Argon crystal lattice

Kazakov, G. A., and G. I. Teplinsky On argon intrusion into the crystal lattice of glauconite. Geochemistry (UdSSR) 2, 148 (1966). 

Figure 2. The minimum potential energy, tm, of a helium atom interacting with the 100 face of an argon crystal is plotted as a function of the position of the helium atom relative to the surface lattice...

The differential cross sections of argon and neon have been measured by using refinements of the modulated molecular-beam technique. From these measurements the intermolecular potentials were found. These potentials differ significantly from the Lennard-Jones potential. The neon and argon potentials have different shapes and are not related by any simple scaling factor. The macroscopic properties have been calculated and are in reasonable agreement with experiment. The face-centered cubic structure was found to be the most stable crystal lattice for neon. The effect of the argon potential on the critical properties and saturation pressures is also discussed. 

The dipotassium salt is stable in solution or as a crystalline solid but it explodes on the least contact with oxygen or moisture and turns brown even in an atmosphere of nitrogen or argon [28,30]. The salts are thermodynamically very stable this is attributed partly to the ten ir-electron system but more especially to the large negative crystal lattice energy [33]. 

Each sodium ion is surrounded by six chloride ions and each chloride ion is surrounded by six sodium ions. The coordination numbers of both ions are six. In the formation of NaQ, the sodium atom loses its valency electron (3s ) to the chlorine atom (3s 3p ) so that Na and Cl" have the electronic configurations of neon and argon, respectively, in accordance with the octet rule (discussed in Section 5.3). Because the electron attachment enthalpy of chlorine (-355 kJ mol" ) does not provide compensation for the enthalpy used to ionize the sodium atom (500 kJ mol" ), the stability of the compound is produced by the attractive forces operating between the oppositely charged ions in a crystal lattice. 

Fig. 1. The crystal structure of a hydroquinone clathrate according to Palin and Powell. 8 The balls inside the transparent spheres represent argon atoms encaged in the cavities formed by the two interpenetrating lattices, (photograph kindly supplied by Dr. Powell).

Generally, increasing molecular size, heavier atoms and more polar bonds contribute to an increased lattice energy of a molecular crystal. Typical values are argon 7.7 kJ mol-1 krypton 11.1 kJmol-1 organic compounds 50 to 150 kJ mol-1. 

Radon forms a series of clathrate compounds (inclusion compounds) similar to those of argon, krypton, and xenon. These can be prepared by mixing trace amounts of radon with macro amounts of host substances and allowing the mixtures to crystallize. No chemical bonds are formed the radon is merely trapped in the lattice of surrounding atoms it therefore escapes when the host crystal melts or dissolves. Compounds prepared in this manner include radon hydrate, Rn 6H20 (Nikitin, 1936) radon-phenol clathrate, Rn 3C H 0H (Nikitin and Kovalskaya, 1952) radon-p-chlorophenol clathrate, Rn 3p-ClC H 0H (Nikitin and Ioffe, 1952) and radon-p-cresol clathrate, Rn bp-CH C H OH (Trofimov and Kazankin, 1966). Radon has also been reported to co-crystallize with sulfur dioxide, carbon dioxide, hydrogen chloride, and hydrogen sulfide (Nikitin, 1939). 

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