Solid Noble Gases

Would you expect the surface energies of the Noble-gas solids to be greater than, about the same as, or smaller than those of ionic crystals Explain. 

Harl, J. and Kresse, G. (2008) Cohesive energie curves for noble gas solids calculated by adiabatic connection fluctuation-dissipation theory. Phys. Rev. B, 77, 045135-1-045136-8. 

In any close-packed arrangement, each interior atom is surrounded by 12 nearest-neighbor atoms. The number of nearest-neighbor atoms of an atom is called its coordination number. Thinking of atoms as hard spheres, one can calculate that the spheres occupy 74% of the space of the crystal. There is no way of packing identical spheres so that an atom has a coordination number greater than 12 or the spheres occupy more than 74% of the space of the crystal. All the noble-gas solids have cubic close-packed crystals except helium, which has a hexagonal close-packed crystal. 

In TOF-SARS [9], a low-keV, monoenergetic, mass-selected, pulsed noble gas ion beam is focused onto a sample surface. The velocity distributions of scattered and recoiled particles are measured by standard TOF methods. A chaimel electron multiplier is used to detect fast (>800 eV) neutrals and ions. This type of detector has a small acceptance solid angle. A fixed angle is used between the pulsed ion beam and detector directions with respect to the sample as shown in figure Bl.23.4. The sample has to be rotated to measure ion scattering... 

Shirley E L 1998 Many-body effects on bandwidths in ionic, noble gas, and molecular solids Phys. Rev. B 58 9579-83... 

Pure anhydrous aluminium chloride is a white solid at room temperature. It is composed of double molecules in which a chlorine atom attached to one aluminium atom donates a pair of electrons to the neighbouring aluminium atom thus giving each aluminium the electronic configuration of a noble gas. By doing so each aluminium takes up an approximately tetrahedral arrangement (p. 41). It is not surprising that electron pair donors are able to split the dimer to form adducts, and ether, for example, forms the adduct. 

The O oxidation state is known in vanadium hexacarbonyl. V(CO)(,. a blue-green, sublimable solid. In the molecule VfCO), if each CO molecule is assumed to donate two electrons to the vanadium atom, the latter is still one electron short of the next noble gas configuration (krypton) the compound is therefore paramagnetic, and is easily reduced to form [VfCO, )]. giving it the... 

Chromium forms a white solid, hexacarhonyl, Cr(CO)j, with the chromium in formal oxidation state 0 the structure is octahedral, and if each CO molecule donates two electrons, the chromium attains the noble gas structure. Many complexes are known where one or more of the carbon monoxide ligands are replaced by other groups of ions, for example [CrfCOlsI] . 

Standard texts may be consulted on the topic of diffusion ia solids (6,12,13). Some generalizations, however, are possible. No noble gas permeates a metal. Metals are, however, permeated readily by hydrogen. Stainless steel, for example, can be permeated by hydrogen from concentrations likely ia air. 

In 1962 the report, TID-14844 was published presenting analysis and assumptions coneeming the behavior of containment (essentially Hazard State 2). The TID report postulated the release of all of the noble gas, 50% of the iodine, and 1% of the radioactive solids to the containment. In addition, TBD-14844 provided assumptions for containment leakage (the TMI-2 containment is intact) and for atmo.spheric transport of the fission products. These results form the basis for Regulatory... 

Xe is comparable to, that of molecular oxygen (1175kJmol for O2 -> 02 + e )- He quickly proceeded to show that deep-red PtFe vapour spontaneously oxidized Xe to produce an orange-yellow solid and announced this in a brief note/ Within a few months Xep4 and Xep2 had been synthesized in other laboratories/ Noble-gas chemistry had begun. 

Until about 40 years ago, these elements were referred to as "inert gases" they were believed to be entirely unreactive toward other substances. In 1962 Neil Bartlett, a 29-year-old chemist at the University of British Columbia, shook up the world of chemistry by preparing the first noble-gas compound. In the course of his research on platinum-fluorine compounds, he isolated a reddish solid that he showed to be 02+(PtFB-). Bartlett realized that the ionization energy of Xe (1170 kJ/mol) is virtually identical to that of the 02 molecule (1165 kJ/mol). This encouraged him to attempt to make the analogous compound XePtF6. His success opened up a new era in noble-gas chemistry. 

The chemistry of xenon is much more extensive than that of any other noble gas. Only one binary compound of krypton. KrF2, has been prepared. It is a colorless solid that decomposes at room temperature. The chemistry of radon is difficult to study because all its isotopes are radioactive. Indeed, the radiation given off is so intense that it decomposes any reagent added to radon in an attempt to bring about a reaction. 

Stable noble gas compounds are restricted to those of xenon. Most of these compounds involve bonds between xenon and the most electronegative elements, fluorine and oxygen. More exotic compounds containing Xe—S, Xe—H, and Xe—C bonds can be formed under carefully controlled conditions, for example in solid matrices at liquid nitrogen temperature. The three Lewis structures below are examples of these compounds in which the xenon atom has a steric munber of 5 and trigonal bipyramidal electron group geometry. 

In low energy ion scattering (LEIS, also called ion scattering spectroscopy, ISS) a beam of noble gas ions with energy of a few keV scatters elastically from a solid sur-... 

A final note must be made about a common problem that has plagued many kinetic treatments of reactive intermediate chemistry at low temperatures. Most observations of QMT in reactive intermediates have been in solid matrices at cryogenic temperatures. Routinely, reactive intermediates are prepared for spectroscopy by photolyses of precursors imbedded in glassy organic or noble gas (or N2) solids. The low temperatures and inert surroundings generally inhibit inter- and intramolecular reactions sufficiently to allow spectroscopic measurements on conventional and convenient timescales. It is under such conditions, where overbarrier reactions are diminished, that QMT effects become most pronounced. 

The application of matrix isolation to organometallic chemistry has been extensively described elsewhere (4,5,6,7). Two methods have generally been employed. In the first, based on G.C. Pimentel s original development, the solid matrix environment is a frozen noble gas - usually Ar - at 10-20K and the unstable fragment is generated either by photolysis of a parent molecule already trapped in the matrix, or by cocondensation from the gas phase. In the... 

The nitrogen complex had already been synthesized in a solid matrix, but its decomposition kinetics and its further photolysis could be studied only in solution. The liquid noble gas technique is superior to the solid matrix technique, especially for the synthesis of multiple substituted chromium carbonyl nitrogen complexes. Their IR spectra were extremely complex in matrices, due to "site splittings" which arise when different molecules are trapped in different matrix environments /18/. 

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