C; at. wt. 12.01115; at. no. 6; valence 4. Stable isotopes: 12 (98.892%); 13 (1.108%); radioactive isotopes: 9-11; 14-16. Abundance in earth's crust: approx 0.027%. Cosmic abundance: 6 atoms/atom Si. Occurs in 3 forms: (1) Diamond, q.v.; (2) Graphite, q.v. or black lead; (3) Amorphous carbon such as coal, lampblack, and the various form of artificial carbon. Comprehensive reviews: P. L. Walker, Am. Scientist 50, 259-293 (June 1962); Holliday et al., Eds. (Pergamon Press, Oxford, 1973) pp 1173-1294; several authors in Kirk-Othmer Encyclopedia of Chemical Technology vol. 4 (Wiley-Interscience, New York, 3rd ed., 1978) pp 556-709.

14C isotope, continuously formed in the earth's atm by the bombardment of nitrogen with cosmic neutrons according to the reaction 147N + 10n 146C + 11H. The 14C is rapidly oxidized to CO2, in this form it penetrates into animals and plants by photsynthesis and metabolism. The 14C content of living matter is estimated at 15.3 disintegrations per minute and per gram of carbon, corresponding to the equilibrium reached between formation of 14C and its exchange with 12C. This equilibrium stops when the plant or animal dies and the 14C content begin to decrease, because the 14C decays with half-life of 5760 years. This fact can be used to date organic matter (not more than 40,000 years old) by comparison with the standard 15.3 disintegration per min per gram: M Haissinsky, J. P. Adloff, Radiochemical Survey of the Elements (Elsevier, New York, 1965) pp 30-32. Production of buckminsterfullerene, a stable cluster of 60 carbon atoms: H. W. Kroto et al., Nature 318, 162 (1985).
Ref.: 1814, 274 pp.
The Merck Index - Eleventh Edition.
Copyright 1989 by Merck & Co., Inc.