Interatomic bonding

The forces which hold atoms together (the interatomic bonds) which act like little springs, linking one atom to the next in the solid state (Fig. 4.1). 

Atoms move by making and breaking interatomic bonds and by minor "shuffling". 

Fig. 17.1. (a) Dislocation motion is intrinsically easy in pure metals - though alloying to give solid solutions or precipitates con moke it more difficult. (b) Dislocation motion in covalent solids is intrinsically difficult because the interatomic bonds must be broken and reformed. ( ) Dislocation motion in ionic crystals is easy on some planes, but hard on others. The hard systems usually dominate. 

The most important interatomic bond in polymers, and indeed in organic chemistry, is the covalent bond. This is formed by the sharing of one or more pairs of electrons between two atoms. An example is the bonding of carbon and hydrogen to form methane Figure 5.2). 

DOPED PA MODELS. We selected two criteria to characterize the structure of the mono- and di-cations. The wavefunctions of the cations at their respective optimized geometries were used to determine Mayer s bond indices which reflect the strength of the interatomic bonds. The differences in the cations and also the neutral molecule emerge very clearly from Table III. 

In semiconductors such as silicon, each atom in the structural lattice has four outer electrons, each of which covalently pairs with an electron from one of the four neighboring atoms to form the interatomic bonds, i.e.- the "diamond" structure. Completely pure silicon thus has essentially no electrons available at room temperature for electron conduction, making it a very poor conductor. However, the key is getting the silicon pure enough. Originally, silicon was thought to be a natural semi-conductor until really pure silicon became available. 

Fig. 2 Differences between wurtzite (WZ) and zincblende (ZB) forms, (a, b) Handedness of the fourth interatomic bond along the right (R) for WZ and left (L) for ZB. (c, d) Eclipsed (WZ) and staggered (ZB) conformation of atoms. Reprinted with permission from [23], Copyright 1992 by the American Physical Society...

Figure 3.5 Slip caused by the movement of an edge dislocation under a shear stress. At each step (a) to (y), only a small number of interatomic bonds need to be broken.

Periodic variations in the surface tension of liquid metals, c1 , are shown in Figure 6.5. The much higher surface tension of rf-block metals compared to the s- and p-block metals suggests that the surface tension relates to the strength of interatomic bonding. Similar periodic trends can be found also for the melting temperature and the enthalpy of vaporization, and the surface tension of liquid metals is strongly... 

Similarly, surface protonation tends to increase the dissolution rate, because it leads to highly polarized interatomic bonds in the immediate proximity of the surface central ions and thus facilitates the detachment of a cationic surface group into the solution. On the other hand, a surface coordinated metal ion, e.g., Cu2+ or Al3+, may block a surface group and thus retard dissolution. An outer-sphere surface complex has little effect on the dissolution rate. Changes in the oxidation state of surface central ions have a pronounced effect on the dissolution rate (see Chapter 9). 

CN coordination number, R interatomic bond distance, a Debye-Waller factor, AEo. correction of threshold energy and R factor residual factor. 

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