lanthanide

The lanthanides, also known as the lanthanoid elements, form a series of 15 metallic elements in the periodic table, with atomic numbers from 57 (lanthanum) to 71 (lutetium). They are f-block elements, and their chemistry is dominated by the gradual filling of the 4f subshell. In most compounds they exhibit a +3 oxidation state, although cerium and terbium can reach +4, and europium and ytterbium can show +2 under certain conditions.

Chemically, the lanthanides display high coordination numbers and form oxides and halides that are typically stable and often colorless in solution. Their 4f electrons are well shielded, resulting in similarities across the series and the well-known lanthanide contraction: a progressive decrease in ionic radii from Ce to Lu. This contraction affects bond lengths and reactivity, and it influences the separation and purification of the elements.

Occurrence and production: lanthanides occur together in minerals such as bastnasite and monazite and are recovered from mineral concentrates by complex separation processes, including solvent extraction and ion-exchange techniques, due to their very similar chemistries.

Applications: the elements are essential in modern technology. They are used in permanent magnets (neodymium, samarium), phosphors for lighting and displays (europium, terbium, cerium, gadolinium), catalysts, and various high-tech materials. Some isotopes have niche uses in medicine or research.

Naming and classification: while commonly grouped as a single series, some sources debate whether lanthanum is a true lanthanide or a member of the d-block; however, La is routinely included in the lanthanide series. The term comes from the Greek lanthanein, meaning to lie hidden.