lanthanoids

Lanthanoids, or lanthanides, are a group of fifteen metallic elements with atomic numbers 57 through 71, spanning from lanthanum (La) to lutetium (Lu). They are f-block elements whose chemistry is largely governed by the progressive filling of the 4f electron subshell. Most lanthanoids exhibit a predominant +3 oxidation state in their compounds, though cerium and some others can display +4 under certain conditions and a few can show +2 in specific cases.

They occur together in minerals such as monazite and bastnäsite and are not found free in nature. Economic production involves mining these minerals and then employing complex separation techniques, including ion-exchange and solvent extraction, to distinguish adjacent lanthanoids despite their very similar chemistries.

Physically, lanthanoids are silvery-white, relatively soft metals that tarnish in air and form oxides readily. Across the series, they display a lanthanide contraction, a gradual decrease in ionic radii that influences bonding, coordination chemistry, and trends in physical properties. The chemistry of the series is highly similar, which historically made their separation challenging and drove the development of advanced separation technologies.

Applications are widespread: phosphors containing europium and cerium are used in lighting and displays; neodymium and samarium contribute to strong permanent magnets; cerium oxide serves as a catalyst and in petroleum refining; various lanthanides are used in glass and ceramic formulations to adjust optical and physical properties. The lanthanoids are an integral part of modern materials science, electronics, and energy technologies, and they are typically considered together as a distinct block of the periodic table within the broader group of inner transition metals.