Selenium physical constants

Some physical constants for selenium are given in Table 1. More extensive data and many sources are available (1 5). For a selenium atom, the covalent radius is ca 0.115 nm, the electron affinity for two electrons is ca —2.33 eV, ie, energy absorbed, and the first ionization potential is 9.75 eV. 

He returned to Upsala, passed his examinations successfully, and was placed m charge of the laboratory. Here, among Berzelius balances, blowpipes, and preparations, he became a true disciple of that great master. After completing some researches on the compounds of selenium, Nilson and Pettersson began to study the mineral euxenite, hoping to measure the chemical and physical constants of the rare earth elements... 

Representative physical constants of selenium and tellurium are listed in... 

Cyclic voltammograms of tetrachalcogenoanthracenes of type (15) all show two reversible one-electron redox waves. Introduction of methyl groups lowers the oxidation potentials. Substitution of tellurium for selenium results in a considerable lowering of both the first and second oxidation potential. The electrochemistry of complexes with TCNQ and analogues of TCNQ is also included <90CL567,91BCJ2091 >, See T ables 1 and 2 for physical constants of donors and complexes with various acceptors. 

The forms and concentration of selenium in the soil solution are governed by various physical-chemical factors expressed in terms of chemical ligands, pH, dissociation constants, solubility products, and oxidation-reduction states. In acid soils (pH 5-6.5), selenium is usually bound as a basic ferric selenite of extremely low solubility and is essentially unavailable to plants. In alkaline soils (pH 7.5-S.5), selenium may be present as selenate ions and become water soluble. 

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