NaCl lattice

CdO is produced from the elements and, depending on its thermal history, may be greenish-yellow, brown, red or nearly black. This is partly due to particle size but more importantly, as with ZnO, is a result of lattice defects — this time in an NaCl lattice. It is more basic than ZnO, dissolving readily in acids but hardly at all in alkalis. White Cd(OH)2 is precipitated from... 

Determination of Lattice Breakup Energies from Experimental Data The process of lattice breakup can be split into individual steps for which the energies can be measured. Thus, breaking up the NaCl lattice to form free ions in the gas phase can be described (with a Born-Haber cycle) as... 

Kagan and Maslov (20) have calculated f for the diatomic NaCl lattice. Their results are given in terms of the Cn and C44 elastic constants and the atomic masses and they agree moderately well (6, 13) with the data. 

Figure 2 depicts different forms of chemisorption for a Na atom and a Cl atom on the NaCl lattice (5). Figure 2a corresponds to weak binding of a Na atom to the lattice. We investigated this type of bond in 1947 (6-5). The bond is effected by the valence electron of the Na atom, which is to a greater or lesser degree drawn into the lattice. In other words, the electron cloud surrounding the positive framework of the Na atom, which in case of the isolated atom was spherically symmetrical, is now deformed and... 

The phase Fe0.93O can be described as a solid solution of 0 79 mol FeO and 0 07 mol Fe203. At higher temperature, phases with other compositions become stable, but the composition never reaches that of the pure compound FeO. The pure compound FeO does not exist it only occurs when stabilized by some admixture of Fe203. In the stabilized form, the Fe2 and Fe3 ions and the gaps are distributed at random over the cation positons in the NaCl lattice. 

It will depend on the special form of the lattice and the possible valencies what kind of solid solution, with cation and anion gaps, is formed. In some cases, both processes can take place simultaneously it has been found that the compound CbO has a NaCl lattice, with 25 per cent gaps in both the Cb2 and O2" positions. 

CsCl lattice, which we can call a8 if aQ is the distance in the NaCl lattice, is equal to ae(8xiej6A8)l/in 1 where A8 and A8 are respective Madelung constants for the NaCl and CsCl lattices. 

As long as we only assume coulomb forces and repulsive forces of the type discussed, this contraction leads to the surprising result that the CsCl lattice can never be formed. It can only exist if the lattice energy of the CsCl lattice is smaller, or at least equal to that of the NaCl lattice. The conditions for the stability of the CsCl lattice are... 

Potassium, rubidium and cesium orthoplumbates M4Pb04 (M = K, Rb, Cs) all contain isolated [Pb04] tetrahedra, as does Rb3NaPbO4.348-3S0 The structure of the metaplumbate , Li2Pb03, like Li2Sn03, is a variant of the NaCl lattice, with octahedrally coordinated lead,351... 

The NaCl lattice has the cubic unit cell shown in Fig. 10-7. KBr also crystallizes this lattice. 

Lithium iodide crystallizes in the NaCl lattice in spite of the fact that r+/r is less than 0.414. Its density is 3.49 g/cm3. Calculate from these data the ionic radius of the iodide ion. 

An x-ray powder investigation 109) of KSiH3, RbSiH3 and CsSiH3 confirmed that all salts are isomorphous, crystallizing fee in the NaCl lattice. The lattice parameters are as follows... 

The contribution of the London energy to the lattice energy of the alkali halides is indeed small in comparison with the electrostatic interaction but the transition from NaCl- to CsCl type of lattice nevertheless depends on it. The geometrical condition, r+/r > 0.71, is not sufficient in fact KF with r+/r = 1.00 has the NaCl lattice (p. 32). 

At higher pressures also the corresponding rubidium halides attain the CsCl lattice which corresponds to a lower molar volume. At 4450 CsCl goes over into a modification with the NaCl lattice. 

The crystal structure of the ammonium halides, which, with the exception of NH4F, have modifications with the CsCl-and the NaCl lattice, cannot be understood along these lines the structure of the NH4+ ion plays an important part. 

Binary compounds are few, those of importance being the halides (Section 17-B-2) and the black oxide (VO), which has an NaCl lattice but is prone to nonstoichiometry (obtainable with 45-55 at. % oxygen). It has somewhat metallic physical characteristics. Chemically it is basic, dissolving in mineral acids to give V" solutions. 

NaCl (solid) The coordination number of each atom in the NaCl lattice is six. Therefore, further weakening of the Na-Cl bond is observed (c.f. Sec. 4.2.2.4). An instructive example illustrating the difference between terminal and bridging bonds is found among the boranes ... 

A further problem in the interpretation of vibrational spectra of solid state compounds arises from the different phases of the vibrations in neighboring cells, leading to a wave described by the wave vector k. In the absence of a phase difference, k equals zero. This is the basis for the factor group analysis. If the vibrational motions are oriented parallel to the direction of the wave caused by the phase differences, a longitudinal branch results while transverse branches result from orthogonal vibrational motions. Furthermore, it is necessary to differentiate between optical and acoustic modes. In the optical mode of the NaCl lattice, Na+ and Cl ions have opposite displacements, while the acoustic modes are caused by in-phase motions of Na+ and CF. 

Tin(II) oxide exists in several modifications. The commonest is blue-black tetragonal tin(II) oxide, formed by alkaline hydrolysis of a tin(II) salt it has a layer lattice with square pyramidal coordination at tin and equal Sn-O distances (Sn- Sn distances between Sn atoms in adjacent layers are 3.70 A, close to the values in pSn). Tin(II) oxide is amphoteric and dissolves in aqueous acid and aUcahes. Tin(II) hydroxide, Sn(OH)2, has been obtained from MesSnOH and SnCl2. Tin(II) sulfide has a structure with parallel zigzag Sn S chains, which are connected by short interchain Sn- S contacts this gives a basic pyramidal [SnSs] unit. Tin(II) selenide (mp 861 °C) exhibits one phase which is isomorphous with SnS and a second cubic phase with the NaCl lattice the latter is also taken up by tin(II) telluride. 

In what follows only NaCl lattices with monovalent ions are considered. It is assumed that the ions are at rest (i.e. have no thermal motions) and also that the elastic forces are independent of the polarization of the ions (the electron shift). 

The elastic forces decrease proportionally to a high power of the distance, so that we need only consider the nearest ions. In the NaCl lattice there are six of these, forming a regular octahedron about the central ion. For the sake of simplicity we shall only consider displacements in the principal direction (fig. i). If v and v are equal to unity, the elastic force between two ions is... 

Ammonium chloride, NH4CI, crystallizes in a CsCl lattice up to a temperature of 174-3 0 and above that temperature, in the NaCl lattice. Similar behaviour is observed with ammonium bromide (temperature of transformation 137-8 C) and ammonium iodide (temperature of transformation — /I7-6 C). The interionic distances in the CsGl lattice are actually found to be approximately 3 per cent greater than in the NaGl... 

The significance of these critical ratios was first pointed out by Magnus for ionic complexes and later applied by Goldschmidt to crystals. In the case of GsCl, CsBr and Csl, the value of the ratio rA is greater than 0 73. It is therefore understandable that these salts form crystals with a coordination number of eight. There are, however, many exceptions to the conditions formulated above. For example, the halides of rubidium, potassium chloride and potassium fluoride, which crystallize with a NaCl lattice, have a value of rA greater than 0 732. 

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