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The Epic Interactive Encyclopedia 1998
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Epic Interactive Encyclopedia, The - 1998 Edition (1998)(Epic Marketing).iso
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Lanthanide
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1992-09-03
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Any of a series of 15 metallic elements (also
known as rare earths) with atomic numbers 57
(lanthanum) through 71 (lutetium). One of its
members, promethium, is radioactive. All
occur in nature. Lanthanides are grouped
because of their chemical similarities (they
are all bivalent), their properties differing
only slightly with atomic number. They were
called rare earths originally because they
were not widespread and were difficult to
identify and separate from their ores by
their discoverers. The series is set out in a
band in the periodic table of the elements,
as are the actinides.