22 October 2010
An extended periodic table with 54 predicted elements has been mapped out by a chemist in Finland.
The periodic table of the elements was proposed in 1869 by Dimitri Mendeleev. The value of his scheme for organising the elements was proven by the prediction of the existence and properties of then unknown elements including gallium (first isolated in 1875).
Now Pekka Pyykkö at the University of Helsinki has used a highly accurate computational model to predict electronic structures and therefore the periodic table positions of elements up to proton number 172 - far beyond the limit of elements that scientists can currently synthesise.
The proposed new periodic table for elements
The extra 54 super heavy elements predicted by Pyykkö may exist under extreme conditions with very short lifetimes owing to radioactive decay, but have not yet been synthesised.
Pyykkö says that the value of the work is in showing 'how the rules of quantum mechanics and relativity function in determining chemical properties.' He gives the example of the potentially record-high oxidation states his work predicts.
An expert in electronic structure theory, Peter Schwerdtfeger at Massey University in Auckland, New Zealand, comments: 'chemistry is unthinkable without the periodic table of elements. Pyykkö has used relativistic calculations to go beyond the known elements into unknown territory.'
But he adds that the work in this area is the subject of debate amongst experts who disagree on the placement of certain elements. For atoms with very high nuclear charges, the nucleus could capture an orbiting electron and emit a neutrino causing the proton number to decrease by one.
The debate may only be settled once all the elements have been synthesised but Pyykkö does not expect this to happen anytime soon. 'It is hard to say how far experimentalists will get during this century, maybe close to 130, if not more. Although the experimental results may never appear, the basic physics of the problem are sound,' he concludes.