The Nature of Bonding in Solids

In a few substances, known as network covalent solids, covalent bonds extend throughout a crystalline solid. In these cases, the entire crystal is held together by strong forces. Consider, for example, two of the allotropic forms in which pure carbon occurs—diamond and graphite. 

Types Particles tributing Forces Typical Properties Examples 

Metallic Cations and delocalized electrons Metallic bonds Hardness varies from soft to very hard melting point varies from low to very high lustrous ductile malleable very good conductors of heat and electricity Na, Mg,Al, Fe, Sn, Cu, Ag, W 

Ionic Cations and anions Electrostatic attractions Hard moderate to very high melting points nonconductors as solids, but good electric conductors as liquids many are soluble in polar solvents such as water NaCl,MgO, NaNOs 

Network covalent Molecular Atoms Covalent bonds Most are very hard and either sublime or melt at very high temperatures most are nonconductors of electricity C(diamond), C(graphite), SIC,AlN,Si02 

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As we have noted above and will see in more detail later, the pair potential description is littered with difficulties. There are a few directions which can be taken that will be seen to cure some of them. We begin with a qualitative discussion of these issues, and turn in what follows to the development of both angular force schemes and effective medium theories that patch some of these troubles, primarily through the device of incorporating more of what we know about the nature of bonding in solids. 

The Nature of Bonding in Solids 12-6 Crystal Structures 12-7 Energy Changes in the Formation of Ionic Crystals... 

The Nature of Bonding in Solids—Solids can be classified according to the nature of bonding. In network covalent solids chemical bonds extend throughout a crystalline structure. For these substances the chemical... 

The nature of bonding in oxides changes across any period in the periodic table (see Figure 15.8). Oxides of elements on the left side of the periodic table, such as those of the alkali metals and alkaline earth metals, are generally ionic solids with high... 

A nice example, which is still a matter of debate, is the nature of bonding in the simplest organometalhc compound, methyllithium. In the solid state it forms tetramers [Li4(CH3)4] (Figure 10.43), which are further linked into a three-dimensional network. Related aggregates are found for other alkyl lithium compounds. The distances within these tetramers are Li-Li 2.588 A and Li-C 2.256 A. Both values are well below the sum of radii of the pairs used in automated routines to draw bonds between close lying atoms ( bond(C) = 0.77, rbond(Li) = 1 -52 A, plus an allowance of 0.25 A added for each atom). Such automated... 

The nature of bonding in the carbides is known to be a mixture of covalent and metallic with little ionic tendency. If solid solutions were formed, Ta from TaSi substimted the transition metal atoms in the carbide lattice. This may occur either by cations diffusion or by solntion-precipitation. Given the low diffusion coefficient of this class of materials, it is presumed that lattice diffusion can occur only at very high temperature. Indeed, solution re-precipitation seems to be the dominant mechanism, in light of the sintering behaviour characterized by a relatively low T, 1400-1600°C (Table 2). The well-defined boundary between core and shell and the morphology of the interface between them also put forward a re-precipitation from liquid phase over a diffusion process. 

The initial set of experiments and the first few textbook chapters lay down a foundation for the course. The elements of scientific activity are immediately displayed, including the role of uncertainty. The atomic theory, the nature of matter in its various phases, and the mole concept are developed. Then an extended section of the course is devoted to the extraction of important chemical principles from relevant laboratory experience. The principles considered include energy, rate and equilibrium characteristics of chemical reactions, chemical periodicity, and chemical bonding in gases, liquids, and solids. The course concludes with several chapters of descriptive chemistry in which the applicability and worth of the chemical principles developed earlier are seen again and again. 

Energy is needed to break the ionic bonds in the solid salt and energy is liberated forming hydration complexes like VI. We also break some of the natural hydrogen bonds in the water. The overall change in enthalpy is termed the enthalpy of solution, A// olutioni. Typical values are —207 kJmol-1 for nitric acid 34 kJmol-1 for potassium nitrate and —65.5 kJmol-1 for silver chloride. 

The nature of the anion can play a part in determining the mode of bonding in the solid state. Thus the complex cation [Pd(CNS)(Et4dien)]+ has an N-bonded thiocyanate ligand in its most stable form when SCN- is the counterion,73 but when PF or BPhiT are the counterions the stable isomer in the solid state has S-bonded thiocyanate ligands.75,76... 

Section 4 is entirely devoted to ferroelectric and H-bonded systems. It also provides a nice illustration of results that always maintained the utility of proton NMR in solid state, even wideline, or how the old question of the order disorder or displacive nature of some ferroelectric phase transitions were reopened by progresses in NMR resolution. A number of structural phase transition is discontinuous, but the examples of coexistence in solid-state and kinetic studies are rather scarce this is the object of Section 5. Section 6 is devoted to single-crystal studies that allow very precise comprehension of subtle phase transition mechanisms. Section 7 introduces the salient features of NQR that represent an interesting alternative to NMR in some cases. The section ends with a table of miscellaneous phase transitions that complete the references given in the text. Section 8 concludes and presents some perspectives in NMR phase transition studies. 

This is a classic treatment of the nature of bonding between atoms. It discusses extensively bonding in molecules but there is also a rich variety of topics relevant to the bonding in solids. 

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