Hydrogen variable atomic weight

Hydrogen as it occurs in nature is predominantly composed of atoms in which the nucleus is a single proton. In addition, terrestrial hydrogen contains about 0.0156% of deuterium atoms in which the nucleus also contains a neutron, and this is the reason for its variable atomic weight (p. 17). Addition of a second neutron induces instability and tritium is radioactive, emitting low-energy particles with a half-life of 12.33 y. Some characteristic properties of these 3 atoms are given in Table 3.1, and their implications for stable isotope studies, radioactive tracer studies, and nmr spectroscopy are obvious. 

This book presents a unified treatment of the chemistry of the elements. At present 112 elements are known, though not all occur in nature of the 92 elements from hydrogen to uranium all except technetium and promethium are found on earth and technetium has been detected in some stars. To these elements a further 20 have been added by artificial nuclear syntheses in the laboratory. Why are there only 90 elements in nature Why do they have their observed abundances and why do their individual isotopes occur with the particular relative abundances observed Indeed, we must also ask to what extent these isotopic abundances commonly vary in nature, thus causing variability in atomic weights and possibly jeopardizing the classical means of determining chemical composition and structure by chemical analysis. 

Amphoteric property a-amino acid 1.0, aminobenzoic acid 0.5, pyridinecarboxylic acid 0.5 Dummy variable for the presence of p-lactam Summation of numbers of carbon and halogen atoms weighted by C, 1.0 F", 0.5 Cl, I.O Br, 1.5 and 1, 2.0 Dummy variable for the presence of intramolecular hydrogen bonds as ortho-OH and —CO—R, —OH and NH,... 

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