The noble gases

The reaction was carried out with the knowledge that oxygen reacts with the very strong oxidizing agent, PtF6. 

One reason that this reaction is so interesting is that the ionization potential for the oxygen molecule is 1177 kj/mol (compared to that of a hydrogen atom, which is 1312 kj/mol) and that for Xe is 

Helium has long been related to nuclear chemistry because of the formation of alpha particles (a = 4He2+) during the decay of heavy nuclei, an example of which is 

An a particle can abstract two electrons from some other atom or molecule (and given the extremely high ionization potential of helium, the highest of any atom, it would be difficult to prevent it) to become a helium atom. Helium also is a constituent in stars as a result of the fusion reaction 

From 235U 22SRa — 222Rn + 4He2+ [ty2 = 3.825 days) (15.228) 

These elements were unknown when Mendeleef constructed his periodic table, and are often said to constitute Group O . How ever, a more logical classification would be in Group VIII . 

The increase in atomic radius (in this group, the actual radius of the/ree atom). 

Element Atomic number Outer electrons Atomic radius (nm) m.p. (K) b.p. (K) 1st ionisation energy (kJ mol  

The increase in melting point and boiling point, and the very narrow liquid range. 

The large ionisation energies, as expected for atoms with com plete quantum levels. 

The preferred method of disposal of radioactive krypton isotopes, after being separated from other volatile fission products, is by dumping at sea as the compressed gas, confined in steel cylinders. According to a report by Bryant and Jones the cumulative quantities of Kr and in the environment by the year 2000 are such that these nuclides will pose no significant health problem. 

The first directly observed Xe I =, natural abundance 26.4%) n.m.r. spectra of xenon compounds have been reported by Seppelt and Rupp the key results are depicted in Table 1 and are discussed in later sections. Other workers have used pulsed F.T. n.m.r. spectroscopy to obtain Xe chemical shifts in the gaseous phase at lower pressures than was previously possible. Accurate vapour-pressure measurements for Ar, Kr, and Xe in their normal liquid ranges have been determined and thermodynamic quantities calculated from them.  

A new method for the preparation of Krp2 has been reported by Slivnik et aC It involves the irradiation of a liquefied mixture of fluorine and krypton with near-u.v. light at -196 °C and, compared with other methods, it may be used for larger quantities, e.g. 4.7 g of Krp2 after 48 h irradiation. Russian workers have recorded the absorption spectrum of gaseous Krp2 and have hence calculated the oscillator strengths.  

The Xe n.m.r. ehemieal shifts of some xenon(ii) derivatives are shown in Table 1 in this oxidation state the shifts fail within the range -2952 to -3508 p.p.m. (relative to xenon), which is intermediate between the range for both xenon-(iv) and -(vi) species and for xenon itself. The observation of J( Xe—F) as well as of /( Xc— Te) coupling constants is of spectroscopic interest. 

SbF5 2XeF2,TaFs. The same workers also obtained evidence for the 

The Group 8A(18) elements are helium (He, the second most abundant element in the universe), neon (Ne), argon (Ar, which makes up about 0.93% of Earth s atmosphere), krypton (Kr), xenon (Xe), and radioactive radon (Rn). Only the last three form compounds [Group 8A(18) Family Portrait]. 

The observation of XeCl in the gas phase at 10 Torr has been claimed. The ion was generated in a conventional ion-cyclotron resonance spectrometer by means of the reaction COCl + Xe XeCl + CO. The dissociation energy of XeCl into Xe and Cl was estimated to be less than 10kcalmol. However, ab initio electronic-structure calculations on the lowest and 11 states of XeF suggest that this is not a chemically bound species in the gas phase. 

An oxidation method for removing radon from gas mixtures by means of the reaction with liquid BrFg has been tested using samples containing amounts of the order of 0.2 pCi 1 of Rn. The possibility of purifying air in uranium mines with BrFs and other oxidizing agents was discussed. 

The molecular structure of the unknown argon(ii) fluoride has been predicted from that of the formally analogous MesPFg the Ar— F bond length 

Elemental xenon can be oxidized by Cl2F+AsF but not by CIF itself. The overall reaction is  

The successful gas chromatographic determination of XeF2 on a column filled with a porous polymer has bron described. The absorption spectra of gaseous and solid 3 F2 measured in the 50—160eV region show the continuous contribution from the F and Xe components, and furthermore, a 

The structure and bonding of KrClF, a van der Waals molecule, have been determined by molecular beam electric resonance spectroscopy the atomic arrangement is Kr—GIF, analogous to that in ArClF, with the Kr—Cl distance 3.39 A. 

spectrum of XeFj has been measured accurately in the photon energy range 6—35 eV, and assignments are consistent with the ionization potentials given in the literature/ Ab initio theoretical methods have been used to study the electronic structure of XeFj the bonding was found to conform quite closely with Coulson s model, viz. FXc F F Xe F. Liebman has discussed the evidence for the existence of the XeF ion. 

