How many naturally occurring elements?
Page 27 claims that there are 92 naturally occurring elements. I have been told that this is incorrect. Apparently the ‘official’ answer to a question in a past HSC paper was that there are 89 atomic numbers 1 to 92, but excluding technetium (At No 43), promethium (61) and astatine (210). The CRC Handbook of Physics and Chemistry claims that there are 91 atomic numbers 1 to 94 less technetium and promethium (and presumably another one). That source claims that both neptunium (At No 93) and plutonium (94) have been found in trace amounts in certain uranium-containing rocks. They are believed to have been formed by reaction of neutrons with uranium in natural transmutation processes. Actually there are several other elements such as francium and astatine which have not strictly been found in nature, but which are conceptually present on Earth. These are elements with only short-lived isotopes that are formed in the radioactive decay series of various naturally-occurring uranium and thori
