lanthanoid

The lanthanoids are a group of 15 chemical elements with atomic numbers 57 through 71, from lanthanum to lutetium. They form the f-block of the periodic table and are commonly discussed together with the rare earth elements. The term is often used interchangeably with lanthanides, though some sources differ on whether lanthanum is included in the series.

They are silvery, soft metals that occur naturally in minerals and are generally reactive. The most common oxidation state is +3, but some elements exhibit +2 or +4 under certain conditions. Their chemistry is strikingly similar across the series because the 4f electrons are shielded by outer electrons. A lanthanide contraction causes a gradual decrease in ionic radii from lanthanum to lutetium, influencing bonding and magnetic properties.

Lanthanoids occur together in mineral deposits such as monazite and bastnasite. Extraction and purification require complex separation because the elements have very similar chemical properties. Separation typically proceeds via solvent extraction and ion-exchange methods to isolate individual elements, followed by refining to the metallic state.

Applications of the lanthanoids are widespread in modern technology. Permanent magnets based on neodymium and samarium are essential in electronics and wind turbines. Many lanthanoids serve as catalysts in petroleum refining or as polishing powders. Doped phosphors (for example Eu2+, Tb3+, Ce3+) are used in lighting, displays, and scintillators. They also color glasses and ceramics and are used in certain laser materials, such as Nd:YAG.

Note on terminology: Lanthanoid and lanthanide are widely used for the same group, though definitions vary on whether lanthanum is included in the series.