Additional Xen.m.r. spectroscopic data have been obtained by the F.T. technique on a range of complexes a striking correlation was revealed between the Xe shift and the F shift for the terminal fluorine(s) of FXeZ (Z = F, SO3F, FM0OF4, or FWOF4) and of (FXe)2Z (Z = S03F or F ). 

The X-ray structure of XeF2,2SbF5 has now been refined and the geometry around the XeF cation has been confirmed. In addition, there is evidence for a weak F-bridge (Xe— F = 3.06 A), which is also reflected in the distortions of the Sb2F7i group. Measurements of the heat of hydrolysis of this adduct were also reported, and a standard heat of formation (—705 kcalmor ) was inferred. 

Zemva and J. Slivnik, J. Inorg. Nuclear Chem., Supplement, 1976, 173. 

The noble gases (Table 2.6) are uniform in their inability to bind a positron. The stability of the system of a positron and an excited helium atom in its metastable 23S state is interesting. This state has an optical lifetime of about 20 ns. The excited electron in a 2s-orbital is far enough from the nucleus to attract and bind a positron. Similar states of other atoms must be common. 

Ps02 1959 2.3 Positron lifetime spectra in liquid oxygen [62] gas-phase quenching data with a Born cycle interpretation [63]. 

OPs 1969 2.2(5) Positron lifetime data and thermodynamic argument based on a proposed mechanism involving the oxidation of Ps by H+ [64]. 

PsF 1969 2.9(5) Interpretation of positron lifetime spectra in liquid C6H6 vs C6H5F [64]. 

PsH 1968 2.35 11) °) Extrapolation to zero density for a sequence of alkali hydride crystals [69]. 

Because my co-workers at that time (March 23,1962) were still not sufficiently experienced to help me with the glassblowing and the preparation and purification ofPtFg [platinum hexafluoride] necessary for the experiment, I was not ready to carry it out until about 7 p.m. on that Friday. When I broke the seal between the red PtFg gas and the colorless xenon gas, there was an immediate interaction, causing an orange-yellow solid to precipitate. At once I tried to find someone with whom to share the exciting finding, but it appeared that everyone had left for dinner  

Neil Bartlett in Fluorine Chemistry, at the Millennium Banks, R. E. ed., Elsevier Amsterdam, 2000, p. 39. 

Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main-Group Elements, First Edition. Abhik Ghosh and Steffen Berg. 

A ucENT Communication dcKribed the compound dioxygeoyl hexalluofaplitiMta(v), Oi+PlF, which is ronned when moleculv oxygen is oxidised by pUlimim hexafluoride vapour. Since the first ionisation potential of molecular oxygen, 12-2 ev, is comparable with that of xenon, 12-0 ev, it appeared that xenon might also be oxidised by the hexafluoride. 

Tbe composition of the evolved gas was eslabiished by mass-spcelromeiric analysis. 

The closed-shell electronic structures of the noble-gas atoms are completely stable, as shown by the high ionization potentials, especially of the lighter members (Table 17-1). The elements are all low-boiling gases whose physical properties vary fairly systematically with atomic number. The boiling point of helium is the lowest of any known substance. The boiling points and heats of vaporization increase monotonically with increasing atomic number. 

Outer shell configuration Atomic number 1st IP (eV) Normal b.p., °K Aii/vap (kJ mol-1) % by volume in the atmosphere Promotion energy (eV), ns2np6-+ ns2nps(n+ l)s 

The heats of vaporization are measures of the work that must be done to overcome interatomic attractive forces. Since there are no ordinary electron-pair interactions between noble-gas atoms, these weak forces must be of the van der Waals or London type such forces are proportional to the polarizability and inversely proportional to the ionization potentials of the atoms they increase therefore as the size and diffuseness of the electron clouds increase. 

The noble gases occur as minor constituents of the atmosphere (Table 17-1). Helium is also found as a component (up to 7%) in certain natural hydrocarbon gases in the United States. This helium undoubtedly originated from decay of radioactive elements in rocks, and certain radioactive minerals contain occluded helium which can be released on heating. All isotopes of radon are radioactive and are occasionally given specific names (e.g., actinon, thoron) derived from their source in the radioactive decay series 222Rn is normally obtained by pumping off the gas from radium chloride solutions. Ne, Ar, Kr and Xe are obtainable as products of fractionation of liquid air. 

