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Such has been the scientific and cultural impact of Dmitri Mendeleev’s periodic table of the elements that many people assume it is essentially complete. In its 150th year, can researchers simply raise a toast to the table’s many dividends, and occasionally incorporate another heavy synthetic element?

No — this invaluable compilation is still not settled. The placements of certain elements, even hydrogen and helium, are debated. Chemists dispute certain groupings, such as which elements should form group three of the periodic table (see Traditionalists maintain that these comprise scandium, yttrium, lanthanum and actinium; a growing number thinks that lutetium and lawrencium should replace the last two on the basis of electronic structures. This matters, because moving an element to a different group might reveal new properties — it could become a candidate for inclusion in a high-temperature superconductor, for example.

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