Central forces shell model

In the bond charge model, the effect of the metal-like binding is described by central forces between nearest-neighbour ions while the covalent bonding is described by interactions involving the BC s [4.51,52]. In the adiabatic bond charge model of WEBER [4.17,18], the constraint that the BC s are fixed on the midway positions between the atoms is removed. Instead, they are allowed to move adiabatically like the electronic shells in the shell... 

In fact, there is little reason to believe that s, p, and d orbitals really do exist in the outer shells of many bonded atoms. Remember that these different orbitals arise in the first place from the interaction of the electron with the central electrostatic force field associated with the positive nucleus. An outer-shell electron in a bonded atom will be under the influence of a force field, emanating from two positive nuclei rather than one, so we would expect the orbitals in the bonded atoms to have a somewhat different character from those in free atoms. We can, in fact, throw out the concept of atomic orbital altogether and reassign the electrons to a new set of molecular orbitals that are characteristic of each molecular configuration. This approach is indeed valid, but we will defer a discussion of it until later. For now, we will look at a less-radical model that... 

Figure 45(d) shows the determination of the tensile strength of model agglomerates by means of the wall friction method.For this test a cylindrical pellet—sometimes with a central pin—is produced in a press. After removing the specimen from the press, it is stressed directly in the die shell. The tensile force is transmitted by adhesion between the end surfaces and the pistons as well as on the circumference and the die walls. Again, the tensile strength is defined by the quotient rupture force P divided by the cross section of the cylindrical or ring-shaped sample. 

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