Some Physical Properties of the Covalent Link

Some Physical Properties of the Covalent Link in Chemistry, by N. V. Sidg-... 

In 1931, Sidgwick joined the faculty of Cornell University as the George Fisher Baker Non-resident Lecturer. At Cornell, he decided to lecture on the covalent link in chemistry, focusing on the physical methods used to measure the more important properties of those bonds, such as heats of formation, dimensions, and electric dipole moments. His lectures were later published in the book Some Physical Properties of the Covalent Link in Chemistry (1933). 

Sidgwick, N. V. 1933. Some physical properties of the covalent link in chemistry. New York Cornell University Press. 

Methods can be based on some preconceived concept of bonding, with ionic and covalent extremes, or on pattern recognition based on the periodic table. Miscellaneous methods of limited applicability link bond strength with other physical properties. The a priori calculation of heats of formation by wave mechanics is possible in theory. In practice, the most widely applied method incorporates experimental data to derive atom or bond parameters which can then be used for calculations on closely related compounds. 

Yet another development of remarkable nanostmctured materials yields superlattices of nanosized objects. As there is no dear distinction between molecular crystals and superlattices formed from nanopartides, at this point reference will be made to structures composed of very similar (but most likely not exactly identical) nanopartides, namely colloidal partides in the size range 2 to 10 nm. Two excellent reviews by leading experts in the field were produced in 1998 and 2000 [19, 20], the titles of which contained the terms nanocrystal superlattices and close-packed nanociystal assemblies. These are in line with the above-outlined delimitation, although Collier et al. have also reported on molecular crystals (as above). The two reviews comprised approximately 100 pages with some 300 references, and summarized the state of the art at that time in exemplary fashion. The topics induded preparative aspects of the formation of monodisperse nanopartides of various compositions including metals, the superlattice formation itself with some theoretical background, covalent linking of nanocrystals (see below), and an appropriate description of the physical properties and characterization of the nanocrystal superlattices. 

BirGfring6nC6 of Polymer Networks. Elastomeric polymer networks deserve special mention because their cross-linked structure gives them unique physical properties, unlike those of other polymers. Covalently bonded networks are insoluble in any solvent, even in those that dissolve their precursor polymers. Optical techniques such as strain-induced birefringence allow the development of structure-property relationships as well as the study of their optical properties. Here we review some of the classical theories as well as some of the latest developments in the field. 

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