NaCl Crystalline Structure

Turning next to an ionic crystal, where the ions may be regarded as spheres, the total volume of the crystal is equal to the volumes of these spheres, together with the appropriate amount of void space between the spheres. To take the simplest case, it is convenient to discuss a set of substances, all of which have the same crystalline structure—for example, the 17 alkali halide crystals that have the NaCl 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. 

Nitrides and Oxynitrides. Crystalline films of NbN and Nb Nj have been prepared. Electron-diffraction studies showed that the former has a NaCl-type structure and the latter is isomorphous with Ti405 and Ta Nj. " The phase 0-TaN, 0 has been prepared by nitriding Ta metal powder with ammonia gas at 850—1200°C. Although it could not be obtained pure, the phase was characterized by X-ray diffraction studies. The free energy of formation of TajNj has been determined as -272 42 kJ mol and that of TaO, 05N0.95 as -396 21 kJ moP. ... 

It should be mentioned that, of the other first-row transition metal oxides crystallizing with the NaCl structure, none has been found to superconduct down to 2.5 K. Some of these oxides undergo magnetic ordering at low temperature and most behave as semiconductors at all temperatures. These would include MnO, FeO, CoO, and NiO. Studies performed on CuO, which has a different crystalline structure, showed only semiconducting behavior to very low temperatures (1.9 K). 

An ionically bonded molecule (NaCl). (a) A sodium atom (Na) can donate the one electron in its valence shell to a chlorine atom (Cl), which has seven electrons in its outermost shell. The resulting ions (Na+ and CP) bond to form the compound sodium chloride (NaCl). The octet rule has been satisfied, (b) The ions that constitute NaCl form a regular crystalline structure in the solid state. 

Table 4 reports characterization results for the samples obtained by Route B. The solids consisted, in all cases, of pure rutile with crystallites size in the range of 10-21 nm. The presence of chloride anions and of an acid pH favour the formation of the rutile polymorph as already reported in letterature [10]. Rutile was the only phase isolated when nitrate ions were present confirming that such crystalline structure is formed when the acid concentration is high. The specific surface areas of the powders ranged between 60 and 80 m -g and they were not much influenced by the presence of NaCl, HCl or HNO3. 

To our knowledge this compound has been the subject of only one paper, Chander et al. (1978). The crystalline structure is given as primitive cubic with a = 3.145 A. This result seems unusual in comparison with other rare earth chalcogenides which always exhibit a fee NaCl-type, structure. (By multiplying the parameter by 2, it becomes 6.29 A, which is comparable to that of SmTe and TmTe.)... 

But suppose we mix solid NaCl and solid AgNOa and look for a chemical change. If any reaction occurs, it is slow and virtually undetectable. In fact, the crystalline structures of NaCl and AgNOa are so different that we could separate them by tediously picking out each kind of crystal from the mixture. But if we dissolve the NaCl and AgNOa separately in water and mix the two solutions, we observe the immediate formation of a white, curdlike precipitate of silver chloride. 

The major crystalline structure is ccp with a fee B1 symmetry (NaCl)... 

In chapter 114, O. Vogt and K. Mattenberger examine the magnetic behaviors of the lanthanide and actinide Bl, NaCl-type structures. The magnetic properties of a sample depend upon the spectroscopic state of the f-element and the possibility of J-mixing, the electric crystalline field, the exchange interactions and hybridization. The competition between these various factors can make the materials complicated or simple with respect to their magnetic behaviors. 

The reader should be cautioned that the radius rules above are by no means absolute and in fact are only obeyed 50% of the time. More ionic compoimds have the rock salt (NaCl) structure and fewer have the CsCl structure than would be predicted from the cation/anion radius. StiU, the use of the radius ratio is a good place to start in trying to imderstand the crystalline structure of binary ionically bonded compoimds. 

Crystalline structures of ternary sulphides of rare earth elements may be conventionally classified in two groups. The first group contains ternary sulphides, isostructural binary sulphides of the structure types NaCl, ThjP, a-Gd,S,... 

The structure in Figure 2.14 shows the result of an ionic reaction sodium metal has reacted with chlorine gas to yield white crystalline sodium chloride, NaCl. Each Na atom has lost an electron to form an Na+ cation and each chlorine atom has gained an electron and is hence a CP anion. In practice, the new electron possessed by the chloride came from the sodium atom. 

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