Noble gases chemical properties

The isolation and identification of 4 radioactive elements in minute amounts took place at the turn of the century, and in each case the insight provided by the periodic classification into the predicted chemical properties of these elements proved invaluable. Marie Curie identified polonium in 1898 and, later in the same year working with Pierre Curie, isolated radium. Actinium followed in 1899 (A. Debierne) and the heaviest noble gas, radon, in 1900 (F. E. Dorn). Details will be found in later chapters which also recount the discoveries made in the present century of protactinium (O. Hahn and Lise Meitner, 1917), hafnium (D. Coster and G. von Hevesey, 1923), rhenium (W. Noddack, Ida Tacke and O. Berg, 1925), technetium (C. Perrier and E. Segre, 1937), francium (Marguerite Percy, 1939) and promethium (J. A. Marinsky, L. E. Glendenin and C. D. Coryell, 1945). 

Most of the U-series nuclides are metals. Five of them belong to the actinide family corresponding to the filling of the internal orbitals while the orbitals 7s are filled. A sixth, Ra is an alkali earth and shares some chemical properties with other alkali earths, particularly the heavier ones (Sr and Ba), while a seventh, Rn, is a noble gas. The filling of the orbitals prescribes the possible oxidation states of these elements. Their preferred oxidation state is obtained when the electronic configuration is that of the closest rare gas (Rn). 

Radon is a noble gas and is therefore not readily ionized or chemically reactive. Its properties in terrestrial material will be controlled by its solubility in melt and fluid as well as its diffusion coefficients. Compared with the lighter noble gases, Rn diffuses more slowly and has a lower solubility in water. It will also more readily adsorb onto surface that the lighter rare gases. It can, however be lost by degassing in magmatic systems (Condomines et al. 2003). More information about the behavior of Rn can be found in Ivanovich and Harmon (1992). 

Due to the expected high volatility of elements with atomic numbers 112 to 118 in the elemental state [104], see also Chapters 2 and 6, gas phase chemical studies will play an important role in investigating the chemical properties of the newly discovered superheavy elements. An interesting question is, if e.g. elements 112 and 114 are indeed relatively inert gases (similar to a noble gas) [105] due to closed s2 and p /22 shells, respectively, or if they retain some metallic character and are thus adsorbed quite well on certain metal surfaces, see Chapter 6, Part II, Section 3.2. Extrapolations by B. Eichler et al. [106] point to Pd or Cu as ideal surfaces for the adsorption of superheavy elements. 

The bulk properties of macroscopic crystals cannot be affected drastically by the difference which exists between the structure of the interior and that of a surface film which is approximately 10,000 atoms deep. However, even for macroscopic crystals, rate phenomena such as modification changes which are initiated within the surface are likely to be influenced by the environment, which would include molecules which are conventionally described as physically adsorbed. Apparently it is not generally understood that even the presence of a noble gas can affect the chemical reactivity of solids. Brunauer (3) explained that in principle physical adsorption of molecules should affect the solid in the same manner as chemisorption. As action and reaction are equal, chemisorption may have a stronger effect on both the solid and the adsorbed molecule. 

Tie chemical properties of an element depend primarily on its number of valence electrons in its atoms. The noble gas elements, for example, all have similar chemical properties because the outermost energy levels of their atoms are completely filled. The chemical properties of ions also depend on the number of valence electrons. Any ion with a complete outermost energy level will have chemical properties similar to those of the noble gas elements. The fluoride ion (F ), for example, has a total of ten electrons, eight of which fill its outermost energy level. F has chemical properties, therefore, similar to those of the noble gas neon. 

From the chemical point of view, the most direct and dramatic consequence of the )3-decay is undoubtedly the sudden change of chemical identity undergone by the radioactive atom, which drastically affects all its properties, including the ability to form, or maintain, chemical bonds. If the radioactive atom is chemically combined, the change of its atomic number is often sufficient to cause the disruption of the molecule, particularly when the nuclide formed from the decay is a chemically inert, noble gas atom. Other important chemical consequences follow directly from the intrinsic physical characteristics of the nuclear transformation. 

In the first place, as described in the earlier Section, the j3-decay changes the atomic number, and therefore the valency and all the chemical properties of the radioactive atom. This change alone is often sufficient to cause disruption of the molecule, particularly in those cases where the product of the radioactive decay is a noble gas atom. In the second place, an initially neutral molecule will become positively charged, as a result of the increased nuclear charge, and all the sources of electronic excitation discussed for the decay of isolated atoms will of course affect the molecule as well. 

Elements 104 to 112 are transition elements (6d s to 6d s ). For the first half of these elements high oxidation states are predicted. Elements 112 and 114 are of special interest, because of the relativistic effects of the filled 7s level of 112 and the filled 7pyj sublevel of 114, which give these elements a noble character. The formation of the 7pi/2 sublevel is also expected to influence the oxidation states of elements 115 to 117. With increasing atomic number, the energy differenee between the pi/2 and P3/2 sublevels increases with the result that only the P3/2 eleetrons will be available as valenee electrons. Element 118 should be a noble gas but, due to its low ionization energy, compounds should easily be formed in which this element has the oxidation state IV or VI. Some chemical properties predieted for elements 104 to 121 are summarized in Table 14.7. 

The relatively recent development of a new class of chemical laser based on the formation of noble gas-halide exciplexes and producing coherent radiation at a number of different u.v. wavelengths has been quickly adopted by both kineticists and spectroscopists. This Section brings together a few studies which have appeared in the past year dealing with the properties (i.e., kinetics, photophysics, etc.) of complexes important in the noble gas-htilide systems. The numerous articles that have appeared giving details of performance characteristics of such lasers (and their improvement) are deemed to be beyond the scope of this Report and are not included. However, the proceedings of two recent conferences on lasers have been published in which much of this information can be found. 

The first element in the periodic able, hydrogen, is a reactive substance which forms a great many compounds. The c hemistry of hydrogen is discussed in the following chapter. Helium, the second element, is much different it is a gas with the very striking chemical property that it forms no chemical compounds whatever, but exists only in the free state. Its atoms will not even combine witfi one another to form polyatomic molecules, but remain as separate atoms,in the gas, which is hence described as containing monatomic molecules. Because of its property of remaining aloof from other elements it is called a noble gas. 

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