Lanthanides (old name)

IUPAC currently recommends the name lanthanoids rather than lanthanides. The suffix "-ide" generally indicates negative ions whereas the suffix "-oid" indicates similarity to one of the members of the containing family of elements.

The fourteen elements of the upper row on the inner-transition metals on the periodic table that follow the element lanthanum (#57). Some reference sources include lanthanum in this series others do not. For all of these elements the filling orbital is 4f. This series is a sub-series of the transition metals.

All lanthanides closely resemble lanthanum, hence the name. They are shiny and silvery-white, and tarnish easily when exposed to air. They react violently with most nonmetals. They are relatively soft but their hardness increases with their atomic number. Lanthanides burn in air and they have high melting and boiling points.

Most lanthanides are widely used in lasers. These elements deflect UV and infrared electromagnetic radiation and are commonly used in the production of sunglass lenses.

The ionic radii of the lanthanides decrease through the period - the so-called "lanthanide contraction". Except for cerium (III and IV) and europium (III and II), the lanthanides occur as trivalent cations in nature.