Crystals cubic closest packed

In crystalline C60 the molecules have a face-centered cubic arrangement, i.e. they are packed as in a cubic closest-packing of spheres as they are nearly spherical, the molecules spin in the crystal. The crystals are as soft as graphite. Similar to the intercalation com-... 

Two metals that are chemically related and that have atoms of nearly the same size form disordered alloys with each other. Silver and gold, both crystallizing with cubic closest-packing, have atoms of nearly equal size (radii 144.4 and 144.2 pm). They form solid solutions (mixed crystals) of arbitrary composition in which the silver and the gold atoms randomly occupy the positions of the sphere packing. Related metals, especially from the same group of the periodic table, generally form solid solutions which have any composition if their atomic radii do not differ by more than approximately 15% for example Mo +W, K + Rb, K + Cs, but not Na + Cs. If the elements are less similar, there may be a limited miscibility as in the case of, for example, Zn in Cu (amount-of-substance fraction of Zn maximally 38.4%) and Cu in Zn (maximally 2.3% Cu) copper and zinc additionally form intermetallic compounds (cf. Section 15.4). 

Figure 7.1 Three common crystal lattices adopted by elements (a) body-centred cubic packing, (b) cubic closest packed (or face-centred cubic) and (c) hexagonal closest packed...

Cuthbert and Linnett80 have suggested that the stability of the cubic closest packed arrangement of atoms in crystals of neon, argon, krypton, and xenon (helium crystallizing instead in hexagonal closest packing)81 is explicable by the tetrahedral electron distribution of the atoms... 

Crystal systems, 75 Cubic closest packed (ccp) system. 120... 

The cubic closest-packed arrangement (Figure 10.21b) has three alternating layers, a-b-c-a-b-c. The a-b layers are identical to those in the hexagonal closest-packed arrangement, but the third layer is offset from both a and b layers. Silver, copper, and 16 other metals crystallize with this arrangement. 

Silver metal crystallizes in a cubic closest-packed arrangement with the edge of the unit cell having a length d = 407 pm. What is the radius (in picometers) of a silver atom ... 

In the crystal structure of a-R12 boron, the B12 icosahedra are arranged in approximately cubic closest packing and are linked together in a three-dimensional framework. Figure 9.6.21 shows a layer of interlinked icosahedra perpendicular to the 3-axis, and a perspective view of the crystal structure approximately along the a axis (note the linkage between layers of icosahedra at z = 0,1 /3,2/3,1). Further details are given in Section 13.2. 

Fullerene-C6o is a brown-black crystal, in which the nearly spherical molecules rotate continuously at room temperature. The structure of the crystal can be considered as a stacking of spheres of diameter 1000 pm in cubic closest packing (a = 1420 pm) or hexagonal closest packing (a = 1002 pm, c = 1639pm). Figure 14.1.4 shows the crystal structure of fullerene-C6o. 

The 17 rare-earth metals are known to adopt five crystalline forms. At room temperature, nine exist in the hexagonal closest packed structure, four in the double c-axis hep (dhep) structure, two in the cubic closest packed structure and one in each of the body-centered cubic packed and rhombic (Sm-type) structures, as listed in Table 18.1.1. This distribution changes with temperature and pressure as many of the elements go through a number of structural phase transitions. All of the crystal structures, with the exception of bep, are closest packed, which can be defined by the stacking sequence of the layers of close-packed atoms, and are labeled in Fig. 18.1.1. 

Silver crystallizes in a cubic closest packed structure. The radius of a silver atom is 1.44 A (144 pm). Calculate the density of solid silver. 

Density is mass per unit volume. Thus we need to know how many silver atoms occupy a given volume in the crystal. The structure is cubic closest packed, which means the unit cell is face-centered cubic, as shown in the figure at left. 

Examples of metals that are cubic closest packed are aluminum, iron, copper, cobalt, and nickel. Magnesium and zinc exhibit hexagonal closest packing. Calcium and certain other metals can crystallize in either structure. 

A mineral crystallizes in a cubic closest packed array of sulfur ions with aluminum ions in one-half of the octa-... 

It has been found by experiment that every crystal consists of atoms arranged in a three-dimensional pattern which repeats itself regularly. In a crystal of copper all of the atoms are alike, and they are arranged in a way called cubic closest packing, shown in Figures 3-3 and 3-4. This is a way in which spheres of uniform size may be packed together to occupy the smallest volume. 

Pure, sublimed buckminsterfullerene condenses in a regular face-centered cubic (= cubic closest packed) structure. Complications may occur through the presence of other fullcrcnc impurities or crystallization from a variety of solvents. Sec Hawkins, J. M. Lewis, T. A. Loren, S. D. Meyer, A. Heath, J. R. Saykally, R. J. Hollander, F. J. J. Chem. Soc., Chem. Commun. 1991,175-716, Guo. Y. Kurasawa, N. Goddard, W. A., HI Nature 1991, S5l, 464-467. 

The simplest examples of the closest packing of identical units are the structures of crystalline metals or noble gases and of crystals built of molecules of one kind only. In the latter the molecules must either be approximately spherical in shape or become effectively spherical by rotation or random orientation. Metals provide many examples of hexagonal and cubic closest packing and a few examples of more complex sequences (for example, he. La, Pr, Nd, Am, and chh Sm). Close-packed molecular crystals include the noble gases, hydrogen, HCl, H2S, and CH4. 

In this structure (Fig. 6.1(a)) the A and X atoms alternate in a simple cubic sphere packing, each atom being surrounded by 6 others at the vertices of a regular octahedron. An alternative description, that the A (X) atoms occupy octahedral holes in a cubic closest packing of X (A) atoms is realistic only for compounds such as LiCl in which each Cl is actually in contact with 12 Cl atoms. This structure was derived by Barlow (1898) as a possible structure for crystals composed of... 

The structures of certain crystals are derived from close-packed assemblies from which a proportion of the atoms have been removed in a regular way, as in the ReOs structure in which 0 atoms occupy three-quarters of the positions of cubic closest packing. It is of interest to note here some ways of removing one-half of the atoms from different kinds of closest packings. From a close-packed layer A we remove one-quarter of the atoms as shown in Fig. 29.16(a), and from the layer B above we remove three-quarters of the atoms. This leaves a set of isolated... 

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