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Actinides

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The actinide elements (atomic numbers 89 through 103) involve the filling of 5f orbitals. All actinides are radioactive, but only uranium and the lighter actinides have half-lives long enough to be present in Earth's environment. The heavier actinides are produced by nuclear reactions and some have very short half-lives. The actinides also undergo a radius contraction as do the lanthanides with an increasing atomic number. They are characterized by variable oxidation numbers, but the importance of the +3 state and the similarities to lanthanides increase for heavier elements. American chemist Glenn Seaborg is credited with revising the Periodic Table so actinides were placed under lanthanides.

SEE ALSO ACTINIUM; AMERICIUM; BERKELIUM; EINSTEINIUM; FERMIUM; LAWRENCIUM; MENDELEVIUM; NEPTUNIUM; NOBELIUM; PLUTONIUM; PROTACTINIUM; RUTHERFORDIUM; SEABORG, GLENN THEODORE.

Herbert B. Silber

Bibliography

Cotton, Simon (1991). Lanthanides and Actinides. New York: Oxford University Press.