Science: No. 97

Medieval man knew of only four elements—earth, air, fire and water. By 1940, scientists knew of 92 elements—ranging from lightweight hydrogen, whose atom has only one electron, to heavy uranium, with 92 electrons. Many chemists thought that their long search for elements was ended, and then the University of California's powerful cyclotron got busy.

Atomic experts bombarded uranium with atomic particles from the cyclotron and produced neptunium, a new "synthetic" element with 93 electrons. Next, Dr. Glenn T. Seaborg and co-workers discovered plutonium (No. 94), and, four years later, at the University of Chicago, americium (No. 95) and curium (No. 96). Last...

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