Metal body-centered cubic structure

The metal has a bright silvery metallic luster. Neodymium is one of the more reactive rare-earth metals and quickly tarnishes in air, forming an oxide that spalls off and exposes metal to oxidation. The metal, therefore, should be kept under light mineral oil or sealed in a plastic material. Neodymium exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at 863oC. 

As with other related rare-earth metals, gadolinium is silvery white, has a metallic luster, and is malleable and ductile. At room temperature, gadolinium crystallizes in the hexagonal, close-packed alpha form. Upon heating to 1235oG, alpha gadolinium transforms into the beta form, which has a body-centered cubic structure. 

Potassium. K aw 39.102 at no 19 valence 1 soft, silvery metal, rapidly oxidized in moist air body-centered cubic structure mp 63° bp 770° d 0.862g/cc. Sol in liq ammonia, aniline, Hg and Na... 

Although the comer atoms must move apart to convert a simple cube into a body-centered cube, the extra atom in the center of the stracture makes the body-centered cubic lattice more compact than the simple cubic structure. All the alkali metals, as well as iron and the transition metals from Groups 5 and 6, form ciystals with body-centered cubic structures. 

Disordered alloys may form when two metals are mixed if both have body-centered cubic structures and if their atomic radii do not differ by much (e.g. K and Rb). The formation of ordered alloys, however, is usually favored at higher temperatures the tendency towards disordered structures increases. Such an arrangement can even be adopted if metals are combined which do not crystallize with body-centered cubic packings themselves, on condition of the appropriate composition. /J-Brass (CuZn) is an example below 300 °C it has a CsCl structure, but between 300 °C and 500 °C a A type transformation takes place resulting in a disordered alloy with a body-centered cubic structure. 

Figure 5.8 Interstitial diffusion (a) interstitial diffusion involving the direct migration of an interstitial atom to an adjacent site in the crystal (b, c) some of the octahedral and tetrahedral interstitial sites in the body-centered cubic structure of metals such as iron and tungsten and (d) the total number of octahedral and tetrahedral sites in a unit cell of the body-centered cubic structure. Diffusion paths parallel to the unit cell edges can occur by a series of alternating octahedral and tetrahedral site jumps, dashed line.

Here, as in other branches of inorganic chemistry, interatomic distances show a considerable variation and, although some correlation with bond order is possible, attempts to do so should be regarded with caution.For metals with close-packed structures, the coordination number of any atom is 12 for cubic or hexagonal structures, and 14 (8 plus 6 more neighbors at about 15% further away) for body-centered cubic structures. In general, this number exceeds the number of electrons per atom available for metal-metal bond formation and precludes the formation of localized, two-electron bonds between metal atoms. Bond orders of less than 1 are therefore commonly recorded. For metal clusters, it is necessary to consider the variety of ways in which valence electrons may be utilized in chemical bonding within the Mm... 

FIG. 11.8 (a) A section of the difference synthesis through the Cr nucleus, parallel to the (110) plane. Contours are drawn at intervals of 0.2 eA 3. (b) Theoretical contour map of valence electron distribution on the (110) plane for chromium metal. Contours are drawn at intervals of 0.5 eA-3. The lobes point towards the nearest neighbors in the body-centered cubic structure. Source Ohba et al. (1982). 

Golden yellow, soft and ductile metal body-centered cubic structure density 1.93 g/cm melts at 28.44°C vaporizes at 671°C vapor pressure 1 torr at 280°C electrical resistivity 36.6 microhm-cm (at 30°C) reacts with water dissolves in liquid ammonia forming a blue solution. 

