Spedding, Frank H. Formerly, Ames Laboratory, Energy Research and Development Administration, Iowa State University, Ames, Iowa.
- Links to Primary Literature
- Additional Readings
The name given to an unusual phenomenon encountered in the rare-earth series of elements. The radii of the atoms of the members of this series decrease slightly as the atomic number increases. Starting with element 58 in the periodic table, the balancing electron fills in an inner incomplete 4f shell as the charge on the nucleus increases. According to the theory of atomic structure, this shell can hold 14 electrons; so starting with element 58, cerium, there are 14 true rare earths. Lanthanum has no electrons in the 4f shell, cerium has 1, and lutetium, 14. The 4f electrons play almost no role in chemical valence; therefore, all rare earths can have three electrons in their valence shell and they all exist as trivalent ions in solution. As the charge on the nucleus increases across the rare-earth series, all electrons are pulled in closer to the nucleus so that the radii of the rare-earth ions decrease slightly as the compounds go across the rare-earth series. Any given compound of the rare earths is very likely to crystallize with the same structure as any other rare earth. However, the lattice parameters become smaller and the crystal denser as the compound proceed across the series. This contraction of the lattice parameters is known as the lanthanide contraction. For many compounds the lattice parameters decrease only partway across the series, and when the contraction has progressed to that point, a new crystalline form develops. Frequently, both crystalline forms can be observed for a number of the elements. For this reason, the rare-earth series is of particular interest to scientists because many of the parameters determining the properties of a substance can be kept constant while the lattice spacings can be varied in small increments across the series.
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Its dedicated editorial team is led by Sagan Award winner John Rennie. Contributors include more than 9000 highly qualified scientists and 42 Nobel Prize winners.
MORE THAN 8500 articles and Research Reviews covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 17,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information