liebig to miss the discovery of the new element bromine, which has similar properties (p. 794). The compounds vary considerably in thermal stability CIF is extremely robust ICl and IBr are moderately stable and can be obtained in very pure crystalline form at room temperature BrCl readily dissociates reversibly into its... 

Marie Curie (Paris) discovery of the elements radium and polonium, the isolation of radium, and the study of the nature and compounds of this remarkable element. 

In the 1800s chemists searched for new elements by fractionating the oxides of rare-earths. Carl Gustaf Mosander s experiments indicated that pure ceria ores were actually contaminated with oxides of lanthanum, a new element. Mosander also fractionated the oxides of yttria into two new elements, erbium and terbium. In 1878 J. Louis Soret (1827—1890) and Marc Delafontaine (1837-1911), through spectroscopic analysis, found evidence of the element holmium, but it was contaminated by the rare-earth dysprosia. Since they could not isolate it and were unable to separate holmium as a pure rare-earth, they did not receive credit for its discovery. 

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