Description

One hundred fifty years after Russian chemist Dmitri Mendeleev published his system for neatly arranging the elements, the periodic table it gave birth to hangs in every chemistry classroom in the world and is one of the field’s most recognizable symbols. But the solid squares and familiar patterns of today’s table mask one of its fundamental characteristics: “the” periodic table does not exist.

It’s been mutable from the beginning. Not only has it grown as new elements have been discovered; it has also added columns and changed shape as we’ve gained new understanding of the elements’ properties and their relationships to one another. And scientists are still debating its optimum configuration.

Some believe chemical properties should dictate how the elements line up on the periodic table. Others think a more fundamental principle is needed, like electronic configuration or simply atomic number. Partisans are clashing over which elements belong in group 3, where helium should go, and how many columns the periodic table should have. They follow a long line of chemists and physicists who have worked and reworked the elements into a semblance of order.

“What I find interesting about the current debate is there are people who insist on there being one right table,” says Michael D. Gordin, a Princeton University historian who has written about Mendeleev, Julius Lothar Meyer, and other creators of early periodic tables. “It would have struck people like Mendeleev and Lothar Meyer as weird.” Gordin says the periodic table pioneers understood their tables to be a reflection of natural laws but recognized that different tables could represent those laws in different ways. That might be hard to imagine for those of us used to seeing the familiar shape of the table on our coffee mug or shower curtain.

Setting the table

Mendeleev wasn’t the first to recognize patterns in the elements, nor was he the first to try to depict those patterns in a diagram. Chemist Johann Wolfgang Döbereiner, for instance, identified triads of elements with shared properties in 1829. Today we’d recognize these as members of the same group or column of the periodic table, like chlorine, bromine, and iodine.

Geologist Alexandre-Émile Béguyer de Chancourtois published a kind of periodic table in 1862 in which the elements spiraled up a cylinder according to atomic weight. Each column of elements shared properties.