Crystalline solids hexagonal structure

Greenish blue to black crystalline solid hexagonal or cubic crystals dia-mond-like structure density 3.217g/cm3 exceedingly hard, Mohs hardness 9.5 sublimes at about 2,700°C dielectric constant 7.0 electron mobility >100 cm /volt-sec hole mobility >20cm2/volt-sec band gap energy 2.8 eV insoluble in water and acids solubilized by fusion with caustic potash. 

Grayish-white, lustrous, brittle, crystalline solid, hexagonal, rhombohedral structure, or dark-gray to brown, amorphous powder with metal characteristics, d (cryst) 6.tl-6.27. mp 449.8". bp 989.9". Electrical resistivity (19.6") 200,000, -ohms-cm. Latent heat of fusion 4,27 keal/mote. Linear coefficient of thermal expansion 16.8 x 10- /°C. 

The particles formed are in most cases spherical, although rods, ellipsoids, platelets, and hexagonal structures have also been produced. Solids composed of spherical particles are as a rule amorphous, while those of other morphologies are crystalline. In general, aging times of 2 h at approximately 100°C were sufficient to produce the desired results however, in some instances much longer times were necessary to complete the precipitation process. 

Ice (H20) is a molecular crystalline solid. Six water molecules bond to each other to form a hexagonal pattern. This pattern is reflected in the hexagonal geometry exhibited in snowflakes. In Activity 4.1, you will construct models of basic crystalline solids and grow molecular-solid crystals. Then you will consider the basic structures of crystalline solids and look upon these structures as three-dimensional works of art. 

In Activity 4.1, students described and modeled crystalline solids according to the way their atoms packed into a regular structure. We found that their atoms could pack into face-centered, body-centered, or hexagonal-closest arrangements. Another way to understand the structure of a crystalline solid is to consider the bonding forces between its structural units. 

When we determined the crystalline structure of solids in Chapter 4, we noted that most transitional metals form crystals with atoms in a close-packed hexagonal structure, face-centered cubic structure, or body-centered cubic arrangement. In the body-centered cubic structure, the spheres take up almost as much space as in the close-packed hexagonal structure. Many of the metals used to make alloys used for jewelry, such as nickel, copper, zinc, silver, gold, platinum, and lead, have face-centered cubic crystalline structures. Perhaps their similar crystalline structures promote an ease in forming alloys. In sterling silver, an atom of copper can fit nicely beside an atom of silver in the crystalline structure. 

Crystalline solids consist of periodically repeating arrays of atoms, ions or molecules. Many catalytic metals adopt cubic close-packed (also called face-centred cubic) (Co, Ni, Cu, Pd, Ag, Pt) or hexagonal close-packed (Ti, Co, Zn) structures. Others (e.g. Fe, W) adopt the slightly less efficiently packed body-centred cubic structure. The different crystal faces which are possible are conveniently described in terms of their Miller indices. It is customary to describe the geometry of a crystal in terms of its unit cell. This is a parallelepiped of characteristic shape which generates the crystal lattice when many of them are packed together. 

Another interesting feature of the solid state structure is the long range packing of the Ln(btsa)3 molecules (Fig. 9). The presence of large hexagonal spaces within the crystal lattice might induce a facile phase transition, e.g., reorientation of the molecules in the crystalline lattice [115] and inclusion of solvent molecules [99b, 108], and therefore be responsible for the lack of quality of the solid state structure determinations. 

Five phases of titanium boride have been reported. TiB2 [12405-65-35], TL,B [12505-68-9], TiB [12007-08-8], TL,B5 [12447-59-5], and TiB12 [51311-04-7]. The most important of these is the diboride, TiB2, which has a hexagonal structure and lattice parameters of a = 302.8 pm and c = 322.8 pm. Titanium diboride is a gray crystalline solid. It is not attacked by cold concentrated hydrochloric or sulfuric acids, but dissolves slowly at boiling temperatures. It dissolves more readily in nitric acid/hydrogen peroxide or nitric acid/sulfuric acid mixtures. It also decomposes upon fusion with alkali hydroxides, carbonates, or bisulfates. 

TiCl3 generated from the reduction of TiCl4 and AlEt3 exists in four crystalline forms a, /3, y, and 8. The [3 form has a chain structure and is brown in color, while the other three have layer structures and are purple in color. The solid-state structures of a and y may be described as hexagonal and cubic close-packed arrays of chloride ions, respectively. Two-thirds of the octahedral holes of the close-packed arrays are filled by Ti3+ ions. The 8 form is more disordered than both a and y. 

Earth s inner core (blue region) consists of iron that is under such great pressure that it is believed to be a crystalline solid, despite temperatures above 4000°C. The crystal may have a hexagonal close-packed structure or its own unique structure. The red region shows the molten iron core that is responsible for Earth s magnetic field. 

Strontium carbonate is a colorless or white crystalline solid having a rhombic structure below 926°C and a hexagonal structure above this temperature. It has a specific gravity of 3.70, a melting point of 1497°C at 6 MPa (60 atm), and it decomposes to the oxide on heating at 1340°C. It is insoluble in water but reacts with acids, and is soluble in solutions of ammonium salts. 

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