ununs

Ununs is a term used in the history of chemical nomenclature to describe a set of temporary systematic names assigned to certain superheavy elements before their discovery was confirmed and permanent names were adopted. The form “unun...” was created as part of an IUPAC naming scheme designed to provide neutral placeholders for elements with atomic numbers beyond the naturally occurring range.

The construction of these names relied on repeating syllables derived from Latin numerals to encode the digits of an element’s atomic number. For example, the late-20th-century placeholder names included ununnilium (110), unununilium (111), ununbium (112), ununtrium (113), ununquadium (114), ununpentium (115), ununhexium (116), ununseptium (117), and ununoctium (118). These terms were intended solely for provisional use in scientific communication until official names could be assigned.

Modern usage and status: beginning in the early 2000s, most of these elements received official names (for example darmstadtium, roentgenium, nihonium, flerovium, moscovium, livermorium, tennessine, and oganesson), and the provisional “unun” names largely faded from formal literature. Today, “ununs” is primarily a historical reference used to illustrate how future elements were named prior to discovery and confirmation, as well as a shorthand in discussions of nomenclature history.

In contemporary pedagogy, the placeholder names are often cited to explain the development of systematic naming conventions and the transition from provisional to permanent element names. See also IUPAC naming, systematic element names, and discovery of superheavy elements.