Rubidium elemental properties

Chemical properties and spectroscopic data support the view that in the elements rubidium to xenon, atomic numbers 37-54, the 5s, 4d 5p levels fill up. This is best seen by reference to the modern periodic table p. (i). Note that at the end of the fifth period the n = 4 quantum level contains 18 electrons but still has a vacant set of 4/ orbitals. 

Rubidium [7440-17-7] Rb, is an alkali metal, ie, ia Group 1 (lA) of the Periodic Table. Its chemical and physical properties generally He between those of potassium (qv) and cesium (see Cesiumand cesium compounds Potassium compounds). Rubidium is the sixteenth most prevalent element ia the earth s cmst (1). Despite its abundance, it is usually widely dispersed and not found as a principal constituent ia any mineral. Rather it is usually associated with cesium. Most mbidium is obtained from lepidoHte [1317-64-2] an ore containing 2—4% mbidium oxide [18088-11-4]. LepidoHte is found ia Zimbabwe and at Bernic Lake, Canada. 

Physical Properties. Rubidium, a soft, ductile, silvery-white metal, is the fourth lightest metaUic element. Having a melting poiat of 39°C, it can be a Hquid at ambient temperatures. Table 1 Hsts certain physical properties. 

The alkali metals form a homogeneous group of extremely reactive elements which illustrate well the similarities and trends to be expected from the periodic classification, as discussed in Chapter 2. Their physical and chemical properties are readily interpreted in terms of their simple electronic configuration, ns, and for this reason they have been extensively studied by the full range of experimental and theoretical techniques. Compounds of sodium and potassium have been known from ancient times and both elements are essential for animal life. They are also major items of trade, commerce and chemical industry. Lithium was first recognized as a separate element at the beginning of the nineteenth eentury but did not assume major industrial importance until about 40 y ago. Rubidium and caesium are of considerable academic interest but so far have few industrial applications. Francium, the elusive element 87, has only fleeting existence in nature due to its very short radioactive half-life, and this delayed its discovery until 1939. 

A remarkable property of the atomic weights was discovered, in the sixties, independently by Lothar Meyer and Mendeleeff. They found that the elements could be arranged in rows in the order of their atomic weights so that similar elements would be found in the same columns. A modernised form of the Periodic Table will be found on pp. 106, 107. It will be noticed, for example, that the "alkali" metals, Lithium, Sodium, Rubidium and Caesium, which... 

The synthesis of HBr04 and rubidium and potassium salts was accomplished, using oxidation of bromate by XeF2 or (preferably) molecular fluorine in aqueous solution.19 Spectral studies20 show that the perbromate ion is tetrahedral in both the solid-state and aqueous solutions. The thermodynamic properties and thermal decomposition of individual salts are discussed under each element. A more general article on various properties of the perbromates was published by Herrell and Gayer.21... 

The existence of these different practices was not sufficient to create a discipline or subdiscipline of physical chemistry, but it showed the way. One definition of physical chemistry is that it is the application of the techniques and theories of physics to the study of chemical reactions, and the study of the interrelations of chemical and physical properties. That would mean that Faraday was a physical chemist when engaged in electrolytic researches. Other chemists devised other essentially physical instruments and applied them to chemical subjects. Robert Bunsen (1811—99) is best known today for the gas burner that bears his name, the Bunsen burner, a standard laboratory instrument. He also devised improved electrical batteries that enabled him to isolate new metals and to add to the list of elements. Bunsen and the physicist Gustav Kirchhoff (1824—87) invented a spectroscope to examine the colors of flames (see Chapter 13). They used it in chemical analysis, to detect minute quantities of elements. With it they discovered the metal cesium by the characteristic two blue lines in its spectrum and rubidium by its two red lines. We have seen how Van t Hoff and Le Bel used optical activity, the rotation of the plane of polarized light (detected by using a polarimeter) to identify optical or stereoisomers. Clearly there was a connection between physical and chemical properties. 

In properties potassium monosulphide resembles the sodium salt. The anhydrous substance forms small cubic octahedra, isomorphous with the monosulphide of rubidium, but not with that of caesium.1 At the laboratory temperature its density is 1-805.2 The heat of formation of the solid from its elements is 87-1 Cal.,3 and the heat of solution is 22-7 Cal. In dilute solution it has a strongly alkaline reaction, owing to almost complete hydrolysis to the hydroxide and primary sulphide. 

Fundamental atomic and physical properties of the alkali metals are given in Tables 1, 2, and 3. The elements are characterized by having electron configurations each with a single s orbital electron outside a noble gas core (see Table 1). Sodium and cesium are mononucUdic so that their relative atomic masses are known extremely accurately in effect, the same can be written for potassium and rubidium since their isotopes (of which there are three and two, respectively) have... 

The ammonium ion NH4+ has a tetrahedral structure and is slightly acidic (p/fa = 9.25). If no strong hydrogen bonds are present, like in NH4F, the properties of ammonium salts, for example, the solubility and the structure, are similar to the corresponding potassium and rubidium salts. The reasons are similar ionic radii of the aimnonium (143 pm), potassium (137 pm), and rubidium ions (148 pm). The oxonium salts H30+X , which have lower melting points, are also similar to the ammonium salts. The similar properties of element-hydrogen compounds have been rationalized by the hydride displacement law shown in Table 12. 

The elements of the first group, lithium, sodium, potassium, rubidium, and cesium, are soft, silvery-white metals with great chemical reactivity. These elements are called the alkali metals. These metals are excellent conductors of electricity. Some of their physical properties are given in Table 91. It can be seen from the table that they melt at low temperatures—four of the five metals melt below the boiling point of water. The metals lithium, sodium, and potassium are lighter than water. 

Pure elements at room temperature and atmospheric pressure can be solids, liquids, or gases. Some elements are colorless. Others, like the ones shown in Figure 1, are colored. Despite the differences between elements, groups of elements share certain properties. For example, the elements lithium, sodium, potassium, rubidium, and cesium can combine with chlorine in a 1 1 ratio to form LiCl, NaCl, KCl, RbCl, and CsCl. All of these compounds are white solids that dissolve in water to form solutions that conduct electricity. 

Sodium and oxygen combine to form sodium oxide, which has the formula Na20. Use the periodic table to predict the formulas of the oxides of potassium, rubidium, and cesium. What periodic property of the elements are you using ... 

The most serious defect in the system, especially in its usefulness in the laboratory, is that similar elements are sometimes in remote positions, while dissimilar elements are brought close together. These difficulties are most pronounced in qualitative analysis, in which the solubilities of salts are of prime importance. As illustrations of this defect it may be observed that copper and mercury, silver and thallium, barium and lead, have many similar properties which are not suggested by their positions ixi the table. On the other hand we might expect gold and caesium, rubidium aud silver, and manganese and chlorine to resemble each other much more closely than they do. It is obvious, however, that no table could possibly show all the resemblances and contrasts of each dement, and a, detailed study of each of these elements justifies in a measure its usual position in the table. 

Rubidium gas has become important in the study of an exotic state of matter called a Bose-Einstein condensate. This state, first predicted in 1924 by Indian physicist Satyendra Nath Bose, was not observed until 1995. Many laboratories now produce these cooled clouds of atoms, mostly using gases of alkali elements, which have appropriate spin and magnetic properties. 

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