Nature Chemistry | The Sceptical Chymist

A reprieve for Cp?

We’ve been following the story of element 112 and, like many others, have expressed surprise and/or dismay at the proposed name, copernicium, and symbol, Cp – those two letters having a place in many chemists’ hearts for the cyclopentadienyl ligand.

But wait! A letter in this week’s Nature (vol 461, p. 341) from Juris Meija, of the Canadian Institute for National Measurement Standards, suggests that there ‘could be a question mark hanging over’ the use of Cp for element 112.

And this is where it starts to get a little odd…it turns out that IUPAC rules forbid discoverers from proposing names that have previously been suggested and rejected for other elements. Although copernicium hasn’t been proposed for another element, the symbol Cp was associated with cassiopeium, a suggested name for what is now known as lutetium (which as all Asterix fans know, is named after the Latin word, Lutetia, for Paris). Extending the rule a short hop from names to symbols would therefore preclude the use of Cp.

So, rest easy, all those people concerned that they might get confused between the symbols for a widely used 5-carbon-ring ligand and a newly discovered artificial element of which a whole 3 atoms have ever existed on earth


Neil Withers (Associate Editor, Nature Chemistry)


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    T. P. Radhakrishnan said:

    There has been considerable debate about the symbol for the new element copernicium. The choices would heirarchically be: Co, Cp, Ce, Cr, Cn … and in terms of contributions from the syllables, it would be Cp, (Cr), Cn … . As Co, Ce and Cr (Cobalt, Cerium, Chromium) are already in, and Cp runs into a number of difficulties including the common usage for cyclopentadienyl anion, the natural choice should be: Cn ! Choice of the second letter in the symbol from so far down in the name (6th letter) is not common of course, but certainly not unprecedented; take the cases of Cm, Pd (both 6th), Rf, Tm (both 7th).

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    T. P. Radhakrishnan said:

    Carolinium and Berzelium were names proposed for what were thought to be new elements supposedly isolated from a mixture with thorium (J. Am. Chem. Soc. 1904, 26, 922; Science 1904, 19, 892). It was subsequently found to be a case of mistaken identity; there was only thorium present and not a mixture. Cn does not exist in the present day periodic table. Unless IUPAC (est. 1919) has considered and rejected it, Cn should qualify as a viable symbol for Copernicium; Cc is not bad either, but then, Cc is a popular crystallographic space group!

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    Francesco Neve said:

    The previous comments move all along the direction set by the discoverers of element 112. I would like to suggest a shift toward an alternative name.

    Since Copernicus was a Polish scientist, I would suggest the IUPAC to consider the possibility to name the element according to the polish version of the name (i. e. Kopernik).

    Since there is no element as Ko or Kp, this could settle the quarrel.