Compounds of krypton and radon

Radon is oxidized by halogen fluorides (e.g. CIF, CIF3) to the non-volatile Rnp2 the latter is reduced by H2 at 770 K, 

Christe (2001) Angewandte Chemie International Edition, vol. 40, p. 1419 - An overview of recent developments A renaissance in noble gas chemistry . 

Frenking and D. Creme (1990) Structure and Bonding, vol. 73, p. 17 - A review The chemistry of the noble gas elements helium, neon and argon . 

Greenwood and A. Earnshaw (1997) Chemistry of the Elements, 2nd edn, Butterworth-Heinemann, Oxford -Chapter 18 covers the noble gases in detail. 

Holloway and E.G. Hope (1999) Advances in Inorganic Chemistry, vol. 46, p. 51 - A review of recent developments in noble gas chemistry. 

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Stable compounds of krypton and radon have also been synthesized. Helium, neon, and argon form no known stable compounds, but they have been observed to form compounds for short periods of time. 

Occurrence, extraction and uses Physical properties Compounds of xenon Compounds of krypton and radon... 

The product is a volatile, colorless solid (Figure 22.52). Since then, a number of noble-gas compounds have been prepared that typically involve bonds to the highly electronegative elements fluorine and oxygen. Most of these are compounds of xenon (see Table 22.12), but a few are compounds of krypton and radon. Recently, an argon compound, HArF, was synthesized as well as compounds of CUO bonded to Ne, Ar, Kr, and Xe. All of these recent compounds were synthesized at very low temperatures. 

The elements helium, neon, argon, krypton, xenon, and radon—known as the noble gases—almost always have monatomic molecules. Their atoms are not combined with atoms of other elements or with other atoms like themselves. Prior to 1962, no compounds of these elements were known. (Since 1962, some compounds of krypton, xenon, and radon have been prepared.) Why are these elements so stable, while the elements with atomic numbers 1 less or 1 more are so reactive The answer lies in the electronic structures of their atoms. The electrons in atoms are arranged in shells, as described in Sec. 3.6. (A more detailed account of electronic structure will be presented in Chap. 17.)... 

Since the discovery of the first noble gas compound, Xe PtF (Bartlett, 1962), a number of compounds of krypton, xenon, and radon have been prepared. Xenon has been shown to have a very rich chemistry, encompassing simple fluorides, XeF2> XeF, and XeF oxides, XeO and XeO oxyf luorides, XeOF2> XeOF, and Xe02 2 perxenates perchlorates fluorosulfates and many adducts with Lewis acids and bases (Bartlett and Sladky, 1973). Krypton compounds are less stable than xenon compounds, hence only about a dozen have been prepared KrF and derivatives of KrF2> such as KrF+SbF, KrF+VF, and KrF+Ta2F11. The chemistry of radon has been studied by radioactive tracer methods, since there are no stable isotopes of this element, and it has been deduced that radon also forms a difluoride and several complex salts. In this paper, some of the methods of preparation and properties of radon compounds are described. For further information concerning the chemistry, the reader is referred to a recent review (Stein, 1983). 

Trofimov, A. M. and Kazankin, Yu. N., Clathrate Compounds of p-Cresol with Noble Gases. II. Compound of p-Cresol with Krypton and Radon, Radiokhim. 8 720-723 (1966). 

The Group 18 elements in the periodic table are currently called the noble gases. In the past, however, they were referred to as the inert gases. They were believed to be totally unreactive. Scientists have found that this is not true. Some of them can be made to react with reactive elements, such as fluorine, under the proper conditions. In 1962, the synthesis of the first compound that contained a noble gas was reported. Since then, a number of noble gas compounds have been prepared, mostly from xenon. A few compounds of krypton, radon, and argon have also been prepared. 

Because the noble gases have filled s and p valence orbitals, they are not expected to be chemically reactive. In fact, for many years these elements were called inert gases because of this supposed inability to form any compounds. However, in the early 1960s several compounds of krypton, xenon, and radon were synthesized. For example, a team at the Argonne National Laboratory produced the stable colorless compound xenon tetrafluoride (XeF4). Predict its structure and determine whether it has a dipole moment. 

In the past 35 years other xenon compounds have been prepared. Examples are Xe04 (explosive), XeOF4, XeOF2, and, XeCUF . These compounds contain discrete molecules with covalent bonds between the xenon atom and the other atoms. A few compounds of krypton, such as KrF2 and KrF4, have also been observed. The structures of several known xenon compounds are shown in Fig. 19.27. Radon also has been shown to form compounds similar to those of xenon and krypton. 

The closed-shell configuration of noble gas atoms Ng does not prevent formation of compounds, either as even, positive oxidation states of xenon, isosteric with iodine complexes (and to a smaller extent by krypton and radon) or functioning as Lewis bases. In condensed matter, Ar, Kr, and Xe form distinct NgCr(CO)j and ArCi(NN)5 complexes. Gaseous noble gas molecular ions, especially HeX and ArX, numerous organo-helium cations, and some neon-containing cations are calculated to be quite stable, and several of them are indeed detected in mass-spectra. The history of Ng chemistry and its relations with the Periodic Table, atomic spectra, and ionization energies, are discussed. 

Prior to 1962 the rare gases were frequently called inert gases as no chemical compounds were known (there were a few clathrates and hydrates ), but the realization that the ionization potential of xenon was sufficiently low to be accessible to chemical reaction led to the preparation of several fluorides, oxides, oxyfluorides, and a hexafluoroplatinate of xenon. Several unstable krypton and radon compounds have been synthesized. 

The Group VIIIA elements exist as gases consisting of uncombined atoms. For a long time these elements were thought to be chemically inert, because no compounds were known. Then, in the early 1960s several compounds of xenon were prepared. Now compounds are also known for krypton and radon. These elements are known as the noble gases because of their relative unreactivity. 

In our discussions of bonding, we pointed out the relative stability of the electron configurations of the Group VIIIA noble gases. For many years, it was thought that because the atoms of these elements had completed octets, Ihe noble gases would be completely unreactive. Consequently, these elements were known as inert gases. Compounds of krypton, xenon, and radon have since been prepared, however, so (he term is not quite appropriate. 

Note that the reaction products with entries in Table 19.1 are much abbreviated compared with the analogous tables of earlier groups. Only xenon and krypton react with fluorine to produce fluorides. Therefore, instead of following the usual format of describing the hydrides, oxides, hydroxides, and halides of these elements (most of which do not exist), we adopt a historical description of the synthesis of xenon compounds and then briefly expand the discussion to include the small number of examples drawn from krypton and radon chemistry. 

Other xenon halides include the dichloride, the tetrachloride, and the dibromide, but these are not particularly stable. Solutions of xenon trioxide, called xenic acid, are excellent oxidizing agents, as is the octahedral perxenate anion, XeOg. Krypton difluoride, a few nitrogen compounds of both xenon and krypton, and radon difluoride have also been prepared but are not well-characterized. 

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