Silvery metal body-centered cubic structure imparts crimson-red color to flame density 0.862g/cm3 at 20°C melts at 63.25°C density of hquid potassium at 100°C is 0.819 g/cm and 0.771g/cm3 at 300°C vaporizes at 760°C vapor pressure 123 torr at 587°C electrical resistivity 6.1 microhm-cm at 0°C and 15.31 microhm-cm at 100°C viscosity 0.25 centipoise at 250°C surface tension 86 dynes/cm at 100°C thermal neutron absorption cross section 2.07 barns reacts violently with water and acids reacts with alcohol dissolves in liquid ammonia and mercury... 

Pale yellow metal attains a green oxide coating on exposure to air exhibits two crystalline modifications (1) an alpha form, that has a hexagonal close-packed structure, a density of 6.773 g/cm and a molar volume 20.82 cc/mol, and (2) a beta form that has an open body-centered cubic structure having a density of 6.64 g/cm and a molar volume of 21.20 cc/mol. The alpha form transforms to beta at 792°C. 

Soft, bright, silvery metal malleable, can be readily cut with a knife or extruded as wire liquid sodium in inert atmosphere appears like mercury blue vapor, appears brilliant green at high temperatures imparts golden-yellow color to flame body-centered cubic structure paramagnetic density 0.97... 

A bright white metal soft and ductile body-centered cubic structure index of refraction 3.03 density 5.96 g/cm melts at 1,910°C vaporizes at 3,407°C electrical resistivity, 18.1 microhm-cm at 0°C and 20.1 microhm-cm at 25°C magnetic susceptibility 1.4x10 cgs units modulus of elasticity 18-19x10 psi shear modulus 6.73xl0 psi Poisson s ratio 0.36 thermal neutron absorption cross section 5 barns/atom insoluble in water, dilute sulfuric acid, and hydrochloric acid at all concentrations soluble in nitric acid, aqua regia, and concentrated sulfuric acid insoluble in alkalies. 

Silvery gray lustrous metal or bluish black amorphous powder close-packed hexagonal lattice transforms to a body-centered cubic structure at 865°C density 6.506 g/cm melts at about 1,852°C vaporizes at 4,377°C elec-... 

The density of beryllium is 1.847 g/cm3 based upon average values of lattice parameters at 255C (a — 22.856 nm and c — 35.832 nm). Beryllium products generally have a density around 1.850 g/cm3 or higher because of impurities, such as aluminum and other metals, and beryllium oxide. The crystal structure is close-packed hexagonal. The alpha-form of beryllium transforms to a body-centered cubic structure at a temperature very close to the melung point. 

Many metals have close-packed structures, with the atoms stacked in either a hexagonal or a cubic arrangement close-packed atoms have a coordination number of 12. Some metals have body-centered cubic structures, but primitive cubic structures are rare. 

If you try to draw an electron-dot structure for a metal, you ll quickly realize that there aren t enough valence electrons available to form an electron-pair bond between every pair of adjacent atoms. Sodium, for example, which has just one valence electron per atom (3s1), crystallizes in a body-centered cubic structure in which each Na atom is surrounded by eight nearest neighbors (Section 10.8). Consequently, the valence electrons can t be localized in a bond between any particular pair of atoms. Instead, they are delocalized and belong to the crystal as a whole. 

Potassium metal crystallizes in a body-centered cubic structure. Draw one unit cell, and try to draw an electron-dot structure for bonding of the central K atom to its nearest-neighbor K atoms. What is the problem ... 

Describe the electron-sea model of the bonding in cesium metal. Cesium has a body-centered cubic structure. 

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. 

One of the earliest applications of the method of different orbitals for different spins appears in Slater s classic study of the cohesion of monovalent metals 133>. In Slater s model of the body-centered cubic structure of the alkali metals, the lowest unperturbed, zero spin-state is taken to be one in which the valence electrons about the atoms at the cube-comers have one spin, spin , while those at the cube-centers have the opposite spin, spin (3. 

Both K4C60 and Rb o are tetragonal, and the structure of M6C60 at room temperature is body-centered cubic. These metal fullerides are all insulators. 

A body-centered cubic structure (adopted by some of the metals) has spheres... 

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