Chlorides structures

Chemical Name 2-[(aminocarbonyl)oxv]-N,N,N-trimethvl-1-propanamium chloride Common Name Carbamylmethylcholine chloride Structural Formula ... 

Taking the ionic radii for Cs+, Cl , Br , and I from Table 42, calculate in cubic centimeters per mole the volumes which the cesium halides would have if they crystallized in the sodium chloride structure, nnd compare with the values plotted in Fig. 57. 

Sodium chloride structure. In these two ways of showing the structure, the small spheres represent Na+ ions and the large spheres Cl ions. Note that in any sample of sodium chloride there are equal numbers of Na+ and Cl- ions, but no NaCI molecules. 

Thus, a polyester with the ring in the backbone can be prepared by the Friedel-Crafts polyalkylation of vinyl 2-furoate. BF3 Et20 gave similar results at room temperature in methylene chloride. Structure 30 was arrived at by spectroscopy and by alcoholysis of the polymers. 

Nitrosomonas europaea, 6, 727 Ammonium chloride structure, 1, 5 Ammonium ions... 

FIGURE 5.41 The cesium chloride structure (a) the unit cell and (b) the location of the centers of the ions. 

Estimate the density of each of the following solids from the atomic radii of the ions given in Fig. 1.48 (a) calcium oxide (rock-salt structure, Fig. 5.39) (b) cesium bromide (cesium chloride structure, Fig. 5.41). 

In deriving theoretical values for inter-ionic distances in ionic crystals the sum of the univalent crystal radii for the two ions should be taken, and corrected by means of Equation 13, with z given a value dependent on the ratio of the Coulomb energy of the crystal to that of a univalent sodium chloride type crystal. Thus, for fluorite the sum of the univalent crystal radii of calcium ion and fluoride ion would be used, corrected by Equation 13 with z placed equal to y/2, for the Coulomb energy of the fluorite crystal (per ion) is just twice that of the univalent sodium chloride structure. This procedure leads to the result 1.34 A. (the experimental distance is 1.36 A.). However, usually it is permissible to use the sodium chloride crystal radius for each ion, that is, to put z = 2 for the calcium... 

The Alkali Halides.—In Table V are given the experimental interatomic distances for the alkali halides with the sodium chloride structure, together with the sum of the radii of Table II. 

Alkali Halides with the Sodium Chloride Structure... 

The experimental values for the lithium halides are high. This is due to two different phenomena. In the case of the chloride, bromide and iodide the anions are in mutual contact, that is, the repulsive forces operative are those between the anions, and the anion radius alone determines the inter-atomic distances. The geometry of the sodium chloride structure requires that, for less than 0.414, the anions come into contact... 

Huggins, who has particularly emphasized the fact that different atomic radii are required for different crystals, has recently [Phys. Rev., 28, 1086 (1926)] suggested a set of atomic radii based upon his ideas of the location of electrons in crystals. These radii are essentially for use with crystals in which the atoms are bonded by the sharing of electron pairs, such as diamond, sphalerite, etc. but he also attempts to include the undoubtedly ionic fluorite and cesium chloride structures in this category. 

The alkali halides with the cesium chloride structure also show satisfactory agreement, the observed values being about 2.5% larger than the sum of the theoretical radii. 

Other Binary Compounds.—Scandium nitride and zirconium and titanium carbide do not conform with the theoretical radii. It is possible that these crystals do not consist essentially of Sc+3, N 3, Ti+4, Zr+4 and C-4 ions, especially since zirconium and titanium nitride, ZrN and TiN, also form crystals with the sodium chloride structure but possibly also the discrepancy can be attributed to deformation of the anions, which have very high mole refraction values. 

The Sodium Chloride and Cesium Chloride Structures.—The agreement found between the observed inter-atomic distances and our calculated ionic radii makes it probable that the crystals considered are built of only slightly deformed ions it should, then, be possible, with the aid of this conception, to explain the stability of one structure, that of sodium chloride, in the case of most compounds, and of the other, that of cesium chloride, in a few cases, namely, the cesium and thallous halides. 

These considerations also explain the occurrence of cases of dimorphism involving the sodium chloride and cesium chloride structures. It would be expected that increase in thermal agitation of the ions would smooth out the repulsive forces, that is, would decrease the value of the exponent n. Hence the cesium chloride structure would be expected to be stable in the low temperature region, and the sodium chloride structure in the high-temperature region. This result may be tested by comparison with the data for the ammonium halides, if we assume the ammonium ion to approximate closely to spherical symmetry. The low-temperature form of all three salts, ammonium chloride, bromide and iodide, has the cesium chloride structure, and the high-temperature form the sodium chloride structure. Cesium chloride and bromide are also dimorphous, changing into another form (presumably with the sociium chloride structure) at temperatures of about 500°. 

The Transition to the Sphalerite Structure.—The oxide, sulfide and selenide of beryllium have neither the sodium chloride nor the cesium chloride structure, but instead the sphalerite or the wurzite structure. The Coulomb energy for the sphalerite arrangement is... 

In Table XVIII are given values of the radius ratio for the salts of beryllium, magnesium and calcium (those of barium and strontium, with the sodium chloride structure, also obviously satisfy the radius ratio criterion). It is seen that all of the sodium chloride type crystals containing eight-shell cations have radius ratios greater than the limit 0.33, and the beryl-... 

The effect of double repulsion for the sodium chloride structure may raise this limit a few per cent. 

Sodium chloride structure Sphalerite or wurzite structure... 

The prediction may be made that the still unstudied crystal magnesium telluride, with the radius ratio 0.29, has the sphalerite or wurzite structure rather than the sodium chloride structure. 

The radius ratios for sphalerite and wurzite type crystals with eighteen-shell cations do not conform to our criterion, so that some other influence must be operative. Without doubt this is deformation. Here again it is seen that the tetrahedral structure is particularly favorable to deformation, for the observed Zn++—O distance (1.93 A.) is 0.21 A. shorter than the theoretical one, while in cadmium oxide, with the sodium chloride structure, the difference is only 0.01 A. 

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