Crystalline solids ionic structures

Dinitrogeri pentoxide is the anhydride of nitric acid and is prepared by removing water from pure nitric acid by means of phosphorus (V) oxide. It is a crystalline solid having the ionic structure of (N02) (N03) , nitronium nitrate (the nitronium ion is mentioned later). It decomposes above 273 K, thus ... 

The starting point for the synthesis of xenon compounds is the preparation of xenon difluoride, XeF2, and xenon tetrafluoride, XeF4, by heating a mixture of the elements to 400°C at 6 atm. At higher pressures, fluorination proceeds as far as xenon hexafluoride, XeFfi. All three fluorides are crystalline solids (Fig. 15.27). In the gas phase, all are molecular compounds. Solid xenon hexafluoride, however, is ionic, with a complex structure consisting of XeF< + cations bridged by F anions. 

These electrostatic attractions act in all directions. Thus, ionic crystalline solids consist of metal ions are surrounded by non-metal ions and non-metal ions surrounded by metal ions. Therefore, ionic solids do not have a molecular structure. 

With hydrogen, the alkali metals form the mono-hydrides MeH, having salt-like properties and a partially ionic, Me H, NaCl-type structure. They are colourless crystalline solids having a fairly negative AH of formation. The mono-hydrides react with water. They may be prepared from hydrogen and the metal (heated at 700-800°C for Li, 350-400°C for the others) or through the reaction of hydrogen with the alkali mono-oxide, nitride, etc. 

Rather specific structural features appear to be necessary for high ionic conductivity in crystalline solids, and as a result it may seem surprising that glasses can support high ionic conductivity. For example, a Li" conductivity of 0.16mScm at 25 °C for a glass with the composition... 

This opening chapter has introduced many of the principles and ideas that lie behind a discussion of the crystalline solid state. We have discussed in detail the structure of a number of important ionic crystal structures and shown how they can be linked to a simple view of ions as hard spheres that pack together as closely as possible, but can also be viewed as the linking of octahedra or tetrahedra in various ways. Taking these ideas further, we have investigated the size of these ions in terms of their radii, and... 

Like infrared spectrometry, Raman spectrometry is a method of determining modes of molecular motion, especially the vibrations, and their use in analysis is based on the specificity of these vibrations. The methods are predominantly applicable to die qualitative and quantitative analysis of covalently bonded molecules rather than to ionic structures. Nevertheless, they can give information about the lattice structure of ionic molecules in the crystalline state and about the internal covalent structure of complex ions and the ligand structure of coordination compounds both in the solid state and in solution. 

The nature of the bonds between the structural units of crystalline solids impart other physical properties to these solids. Metals are good conductors of electricity because metallic bonds allow a free flow of electrons. Covalent network, molecular, and ionic solids do not conduct electricity because their bonds do not provide for mobile electrons. Remember, however, that ionic solids in a water solution have free electrons and are good conductors of electricity. Metallic solids are malleable and ductile covalent network solids are brittle and hard. These differences in physical properties are caused by the chemical bonds between the units It is all in the bonds ... 

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