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Families of Element

The Lanthanides And Actinides

The lanthanides (or rare-earth elements) and actinides are two families that are related because they both result from electrons being added into an f sub-level. Both families have 14 members, the lanthanides consisting of the elements with atomic numbers 58 through 71, and the actinides including the elements with atomic numbers 90 through 103. However, it is sometimes convenient to consider lanthanum (atomic number 57) as an honorary member of the lanthanide family and to treat actinium (atomic number 89) in a similar manner with respect to the actinides.

The lanthanides are usually found together in the same ores and despite their alternative name of the rare-earth elements, they are not particularly rare. In contrast, only two of the actinides, thorium and uranium, occur in nature, the remainder having been synthesized by nuclear scientists. Members of both families form ions with a charge of +3, although other ions are also formed, particularly by the actinides.



Emsley, John. Nature's Building Blocks: An A-Z Guide to the Elements. Oxford: Oxford University Press, 2002.

Norman, Nicholas C. Periodicity and the s- and p-Block Elements. Oxford Chemistry Primers, no. 51. New York: Oxford Univ. Press, 1997.

Silberberg, Martin. Chemistry: The Molecular Nature of Matter and Change. St. Louis: Mosby, 1996.

Arthur M. Last


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—The ability of identical atoms to bond together to form long chains or rings.


—Elements in the same group of the periodic table.

Diatomic molecule

—A molecule consisting of two atoms.

Electron configuration

—The arrangement of electrons in the occupied electron energy levels or sub-levels of an atom.

Main-group elements

—Those elements in groups 1, 2 and 13 through 18 of the periodic table.

Principal quantum number

—An integer used to identify the energy levels of an atom.


—A group of three elements displaying a certain regularity in their properties.

Valence electrons

—The electrons in the outermost shell of an atom that determine an element's chemical properties.

Additional topics

Science EncyclopediaScience & Philosophy: Electrophoresis (cataphoresis) to EphemeralFamilies of Element - The Search For Patterns Among The Elements, The Main-group Families, The Transition Metals - Hydrogen: The elemental orphan, Other families of elements