Sir

There could be a question mark hanging over the symbol proposed for the newly recognized element 112, copernicium (Nature 460, 449; 2009).

According to the current recommendations of the International Union of Pure and Applied Chemistry on naming new elements, a candidate name cannot be reused on another element (W. H. Koppenol Pure Appl. Chem. 74, 787–791; 2002). For example, the names hahnium or joliotium can no longer be considered for any as-yet unnamed element, because both were once used to name element 105, which is now called dubnium.

If this rule is formally extended to symbols of elements, it will affect the proposed symbol (Cp) for copernicium. This symbol was used for element 71, cassiopeium, before that was formally named lutetium (F. A. Paneth Nature 159, 8–10; 1947).

With C, Ce, Cm, Co, Cr and Cu already taken, Ci short for curie as a unit of radioactivity and Cp open to debate, a 'clean' option for copernicium could be the unprecedented Cc.