The trapping of Ar, Kr and Xe in clathrate compounds has been discussed in Chapter 5. 

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Inert gases A semi-obsolete name for the noble gases. ... 

Except for the n = 1 quantum level the maximum number of electrons in the outermost quantum level ofany period isalwayseight. At this point the element concerned is one of the noble gases (Chapter 12). 

When Mendeleef devised his periodic table the noble gases were unknown. Strictly, their properties indicate that they form a group beyond the halogens. Mendeleef had already used Group VIIl to describe his transitional triads and the noble gases were therefore placed in a new Group O. 

Industrially, elemental nitrogen is extracted from the air by the fractional distillation of liquid air from which carbon dioxide and water have been removed. The major fractions are nitrogen, b.p. 77 K and oxygen, b.p. 90 K, together with smaller quantities of the noble gases. 

It is one of the "noble" gases. It is characterized by its brilliant green and orange spectral lines. 

The noble gases are mostly unreactive. In some instances, they act mostly as a place holder to fill a cavity. For dynamical studies of the bulk gas phase or liquid-phase noble gases, hard-sphere or soft-sphere models work rather well. 

Closed shell electron configuration (Sections 1 1 and 116) Stable electron configuration in which all the lowest energy orbitals of an atom (in the case of the noble gases) an ion (e g Na" ) or a molecule (e g benzene) are filled... 

It follows from this that the excited configurations of C and Si in Equation (7.10) give P, P, D, D, and terms. It follows also that the noble gases, in which all occupied orbitals are filled, have only 5 terms arising from their ground configurations. 

In the case of atoms UPS is unlikely to produce information which is not available from other sources. In addition many materials have such low vapour pressures that their UPS spectra may be recorded only at high temperatures. The noble gases, mercury and, to some extent, the alkali metals are exceptions but we will consider here only the specttum of argon. 

Table 11 illustrates the known closed proton and neutron shells and the predicted closed nuclear shells (shown in parentheses) that might be important in stabilising the superheavy elements. Included by way of analogy are the long-known closed electron shells observed in the buildup of the electronic stmcture of atoms. These correspond to the noble gases, and the extra stabiUty of these closed shells is reflected in the relatively small chemical reactivity of these elements. The predicted (in parentheses) closed electronic stmctures occur at Z = 118 and Z = 168. 

Fluorine forms very reactive halogen fluorides. Reaction of CI2 and F2 at elevated temperatures can produce GIF, CIF, or CIF 3 be obtained from the reaction of Br2 and F2. These halogen fluorides react with all nonmetals, except for the noble gases, N2, and O2 (5). Fluorine also forms a class of compounds known as hypofluorites, eg, CF OF (6). Fluorine peroxide [7783-44-0], O2F2, has also been reported (6). 

Iodine forms compounds with all the elements except sulfur, selenium, and the noble gases. It reacts only indirectly with carbon, nitrogen, oxygen, and some noble metals such as platinum. 

Tritium differs from the noble gases. Tritium is very reactive and readily combines to form water. The voloxidation process, which controls the point at which the oxidation occurs and recovers the resulting tritiated water, has been developed. As of this writing it has not yet been used. 

Properties. Uranium metal is a dense, bright silvery, ductile, and malleable metal. Uranium is highly electropositive, resembling magnesium, and tarnishes rapidly on exposure to air. Even a poHshed surface becomes coated with a dark-colored oxide layer in a short time upon exposure to air. At elevated temperatures, uranium metal reacts with most common metals and refractories. Finely divided uranium reacts, even at room temperature, with all components of the atmosphere except the noble gases. The silvery luster of freshly cleaned uranium metal is rapidly converted first to a golden yellow, and then to a black oxide—nitride film within three to four days. Powdered uranium is usually pyrophoric, an important safety consideration in the machining of uranium parts. The corrosion characteristics of uranium have been discussed in detail (28). 

The dominant internal event accident scenarios were used in conjunction with conservative source terms (100% of the core melts, releasing 100% of the noble gases, 100% nf iodine and cesium, and 1% solids), and )ecific meteorological data to estimate e consequences to be well below the lOCFRlOO siting guidelines. 

Radon A radioactive element, the heaviest of the noble gases, formed by the radioactive decay of radium. 

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