Density alkaline earth metals

One current limitation of orbital-free DFT is that since only the total density is calculated, there is no way to identify contributions from electronic states of a certain angular momentum character /. This identification is exploited in non-local pseudopotentials so that electrons of different / character see different potentials, considerably improving the quality of these pseudopotentials. The orbital-free metliods thus are limited to local pseudopotentials, connecting the quality of their results to the quality of tlie available local potentials. Good local pseudopotentials are available for the alkali metals, the alkaline earth metals and aluminium [100. 101] and methods exist for obtaining them for other atoms (see section VI.2 of [97]). 

The interstitial hydrides of transition metals differ from the salt-like hydrides of the alkali and alkaline-earth metals MH and MH2, as can be seen from their densities. While the latter have higher densities than the metals, the transition metal hydrides have expanded metal lattices. Furthermore, the transition metal hydrides exhibit metallic luster and are semiconducting. Alkali metal hydrides have NaCl structure MgH2 has rutile structure. 

Metal hydrides containing transition metal (TM)-hydrogen complexes, with the transition metal in a formally low oxidation state, are of fundamental interest for clarifying how an electron-rich metal atom can be stabilized without access to the conventional mechanism for relieving the electron density by back-donation to suitable ligand orbitals. By reacting electropositive alkali or alkaline earth metals ( -elements) with group 7, 8, 9, and 10 transition metals in... 

Some physical and chemical properties of the alkaline earth metals are shown in Table II. It can be seen that beryllium is significantly different from the elements below it in the periodic table in most respects. The fact that the density of beryllium is greater than that of magnesium is perhaps surprising, but can be understood by noting that magnesium is both a more massive and a larger atom. The density of beryllium is to be compared to that of iron (7.9 g cm-3), titanium (4.5 g cm-3), and aluminum (2.7 g cm-3). 

Exchange in zeolites of alkali, alkaline earth, transition metal ions and small organic ammonium ions, has been reviewed (111), and in general, the exchange is characterized by small AG values comparable to those found in clay minerals. Althoufft identical selectivity orders for alkali and alkaline earth metal ions are obtained, as in montmorillonite, the opposite variation of AG with charge density is found. 

Table 5.8. Alkaline earth metals crystal structures, lattice parameters of their allotropes and calculated densities. When not differently indicated the allotropic transformations refer to room pressure.

Concerning the nature of Lewis basic sites, little work has been done to establish general rules and models, except for alkaline earth metal oxides and zeolites. With respect to the former, i.e., the nature of oxygen Lewis basic sites on alkaline earth metal oxide catalysts, a charge-density model predicts that the strength of the sites decreases in the order > OH > H2O > H30. ... 

Another factor which determines the presence of minerals at certain depths is the tendency to combine with others or affinity of minerals and elements. Noble gases hardly react with other elements and will, because of their low densities, consequently end up in the atmosphere. Relatively light elements (alkaline and alkaline earth metals) with a strong affinity for oxygen are found in the silicate schaal. Heavy elements which are bound to sulphur or oxgen are situated in the sulphide /oxide scale, or even deeper in the nickel/iron scale. 

There are some relationships between a metal s position on the periodic table and the physical properties studied. Magnesium and calcium, alkaline earth metals, are not very malleable or ductile. They have low densities 1.74 g/cm3 and 1.55 g/cm3, respectively. All of the other metals tested are transition metals. They exhibit a wide range of physical properties. Copper and silver are in the same family. They are both quite ductile and malleable. They have fairly high densities. 

If a solution containing approximately 4 mole percent sodium in ammonia is cooled below -42°C (231 K) a remarkable liquid-liquid phase separation occurs (33, 155). The solution physically separates into two distinct layers—a low-density, bronze metallic phase that floats out on top of a more dense, less concentrated dark-blue phase. The first experimental observation of this striking phenomenon in sodium-ammonia solutions was made by Kraus (109, 110) in 1907 more recent studies have mapped out the phase coexistence curves for a variety of alkali and alkaline earth metals in liquid ammonia, and these are delineated and discussed elsewhere (164). 

In 1956 it was found that europium and ytterbium dissolve in liquid ammonia with the characteristic deep blue color known for the alkali and alkaline earth metals [36-40]. This behavior arises from the low density and high volatility of those metals compared to the other lanthanide elements [41]. Samarium, which normally also occurs in the divalent oxidation state, does not dissolve under... 

The method most generally applied to the isolation of lithium is based on the decomposition of the fused chloride by electrolysis, modifications in practical details having been introduced by various experimenters. Bunsen and Matthiessen1 passed the current from six Bunsen cells through the fused chloride contained in a porcelain crucible, with a carbon rod as anode and an iron wire as cathode. Troost employed a similar method. Guntz2 mixed lithium chloride with potassium chloride, but his product contained 1-3 per cent, of potassium. His current was 10 amperes at 20 volts, with a cathode of iron wire 3-4 mm. in diameter. Borchers3 added chlorides of other alkali-metals and alkaline-earth-metals and a small proportion of ammonium chloride, and employed a current density of 10 amperes per 100 sq. cm. Tucker 4 electrolyzed the chloride without the addition of other material. 

The alkaline earth metals have great practical importance. Calcium and magnesium ions are essential for human life. Calcium is found primarily in the structural minerals composing bones and teeth. Magnesium (as the Mg2+ ion) plays a vital role in metabolism and in muscle functions. Because magnesium metal has a relatively low density and displays moderate strength, it is a useful structural material, especially if alloyed with aluminum. 

This effect is also found for the bandwidth of the 0(2p) bands for the alkaline earth metal oxides which, at the LDA level of theory, decrease down the group from a calculated value of 4.44eV (MgO) to 1.83eV (BaO). This is partly due to the increase in lattice parameter, which spaces the O " ions more widely in BaO than in MgO. However, in addition, it is found that the outermost valence electrons for the metal ions interact more strongly with the 0(2p) states in BaO than in MgO, giving more localization of the electron density at O " and so a smaller anion in BaO [50]. 

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