Primary valency

Alfred Werner. His theory of coordination chemistry was published in 1893 when Werner was 26 years old. In his paper Werner made the revolutionary suggestion that metal ions such as Co3+ could show two different kinds of valences. For the compound Co(NH3)eCI3, Werner postulated a central Co3+ ion joined by "primary valences" (ionic bonds) to three Cl- ions and by "secondary valences"... 

The implications of the foregoing concept have profoundly influenced modern trends in polymer research. If polymers owe their differences from other compounds to the extent and arrangement of their primary valence structures, the problem of understanding them is twofold. It is necessary in the first place to provide appropriate means, both experimental and theoretical, for elucidating their macromolecular structures a[Pg.3]

In spite of the proposals of large primary valence structures for rubber by Pickles and somewhat ambiguously for polybutadiene by Lebedev, prevailing opinion favored rings of moderate size for vinyl and diene polymers. Structures similar to those widely accepted for cellulose and rubber were generally assumed. 

Staudinger relentlessly championed the molecular, or primary valence, viewpoint in the years which followed. He supported his original contentions with the observation that hydrogenation of rubber, as well as its conversion to other derivatives, does not destroy its colloidal properties. In contrast to association colloids, high polymers (or macromolecules as he chose to call them ) exhibit colloidal properties in all solvents in which they dissolve. Polyoxymethylenes were ex-... 

Bonding forces Primary valence forces (intramolecular forces) Secondary valence forces (intermolecular forces)... 

The rapid acceptance of the association theory was accompanied by an equally rapid dropping of the high molecular weight or polymer concept. Olby (31) has stated that three developments made the theory attractive as an explaination for the behavior of polymers. First, he sates, was Alfred Werner s introduction of the concept of two kinds of combining forces—Hauptvalenzen or primary valence forces, and Nebenvalenzen or secondary forces (32). When applied to cellulose, proteins, or rubber, the mole-... 

At the same time K. H. Meyer and Mark (69) proposed an important structure for cellulose which is best described as a compromise between the aggregates of the association theory and Standinger s macromolecules. In an extensive paper, they carefully developed the idea of cellulose chains consisting of so called "primary valence chains". They further proposed that the primary valence chains were aggregated by molecular forces such as hydrogen bonding and van der Waal s forces. 

Their model, which became a standard, combined the important features of both concepts by proposing micelles of long, not short, molecules. The physical properties of cellulose were attributed to these forces, for example, tensile strength to the primary valence bonds and insolubility to the secondary forces. 

From these considerations there evolved the concept of "primary valence chains" in cellulose, held together in bundles, or micelles (crystallites) by secondary forces, as propounded by Meyer and Mark (5). This view was then extended to encompass other high polymers as well. It should be noted however, that Freudenberg had already proposed a chain structure for cellulose, based on degradation experiments (6). If the micelles were to... 

I do not believe that the introduction of primary valence chains, instead of macromolecules, solves any problem." Staudinger also stated these views publicly (29). 

Mark responded to Staudinger on November 2, 1928. Among other things he wrote, "I am sorry to see from your letter that you feel annoyed by the statements of Professor Meyer. I am convinced that it was the last thing Professor Meyer intended to do. I have, in our joint research and especially in my Hamburg lecture, emphasized the importance of your beautiful work. Introduction of the term, primary valence chain, is very purposeful since it refers to structures which are not identical. . . rather average lengths. If we add this fact to your macromolecules, then both concepts become identical. 

In this paper Staudinger objected to the use of "primary valence chains" and micelles. However, he did not exclude the possibility of molecular associations. Although he denied the possibility of micelles, he discussed crystallites. The crystallites and the micelles of Meyer and Mark were identical. 

Usually the reaction mixture also contains unreacted A and/or B. To apply this general reaction scheme to the reaction of polymers, A must be regarded as the reactive group on the macromolecule M. Consequently, the reaction with reagent B yields group C (main product) and group D (by-product) that are likewise bound to the macromolecule by primary valencies hence, in contrast to conversions of low-molecular-weight substances, C and D cannot be separated ... 

In addition to the fundamental core and valence basis described above, one usually adds a set of so-called polarization functions to the basis. Polarization functions are functions of one higher angular momentum than appears in the atom s valence orbital space (e.g, d-functions for C, N, and O and p-functions for H). These polarization functions have exponents ( or a) which cause their radial sizes to be similar to the sizes of the primary valence orbitals... 

The electron density maps need further refinement, but the gross features are distinguishable. These maps show that caffeine and pyrogal-lol alternate in infinite columns parallel to the c axis of the crystal. This association could be characterized as a linear polymer held together by weak (compared with primary valence forces) intermolecular forces. 

Langmuir put forward an extremely definite form of this idea. The adsorbed molecules are supposed to be held to the surface by ordinary valency forces , either primary valencies or secondary valencies . In the light of recent developments in the theory of atomic structure it would probably be sufficient to say that the adsorbed molecules are attached to the molecules constituting the surface by non-polar linkages. Thus the kind of union between tungsten and oxygen adsorbed on its surface, to... 

Werner s terminology ami symbolism differed in small, relatively unimportant ways from that used today. For example. Wcroer referred lo oxidation -state as primary valence Waiipiviilcnc) and coordination number as secondary valence (Nehemulenz) Also, he wrote formulas as Co J A C1 . instead of [CoiNHjljCllClj... 

As a consequence of the fact thal many valence bonds leave residual electrical fields, many molecules in which the "primary" valences are satisfied can combine further with other molecules or with atoms. These higher combinations enter into many important areas of chemical science. They are the basis or the formation of coordination compounds, discussed under that heading. They cause molecular association. They are responsible for the formation of hydrates. They are in many cases Ihe binding forces in nonionic solids, and are of great importance in explaining the structure or larger material aggregates. 

From Table VIII It is seen that tetragonal planar (square) bonds are possible with configurations dsp2 and (rp2. Beside the primary bonds, four strong it bonds are possible, using one p and three d orbitals. In Ni(CN)F% for example, the primary valence configuration of the Ni is dsp so that the structure... 

Chief or primary valency.—Hauptvalenz—which represents those manifestations of chemical affinity which enable the combining capacities (valencies) of the elements to be expressed in terms of hydrogen atoms or tneir equivalents, e.g. Cl—, Na—, N02—, CH3—,. . . The forces emanating from the central atom mainly determine the grouping of the atoms in the central core of complex compounds, although, of course, the mutual attractions of the associated atoms or radicles must be considered. 

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