Actinides

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 A CTINIUM ; A MERICIUM ; B ERKELIUM ; E INSTEINIUM ; F ERMIUM ; L AWRENCIUM ; M ENDELEVIUM ; N EPTUNIUM ; N OBELIUM ; P LUTONIUM ; P ROTACTINIUM ; R UTHERFORDIUM ; S EABORG , G LENN T HEODORE .

Herbert B. Silber

Bibliography

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