Noble Gas Atoms

PI, PIS Penning ionization [116, 118] Auger deexcitation of metastable noble-gas atoms 4. ... 

To date there is no evidence that sodium forms any chloride other than NaCl indeed the electronic theory of valency predicts that Na" and CU, with their noble gas configurations, are likely to be the most stable ionic species. However, since some noble gas atoms can lose electrons to form cations (p. 354) we cannot rely fully on this theory. We therefore need to examine the evidence provided by energetic data. Let us consider the formation of a number of possible ionic compounds and first, the formation of sodium dichloride , NaCl2. The energy diagram for the formation of this hypothetical compound follows the pattern of that for NaCl but an additional endothermic step is added for the second ionisation energy of sodium. The lattice energy is calculated on the assumption that the compound is ionic and that Na is comparable in size with Mg ". The data are summarised below (standard enthalpies in kJ) ... 

What a storyi Fullerenes formed during the ex plosion of a star travel through interstellar space as passengers on a comet or asteroid that eventually smashes into Earth Some of the fullerenes carry pas sengers themselves—atoms of helium and argon from the dying star The fullerenes and the noble gas atoms silently wait for 251 million years to tell us where they came from and what happened when they got here... 

Interatomic potentials began with empirical formulations (empirical in the sense that analytical calculations based on them... no computers were being used yet... gave reasonable agreement with experiments). The most famous of these was the Lennard-Jones (1924) potential for noble gas atoms these were essentially van der Waals interactions. Another is the Weber potential for covalent interactions between silicon atoms (Stillinger and Weber 1985) to take into account the directed covalent bonds, interactions between three atoms have to be considered. This potential is well-tested and provides a good description of both the crystalline and... 

It has one adjustable parameter which was chosen so that the sum of the LDA and Becke exchange terms accurately reproduce the exchange energies of six noble gas atoms. 

Atoms that are dose to a noble gas (Group 18) in the periodic table form ions that contain the same number of electrons as the neighboring noble-gas atom. 

This is reasonable noble-gas atoms must have an extremely stable electronic structure, because they are so unreactive. Other atoms might be expected to acquire noble-gas electronic structures by losing or gaining electrons. 

As pointed out in Chapter 2, elements close to a noble gas in the periodic table form ions that have the same number of electrons as the noble-gas atom. This means that these ions have noble-gas electron configurations. Thus the three elements preceding neon (N, O, and F) and the three elements following neon (Na, Mg, and Al) all form ions with the neon configuration, is22s22p6. The three nonmetal atoms achieve this structure by gaining electrons to form anions ... 

According to this model, it would seem that for an atom to form a covalent bond, it must have an unpaired electron. Indeed, the number of bonds formed by an atom should be determined by its number of unpaired electrons. Because hydrogen has an unpaired electron, an H atom should form one covalent bond, as indeed it does. The same holds for the F atom, which forms only one bond. The noble-gas atoms He and Ne, which have no unpaired electrons, should not form bonds at all they don t... 

Strictly speaking, the noble gases are "atomic" rether than molecular. However, like molecules, the noble-gas atoms are attracted to one another by dispersion forces. 

The pattern of ion formation by main-group dements can be summarized by a single rule for atoms toward the left or right of the periodic table, atoms lose or gain electrons until they have the same number of electrons as the nearest noble-gas atom. Thus, magnesium loses two electrons and becomes Mg2+, which has the same number of electrons as an atom of neon. Selenium gains two electrons and becomes Se2+, which has the same number of electrons as krypton. 

FIGURE 2.2 When a main-group metal atom forms a cation, it loses its valence s-and p-electrons and acquires the electron configuration of the preceding noble-gas atom. The heavier atoms in Croups 1 S/lll and 14/IV retain their complete subshells of d-electrons. 

FIGURE 15.25 The colors of this fluorescent lighting art hv Tom vnl noble-gas atoms. Neon is responsible for the red light i > li... 

The Distribution of Spherons in Layers.—Several theoretical and empirical arguments indicate that the nature of spheron-spheron interactions is not such as to limit the ligancy of a spheron to a fixed value, but that, instead, maximum stability is achieved when each spheron ligates about itself the maximum number of neighbors aggregates of spherons, like aggregates of argonon (noble-gas) atoms or metal atoms, assume a closest-packed structure. 

The noble gases are the only elements that exist naturally as individual atoms. Electron configurations make it clear why noble gas atoms prefer to remain as single atoms. Each noble gas has a filled shell configuration 1 for He and for the others. All electrons are paired, and there are no vacant... 

Ghanty, T.K. (2005) Insertion of noble-gas atom (Kr and Xe) into noble-metal molecules (AuF and AuOH) Are they stable Journal of Chemical Physics, 123, 074323-1-074323-7. 

The formulas for the metal carbonyls are determined by the number of pairs of electrons needed by the metal to reach the number of electrons in the next noble gas atom. Thus, the stable carbonyl with nickel contains four CO molecules, that with iron contains five, and that with chromium contains six. The bonding in these complexes will be discussed in more detail in Chapter 16. 

Janssens et al. [38, 40] used photoemission of adsorbed noble gases to measure the electrostatic surface potential on the potassium-promoted (111) surface of rhodium, to estimate the range that is influenced by the promoter. As explained in Chapter 3, UPS of adsorbed Xe measures the local work function, or, equivalently, the electrostatic potential of adsorption sites. The idea of using Kr and Ar in addition to Xe was that by using probe atoms of different sizes one could vary the distance between the potassium and the noble gas atom. Provided the interpretation in terms of Expression (3-13) is permitted, and this is a point the authors checked [38], one thus obtains information about the variation of the electrostatic potential around potassium promoter atoms. 

A special type of TM ligands are the noble gas atoms argon, krypton, and xenon [61]. Although they are weak Lewis bases, TM complexes M(CO)sNg with M = Cr, Mo, W and Ng = Ar, Kr and Xe have been experimentally investigated in the gas phase as well as in the liquid phase and in supercritical C02 [62, 63], The M-Ng BDEs were estimated with... 

Non-ionizing electron-neutral interactions create electronically excited neutrals. The ionization reactions occurring when electronically excited neutrals, e.g., noble gas atoms A, collide with ground state species, e.g., some molecule M, can be divided into two classes. [21] The first process is Penning ionization (Eq. 2.6), [22] the second is associative ionization which is also known as the Hombeck-Molnar process (Eq. 2.7). [23]... 

Penning ionization occurs with the (trace) gas M having an ionization energy lower than the energy of the metastable state of the excited (noble gas) atoms A. The above ionization processes have also been employed to construct mass spectrometer ion sources. [21,24] However, Penning ionization sources never escaped the realm of academic research to find widespread analytical application. 

As described earlier, high pressure cells have been developed for the use of noble gases as solvents for IR spectroscopic studies, either at low temperature, or at ambient temperature where the supercritical phase exists. A particular focus of this work was the study of reactive complexes containing coordinated noble gas atoms or molecular H2, the latter being particularly relevant to hydrogenation reactions. 

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