Valence satisfaction

The difference 0.24 A between the O—H distance in this compound and in water corresponds to bond number 0.40 (Equation 7-7). Accordingly the formation of a symmetrical hydrogen bond permits the satisfaction of the valence of the oxygen atom. 

In our description of the metal structures we have, of course, included many in which covalent or ionic binding predominates. Such systems may often quite properly be regarded as chemical compounds, but it is not in such systems that the chief interest lies, and here we shall discuss only the systems of more pronouncedly metallic character, including the electron compounds. It was early pointed out by Hume-Rothery that if formulae are assigned to such phases they must not be expected to obey the ordinary chemical valencies of the metals concerned. In fact, the satisfaction of chemical valencies is the negation of metallic properties... 

The data seem to confirm the idea that atoms of identical size and valency can be substituted for one another with much less disturbance1 than occurs when either the atomic diameters or the valencies are different. The most favourable condition for wide solid solution is. therefore, that the atoms should be of nearly the same size and that they should have the same number of outer-layer or valency electrons. It must, however, be noted that the satisfaction of the latter condition does not, of necessity, mean that the metals concerned must belong to the same periodic table group. In fact, continuous solid solubility docs occur in manv hinar alloys of the transitional elements with one another and with tin1 elements of (Jroup 111 copper, silver and gold—provided, of course, that the size-factors are... 

In the semiconducting alloys, on the other hand, ideality of structure, i.e., local satisfaction of valence requirements, implies that the connectivity of the network varies locally as the valence of the constituents vary. Thus, in addition to the translational disorder of the elements and compounds, there is compositional disorder at the nodes of the network and additional translational disorder associated with the randomness of connectivity. This increased disorder could broaden the tails until they overlap, (Cohen (1969)) as shown in Figure 3.5. Such overlapping may also be the case for some liquid semiconductors because of their reduced short-range order. The... 

Thus, the anion 0 has the valence 2 to be satisfied, from the cations combinations of Table 4.18, according to the Rule 2. Yet, the possible combinations are reduced to a single one, for the requirement of the satisfaction of the Rule 5, so that each anion to be surrendered by the same cations combination in Table 4.18 there results the coordination illustrated in Figure 4.74. 

The studies of Kroto, Smalley and coworkers (at Rice University) showed that carbon nanotubes constitute a particular case of the fullerene family. The most famous and most stable of the fullerene molecules is C60, with a computer-simulated image very similar in appearance to a soccer ball. This molecule consists of 20 hexagonal and 12 pentagonal faces, with the carbon atoms at each corner of the individual polygons. C60 stability has been attributed to the pentagon rule and the satisfaction of all valences when the pentagon faces lead to the closure of individual C60 molecules. 

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