Valences secondary

The atoms of a molecule are held together by primary bonds. The attractive forces which act between molecules are usually referred to as secondary bonds, secondary valence forces, intermolecular forces or van der Waals forces. 

The term secondary valency has been superseded by the term coordination number . This may be defined as the number of donor atoms associated with the central metal atom or ion. For many years a distinction was made between coordination number in this sense and in... 

TPEs are materials that possess, at normal temperatures, the characteristic resilience and recovery from the extension of crosslinked elastomers and exhibit plastic flow at elevated temperatures. They can be fabricated by the usual techniques such as blow molding, extrusion, injection molding, etc. This effect is associated with certain interchain secondary valence forces of attraction, which have the effect of typical conventional covalent crosslinks, but at elevated temperatures, the secondary... 

Cleanness of the base, i.e. freedom from grease, which improves the wettability of the metal surface, and the removal of oxides, dust or loose paint, etc. already described. The closer the surfaces of paint film and metal, the more secondary valencies originating in the polar constituents of the medium are brought into play. 

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"... 

Moreover, he made the inspired guess that the six secondary valences were directed toward the corners of a regular octahedron. 

These results indicate clearly the usefulness of the CP/MAS NMR method in analysing the structure of secondary valence bonds in polymers by using relaxation T1 data. Similarly useful data may be obtained by the Tip parameter. 

Nylon fibers are semicrystalline, that is, they consist of crystallites separated by amorphous regions. Hydrogen bonding is an important secondary valence interaction in nylon-6 and nylon-6,6. Individual chains in the microcrystalline regions of nylons are held together by hydrogen bonds. Nylons are resistant to aqueous alkali but deteriorate more readily on exposure to mineral acids. 

Photolysis in acetonitrile gives ortho- (10) andpara-phenylbenzaldehyde (11), as well as cis- (12) and fmws-diphenylstilbene (13). The mechanism for product formation is not clear, but the norcaradiene valence isomer is thought to be the most likely precursor, arising either via a secondary... 

Again, remember that coordination number is equivalent to Werner s secondary valence. 

Other treatments " have led to scales that are based on different principles, for example, the average of the ionization potential and the electron affinity, " the average one-electron energy of valence shell electrons in ground-state free atoms, or the compactness of an atom s electron cloud.In some of these treatments electronegativities can be calculated for different valence states, for different hybridizations (e.g., sp carbon atoms are more electronegative than sp, which are still more electronegative than and even differently for primary, secondary,... 

A second factor of importance in this connection is found in the emphasis which was placed in the 1890 s and early 1900 s on secondary association of molecules. Coordination complexes, the concept of partial valences, and van der Waals forces attracted wide attention... 

Reversible gels which are dispersible on heating and are soluble in excess. These have secondary valence or ionic bonds... 

If the work function is smaller than the ionization potential of metastable state (see. Fig. 5.18b), then the process of resonance ionization becomes impossible and the major way of de-excitation is a direct Auger-deactivation process similar to the Penning Effect ionization a valence electron of metal moves to an unoccupied orbital of the atom ground state, and the excited electron from a higher orbital of the atom is ejected into the gaseous phase. The energy spectrum of secondary electrons is characterized by a marked maximum corresponding to the... 

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