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1906
Frederick Soddy observes his first examples of chemically identical elements with differing atomic weights, to which he later gives the name isotopes
1913
Albert Einstein formulates the law of photochemical equivalence, a fundamental principle of chemical reactions induced by light
1913
Frederick Soddy uses the term 'isotope' (Greek for 'same place') to describe observed anomalies in the periodic table
1922
Linus Pauling, a graduate student at the California Institute of Technology, begins theoretical work on the nature of the chemical bond
1939
US chemist Linus Pauling publishes his collected discoveries on
The nature of the chemical bond
1945
British chemist Dorothy Hodgkin describes the molecular structure of penicillin
1949
The technique of radiocarbon dating is developed by US chemist Willard Libby
1951
Syntex, a small chemical company in Mexico City, develops the first oral contraceptive
c. 1961
The drug Thalidomide, synthesized in West Germany, is shown to have been the cause of severe defects in about 12,000 children born in 46 countries
2011 August 5
NASA announces that it has photographic evidence from the Mars Reconnaissance Orbiter of possible liquid water on the planet in warm seasons
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