Crystalline solids atomic

In atomic crystalline solids, atoms are covalently bonded to each other. In covalent bonding, electrons are shared equally by the bonding atoms. 

The alkali metals barium (Ba) and uranium (U) are atomic crystalline solids. Their atoms pack in a body-centered cubic arrangement. 

Use nine 2-in.-diameter balls and eight toothpicks to form three layers of a body-centered cubic crystal, as illustrated in Figure 4.6 (the top layer is the same as the bottom layer). Put the layers together like a sandwich. Draw a picture of this atomic crystalline solid. 

From this activity, it would appear that metals form atomic crystalline solids. However, different metals have adopted different atomic packing arrangements. Offer an explanation for this occurrence. 

The three-dimensional synnnetry that is present in the bulk of a crystalline solid is abruptly lost at the surface. In order to minimize the surface energy, the themiodynamically stable surface atomic structures of many materials differ considerably from the structure of the bulk. These materials are still crystalline at the surface, in that one can define a two-dimensional surface unit cell parallel to the surface, but the atomic positions in the unit cell differ from those of the bulk structure. Such a change in the local structure at the surface is called a reconstruction. 

Here is the distance between the molecule i in the gas phase (or, for a complex molecule, the centre of its atom i) and the centre of an atom j in the solid. If a particular face of a crystalline solid is being considered, the various values of r, can be expressed in terms of a single quantity z here z is the distance between the centre of the gas molecule (or a given atom or group thereof) and the plane through the centres of the atoms in the outermost layer of the solid. 

A crystalline solid is never perfect in that all of tire lattice sites are occupied in a regular manner, except, possibly, at the absolute zero of temperature in a perfect crystal. Point defects occur at temperatures above zero, of which the principal two forms are a vacant lattice site, and an interstitial atom which... 

In our discussion so far we have begged the question of just how the atoms in a solid move around when they diffuse. There are several ways in which this can happen. For simplicity, we shall talk only about crystalline solids, although diffusion occurs in amorphous solids as well, and in similar ways. 

To melt ice we have to put heat into the system. This increases the system entropy via eqn. (5.20). Physically, entropy represents disorder and eqn. (5.20) tells us that water is more disordered than ice. We would expect this anyway because the atoms in a liquid are arranged much more chaotically than they are in a crystalline solid. When water freezes, of course, heat leaves the system and the entropy decreases. 

EXAFS is a nondestructive, element-specific spectroscopic technique with application to all elements from lithium to uranium. It is employed as a direct probe of the atomic environment of an X-ray absorbing element and provides chemical bonding information. Although EXAFS is primarily used to determine the local structure of bulk solids (e.g., crystalline and amorphous materials), solid surfaces, and interfaces, its use is not limited to the solid state. As a structural tool, EXAFS complements the familiar X-ray diffraction technique, which is applicable only to crystalline solids. EXAFS provides an atomic-scale perspective about the X-ray absorbing element in terms of the numbers, types, and interatomic distances of neighboring atoms. 

Crystalline solids at temperatures above absolute zero are never perfeet in that all lattiee sites are oeeupied in a eompletely regular manner. Imperfeetions exist. Formation of sueh sites is endothermie a small quantity of energy is required. Point defeets oeeur, of whieh the prineipal two are a vacant lattiee site, and an interstitial atom that oeeupies a volume between a group of atoms on normal sites that affeets erystal purity (see Hull and Baeon, 2001, for a detailed exposition). 

For a substance to dissolve in a liquid, it must be capable of disrupting the solvent structure and permit the bonding of solvent molecules to the solute or its component ions. The forces binding the ions, atoms or molecules in the lattice oppose the tendency of a crystalline solid to enter solution. The solubility of a solid is thus determined by the resultant of these opposing effects. The solubility of a solute in a given solvent is defined as the concentration of that solute in its saturated solution. A saturated solution is one that is in equilibrium with excess solute present. The solution is still referred to as saturated, even... 

The halogens are volatile, diatomic elements whose colour increases steadily with increase in atomic number. Fluorine is a pale yellow gas which condenses to a canary yellow liquid, bp — 188.UC (intermediate between N2, bp —195.8°, and O2, bp — 183.0°C). Chlorine is a greenish-yellow gas, bp —34.0°, and bromine a dark-red mobile liquid, bp 59.5° interestingly the colour of both elements diminishes with decrease in temperature and at —195° CI2 is almost colourless and Br2 pale yellow. Iodine is a lustrous, black, crystalline solid, mp 113.6°, which sublimes readily and boils at 185.2°C. 

Brittle fracture may be considered, therefore, as two layers of atoms being pulled apart until the interatomic forces fall below their maximum (Fig. 8.82). Using this information it is possible to calculate the fracture strength of a perfect crystalline solid (a,h), e.g. 

FIGURE 5-16 Crystalline solids have well-defined faces and an orderly internal structure. Each face of the crystal is formed by the top plane of an orderly stack of atoms, molecules, or ions. 

A crystalline solid is a solid in which the atoms, ions, or molecules lie in an orderly array (Fig. 5.16). A crystalline solid has long-range order. An amorphous solid is one in which the atoms, ions, or molecules lie in a random jumble, as in butter, rubber, and glass (Fig. 5.17). An amorphous solid has a structure like that of a frozen instant in the life of a liquid, with only short-range order. Crystalline solids typically have flat, well-defined planar surfaces called crystal faces, which lie at definite angles to one another. These faces are formed by orderly layers of atoms (Box 5.1). Amorphous solids do not have well-defined faces unless they have been molded or cut. 

We classify crystalline solids according to the bonds that hold their atoms, ions, or molecules in place ... 

Crystalline solids have a regular internal arrangement of atoms or ions amorphous... 

Six members of this series could be isolated in modest yields as highly air-sensitive, dark blue or dark purple crystalline solids for which analytical, spectroscopic, and single-crystal X-ray analyses were fully consistent with the side-on-biidged N2 structures shown in Scheme 102. These complexes show unusual structural features as well as a unique reactivity. An extreme degree of N = N bond elongation was manifested in rf(N-N) values of up to 1.64 A, and low barriers for N-atom functionalization allowed functionalization such as hydrogenation, hydrosilylation, and, for the first time, alkylation with alkyl bromides at ambient temperature. ... 

A pure crystalline solid comes closest to the depiction in Figure 14-1 la. Nevertheless, each atom or molecule in a pure crystalline solid vibrates back and forth in its compartment, and this vibration can be thought of as similar to the depiction in 14-1 Ic. The vibrations move the atoms or molecules randomly about over the space available to them, making IV > 1 and S > 0. 

The underlying principle of X-ray diffraction is as follows. When a beam of X-rays passes through a crystalline solid it meet various sets of parallel planes of atoms. The diffracted beams cancel out unless they happen to be in phase, the condition for which is described in the Bragg relationship ... 

Crystalline solids are built up of regular arrangements of atoms in three dimensions these arrangements can be represented by a repeat unit or motif called a unit cell. A unit cell is defined as the smallest repeating unit that shows the fuU symmetry of the crystal structure. A perfect crystal may be defined as one in which all the atoms are at rest on their correct lattice positions in the crystal structure. Such a perfect crystal can be obtained, hypothetically, only at absolute zero. At all real temperatures, crystalline solids generally depart from perfect order and contain several types of defects, which are responsible for many important solid-state phenomena, such as diffusion, electrical conduction, electrochemical reactions, and so on. Various schemes have been proposed for the classification of defects. Here the size and shape of the defect are used as a basis for classification. 

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