Residual valences

Staudinger, like Pickles in 1910, chemically modified rubber and noted its failure to lose colloidal properties as evidence of chain structure (49). His experimental proof was impressive for he had catalytically hydrogenated natural rubber and then thoroughly studied the properties of the saturated product. He reasoned that the disappearance of the double bonds of natural rubber should result in a loss of "residual valence", and failure to do so was conclusive. 

The ethylene addition product is saturated, that of benzene, on the other hand, is more unsaturated than is benzene itself, since the symmetrical cancelling of residual valency (Thiele) is upset and the aromatic character is destroyed. In order to re-establish this character it is only necessary for hydrogen bromide to be eliminated, which takes place with liberation of energy. The elimination occurs with extraordinary speed, even before the other double bonds, which have become reactive, have time to take up bromine. 

Some general comments on the solid-state chemistry ( From a molecular view on solids to molecules in solids ) have been reported by Simon (1995) emphasis was especially placed on the structural chemistry of metal-rich compounds formed by the metals in groups 1 to 6 and it was underlined that it is largely based on discrete and condensed clusters. In the chemistry of metals in low oxidation states, the residual valence electrons can be used for metal—metal bonding. Metal-rich compounds lie between normal valence compounds and the elemental metals themselves, with respect to their compositions, and often also with respect to their structures fragments of usual metal structures (close-packed, b.c.c., etc.) are often component units in the structures of metal-rich compounds. 

Adsorption can be divided into two types. Chemical adsorption results in the formation of a monomolecular layer of the adsorbate on the surface through forces of residual valence of the surface molecules. Physical adsorpbon results from molecular condensation in the capillaries of the solid. In general, substances of the highest molecular weight are most easily adsorbed [27]. 

F.Ephraim, Ber 46, 3103-31(1913) CA 8, 597 (1914) (The nature of residual valence influence of the anion on the stability of complex cations in metal ammonia compds) 7)... 

The nature of residual valence of zinc ammines. Table in Ber 48, p 646 gives ealed values for absol tcrr ps of dissociation and... 

Figure 11-1 Left Schematic representation of a nickel crystal in cross section showing residual valences at the surface atoms. Right Adsorption of ethene on the surface of the nickel crystal with formation of C-Ni bonds.

Step 1. Adsorption of hydrogen molecules. Hydrogen molecules are adsorbed on the nickel surface due to the residual valence bonds of the nickel atoms. 

The nature of the bonds forming molecular addition compounds has been investigated by several workers, but up to now it has not been made sufficiently clear. Pfeiffer [112] held that complex formation was due to the mutual saturation of residual valencies , but Briegleb [113,114] advanced the theory that addition compounds should be regarded as polarization aggregates which owed their stability to electrostatic interactions, possibly due to polarization of one component by the other. Thus, in the case of polynitro compounds, their strongly polar mole cules influence the non polar molecules of the hydrocarbon. Further, no covalent bonds exist between these two kinds of molecules. This hypothesis has received considerable support and a new development. 

Two layer sets, ideally [LaS] and [CrS2] (the latter for Cr " "), display large residual valencies but, from the imprecisely known substructures, no firm conclusions can be drawn about the details of site occupation or local valency imbalance within the layers. 

The free valence index was proposed as a measime of the residual valency of the ith atom in Ji-electron molecular orbitals [Coulson, 1946] it is defined as ... 

In a cyclic system such as benzene, all residual valences could be mufiisffiy satisfied, explaining the remarkable inertness of aromatic compounds. In benzene, Thiele proposed a complete redistribution of bonds, leading to a regular hexagon structure ... 

Around 1900, two new theories were developed Thiele 8> suggested that in a double bond the valencies of the atoms could not be incompletely used and that the residual valencies could interact with each other, as shown in formulas (1) (2) (3)... 

Admittedly the cellulose molecule is very much larger than cellobioee and the question is now under discussion as to whether it is a pole-merized molecule held together by strictly primary valences or whether it is a colloid molecule of the general type suggested by Langmuir and held together by secondaiy or residual valences. ... 

Reactivity of strongly bonded molecules was considered by Thiele [60], who introduced the concept of residual valence. This is tied in with Bayer s strain theory in the sense that a solution for the same question was sought. Whereas the stereochemistry of the cycloalkanes made Bayer s theory obsolete, the later introduction of resonance more or less confirmed Thiele s intuition. 

Coordination compounds are formed by the union of two or more compounds which are themselves stable and capable of independent existence. Some of them dissociate on heating, but others are extremely stable. Examples of coordination compounds are NH3BF3 (Experiment 15), A(BF3)2, Fe(CO)6, Co(NH3)3(N02)3, and ionized salts such as Cu(NH3)4S04 (Experiment 5), K4Fe(CN)6, the hundreds of cobaltammines, NH4CI, and H2SiFe. These compounds were a puzzle to the older theories of valence, since their formation seemed to involve residual valences or valences in excess of the normal valences of the atoms concerned. Today, however, they are believed to be bound by means of the coordinate link, which is simply a special kind of covalent bond. 

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