Sodium chloride lattice structure

The structure-dependent coefficients have been calculated for the three primitive cubic lattices.4 For the sodium chloride lattice we have A — 2a3, where a denotes the anion-cation lattice spacing, and if we define a parameter bi by the equation... 

Spectra of the compounds with sodium chloride crystal structure (Fig. 24) show strong resemblance. Quantitative correlation between lattice parameters and absorption maxima is poor as seen on Table II. 

The sodium chloride structure. Sodium chloride crystallizes in a face-centered cubic structure (Fig. 4.1a). To visualize the face-centered arrangement, consider only the sodium ions or the chloride ions (this will require extensions of the sketch of the lattice). Eight sodium ions form the comers of a cube and six more are centered on the faces of the cube. The chloride ions are similarly arranged, so that the sodium chloride lattice consists of two interpenetrating face-centered cubic lattices. The coordination number (C.N.) of both ions in the sodium chloride lattice is 6. that is, there are six chloride ions about each sodium ion and six sodium ions about each chloride ion. 

Sulfide compounds are formed by all of the Group IVA elements, and lead is found as the sulfide in its principle ore galena that has Pb2+ and S2 ions in a sodium chloride lattice (see Chapter 3). A chain structure is shown by SiS2 in which each Si is surrounded by four S atoms in an approximately tetrahedral environment ... 

The structure of MnO consists of discrete Mn2+ and O2- ions in a sodium chloride lattice. 

AgF, AgCl and AgBr crystallize with a sodium chloride lattice and CuCl, CuBr, and Cul with the lattice given in Figure 62 in which copper has a coordination number of four. This difference in crystal structure of the two salts is not determined by the difference in the dimensions of the Ag"+ and Cu+ ions, since according to Pauling the latter has the value 0-96 A, which is not outside the limits for a sodium chloride lattice. The decrease of the coordination number from six to four and the formation of a tetrahedral configuration are more probably determined by the covalent character of the bonds between copper and chlorine. However, it is to be emphasized that the bonds are not entirely covalent any more than they are entirely ionic, but are of an intermediate... 

Mercuric sulfide, HgS, is precipitated from aqueous solutions as a black, highly insoluble compound. The solubility product is 10 54, but the sulfide is somewhat more soluble than this figure would imply because of some hydrolysis of Hg2+ and S2- ions. The black sulfide is unstable with respect to a red form identical with the mineral cinnabar and changes into it when heated or digested with alkali polysulfides or mercurous chloride. The red form has a distorted sodium chloride lattice with Hg—S chains similar to those in HgO. Another form, occurring as the mineral metacinnabarite, has a zinc blende structure, as have the selenide and telluride. 

The phenomenon of superconductivity is common in several particular types of compounds. Thus more than two dozen binary compounds with the fee sodium chloride (NaCl) structure are superconducting. The carbides AC and nitrides AN, such as NbN with Eg = 17 K, have the highest transition temperatures of this group, and the metallic A atoms with Eg values above 10 K were Nb, Mo, Ta, W, and Zr. The NaCl-type superconductors are compositionally stoichiometric but not structurally so. In other words, these compounds have a small to moderate concentration of vacancies in the lattice. For example, YS has 10% vacancies, which means that its chemical formula should properly be written Yo.gSo.g. Nonstoichiometric NaCl-type compounds such as Tai gCoje also exist. Ordinarily the vacancies are random, but sometimes they are ordered. 

Crystals of sodium chloride have a lattice structure, a Describe a sodium chloride lattice, b Explain the following properties of sodium chloride. 

Figure 5.18.1 The NaCl crystal structure consisting of two interpenetrating face-centered cubic lattices. The face-centered cubic arrangement of sodium cations (the smaller spheres) is readily apparent with the larger spheres (representing chloride anions) filling what are known as the octahedral holes of the lattice. Calcium oxide also crystallizes in the sodium chloride structure.

The formation energy of Schottky defects in NiO has been estimated at 198 kJ mol-1. The lattice parameter of the sodium chloride structure unit cell is 0.417 nm. (a) Calculate the number of Schottky defects per cubic meter in NiO at 1000°C. (b) How many vacancies are there at this temperature (c) Estimate the density of NiO and hence the number of Schottky defects per gram of NiO. 

In most ionic crystals, the anion is larger than the cation and, therefore, the packing of the anions determines the arrangement of ions in the crystal lattice. There are several possible arrangements for ionic crystals in which the anions are larger than cations, and cations and anions are present in equal molar amounts. For example. Figure 4.22 shows two different arrangements found in the structures of sodium chloride, NaCl, and cesium chloride, CsCl. 

Figure 5-3 The lattice structure of an ionic solid, sodium chloride.

The structures of the hydrides, oxides and nitrides in this group are rather peculiar, for they can always be described as lattices, as found in pure metals, with the negative ions inserted in the octahedral holes of these structures. In the case of TiN, TiO and, in general, all compounds AB, all octahedral holes are occupied, and the structure is that of the sodium chloride type. There are nitrides of other types, too, e.g. A2N, A3N, etc., in which cases only a part of the octahedral holes are occupied. 

Where the lithium ions fit best will be determined by their size relative to the iodide ions. Note from above that there are two types of interstices in a closest packed structure. These represent tetrahedral (f) and octahedral (o) holes because the coordination of a small ion fitted into them is either tetrahedral or octahedral (see Fig. 4.12). The octahedral holes are considerably larger than the tetrahedral holes and can accommodate larger cations without severe distortion of the structure. In lithium iodide the lithium ions fit into the octahedral holes in a cubic closest packed lattice of iodide ions. The resulting structure is the same as found in sodium chloride and is face-centered (note that face-centered cubic and cubic closest packed describe the same lattice). 

Upon evaporation of (lie sulvent, the salt is obtained as such, frequently as crystals, sometimes with and sometimes without water of crystallization. A salt, when dissolved in an ionizing solvent, or fused (e.g., sodium chloride in water), is a good conductor of electricity and when rn the solid state forms a crystal lattice (e.g., sodium chloride crystals possess a definite lattice structure tor both sodium cations (Na+) and chloride anions (Cl-), determinable by examination with x-rays). 

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