Lanthanides Properties and Elements

Properties of Element Groups

Neodymium is an example of a lanthanide element.
Neodymium is an example of a lanthanide element.

The lanthanides or D Block elements are a set of elements of the periodic table. While there is some dispute over which elements to include in the group, the lanthanides generally include the following 15 elements:

  • Lanthanum (La)
  • Cerium (Ce)
  • Praseodymium (Pr)
  • Neodymium (Nd)
  • Promethium (Pm)
  • Samarium (Sm)
  • Europium (Eu)
  • Gadolinium (Gd)
  • Terbium (Tb)
  • Dysprosium (Dy)
  • Holmium (Ho)
  • Erbium (Er)
  • Thulium (Tm)
  • Ytterbium (Yb)
  • Lutetium (Lu)

Here is a look at their location and common properties:

Key Takeaways: Lanthanide

  • The lanthanides are a group of 15 chemical elements, with atomic numbers 57 through 71.
  • All of these elements have one valence electron in the 5d shell.
  • The elements share properties in common with the first element in the group -- lanthanum.
  • The lanthanides are reactive, silver-colored metals.
  • The most stable oxidation state for lanthanide atoms is +3, but the +2 and +4 oxidation states are also common.
  • Although the lanthanides are sometimes called the rare earths, the elements are not particularly rare. However, they are difficult to separate from one another.

The D Block Elements

The lanthanides are located in block 5d of the periodic table. The first 5d transition element is either lanthanum or lutetium, depending on how you interpret the periodic trends of the elements. Sometimes only the lanthanides, and not the actinides, are classified as rare earths. The lanthanides are not as rare as was once thought; even the scarce rare earths (e.g., europium, lutetium) are more common than the platinum-group metals. Several of the lanthanides form during the fission of uranium and plutonium.

Lanthanide Uses

The lanthanides have many scientific and industrial uses. Their compounds are used as catalysts in the production of petroleum and synthetic products. Lanthanides are used in lamps, lasers, magnets, phosphors, motion picture projectors, and X-ray intensifying screens. A pyrophoric mixed rare-earth alloy called Mischmetall (50% Ce, 25% La, 25% other light lanthanides) or misch metal is combined with iron to make flints for cigarette lighters. The addition of <1% Mischmetall or lanthanide silicides improves the strength and workability of low alloy steels.

Common Properties of the Lanthanides

Lanthanides share the following common properties:

  • Silvery-white metals that tarnish when exposed to air, forming their oxides.
  • Relatively soft metals. Hardness increases somewhat with higher atomic number.
  • Moving from left to right across the period (increasing atomic number), the radius of each lanthanide 3+ ion steadily decreases. This is referred to as 'lanthanide contraction'.
  • High melting points and boiling points.
  • Very reactive.
  • React with water to liberate hydrogen (H2), slowly in cold/quickly upon heating. Lanthanides commonly bind to water.
  • React with H+ (dilute acid) to release H2 (rapidly at room temperature).
  • React in an exothermic reaction with H2.
  • Burn easily in air.
  • They are strong reducing agents.
  • Their compounds are generally ionic.
  • At elevated temperatures, many rare earths ignite and burn vigorously.
  • Most rare earth compounds are strongly paramagnetic.
  • Many rare earth compounds fluoresce strongly under ultraviolet light.
  • Lanthanide ions tend to be pale colors, resulting from weak, narrow, forbidden f x f optical transitions.
  • The magnetic moments of the lanthanide and iron ions oppose each other.
  • The lanthanides react readily with most nonmetals and form binaries on heating with most nonmetals.
  • The coordination numbers of lanthanides are high (greater than 6; usually 8 or 9 or as high as 12).

Lanthanide Versus Lanthanoid

Because the -ide suffix is used to indicate negative ions in chemistry, the IUPAC recommends members of this element group be called lanthanoids. The -oid suffix is in keeping with names of another element group -- the metalloids. There is a precedent for a name change, since an even earlier name for the elements was "lanthanon." However, nearly all scientists and peer-reviewed articles still refer to the element group as the lanthanides.

Sources

  • David A. Atwood, ed. (19 February 2013). The Rare Earth Elements: Fundamentals and Applications (eBook). John Wiley & Sons. ISBN 9781118632635.
  • Gray, Theodore (2009). The Elements: A Visual Exploration of Every Known Atom in the Universe. New York: Black Dog & Leventhal Publishers. p. 240. ISBN 978-1-57912-814-2.
  • Holden, Norman E.; Coplen, Tyler (2004). "The Periodic Table of the Elements". Chemistry International. IUPAC. 26 (1): 8. doi:10.1515/ci.2004.26.1.8
  • Krishnamurthy, Nagaiyar and Gupta, Chiranjib Kumar (2004). Extractive Metallurgy of Rare Earths. CRC Press. ISBN 0-415-33340-7
  • McGill, Ian (2005) "Rare Earth Elements" in Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim. doi:10.1002/14356007.a22_607