Lanthanides Definition in Chemistry

Below the main body of the periodic table are two rows of elements. These are the lanthanides and the actinides. If you look at the atomic numbers of the elements, you'll notice they fit in the spaces below scandium and yttrium. The reason they aren't (usually) listed there is because this would make the table too wide to print on paper. Each of these rows of elements has characteristic properties.

The lanthanides are generally considered to be elements with atomic numbers 58-71 (lanthanum to lutetium). The lanthanide series is the group of elements in which the 4f sublevel is being filled. All of these elements are metals (specifically, transition metals). They share several common properties.

However, there is some dispute over exactly where the lanthanides begin and end. Technically, either lanthanum or lutetium is a d-block element rather than f-block element. Yet, the two elements share characteristics with other elements in the group.

The lanthanides are indicated by the chemical symbol Ln when discussing general lanthanide chemistry. The group of elements actually goes by any of several names: lanthanides, lanthanide series, rare earth metals, rare earth elements, common earth elements, inner transition metals, and lanthanoids. The IUPAC formally prefers the use of the term "lanthanoids" because the suffix "-ide" has a specific meaning in chemistry. However, the group acknowledges the term "lanthanide" predates this decision, so it is generally accepted.

The lanthanides are:

• Lanthanum, atomic number 58
• Cerium, atomic number 58
• Praseodymium, atomic number 60
• Neodymium, atomic number 61
• Samarium, atomic number 62
• Europium, atomic number 63
• Gadolinium, atomic number 64
• Terbium, atomic number 65
• Dysprosium, atomic number 66
• Holmium, atomic number 67
• Erbium, atomic number 68
• Thulium, atomic number 69
• Ytterbium, atomic number 70
• Lutetium, atomic number 71

All of the lanthanides are shiny, silver-colored transition metals. Like other transition metals, they form colored solutions, however, lanthanide solutions tend to be pale in color. The lanthanides tend to be soft metals that can be cut with a knife. While the atoms can exhibit any of several oxidation states, the +3 state is most common. The metals are generally quite reactive and form an oxide coating upon exposure to air. Lanthanum, cerium, praseodymium, neodymium, and europium are so reactive they are stored in mineral oil. However, gadolinium and lutetium only slowly tarnish in air. Most lanthanides and their alloys quickly dissolve in acid, ignite in air around 150-200 °C, and react with halogens, sulfur, hydrogen, carbon, or nitrogen upon heating.

Elements of the lanthanide series also display a phenomenon called lanthanide contraction. In lanthanide contraction, the 5s and 5p orbitals penetrate into the 4f subshell. Because the 4f subshell is not fully shielded from the effects of the positive nuclear charge, the atomic radius of the lanthanide atoms successively decreasing moving across the periodic table from left to right. (Note: This is, in fact, the general trend for atomic radius moving across the periodic table.)

Lanthanide minerals tend to contain all elements within the series. However, the vary according to the abundance of each element. The mineral euxenite contains lanthanides in nearly equal proportions. Monazite contains mainly lighter lanthanides, while xenotime contains mostly heavier lanthanides.

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