August 29, 2019 1:31:42 pm
By Siobhan Roberts
When Sir Martyn Poliakoff, a chemist at the University of Nottingham, heard about a game called Periodic Table Battleship, he couldn’t help but imagine a player’s perspective of the opponent’s inverted fleet of elements.
This catalyzed a mad idea. In May — coinciding with UNESCO’s International Year of the Periodic Table, which marks its 150th anniversary — Poliakoff and collaborators, including his daughter, Ellen Poliakoff, an experimental psychologist at the University of Manchester, published a paper with a recommendation: “Turning the Periodic Table Upside Down.”
“Since 1869, generations of chemists have proposed variations in format to improve the table, to make it clearer or just to make it more fun,” they wrote.
The iconic periodic table of elements, devised by Russian chemist Dmitry Mendeleev, is a two-dimensional array of the chemical elements, ordered by atomic number and arranged 18 across by orbitals. It presents a schema of patterns and trends that enables scientists to predict elemental properties, reactivities and even new elements. It has been called “nature’s Rosetta Stone,” “the chemist’s map” and “probably the most compact and meaningful compilation of knowledge yet devised.”
“Much like if I look at a map of the United States, and I’m in Maine, I can tell that the temperatures there are going to be lower than if I were in Florida,” Gregory Girolami said in a joint interview with his wife, Vera Mainz. Both are inorganic chemists at the University of Illinois at Urbana-Champaign. With Carmen Giunta, a chemist at Le Moyne College in Syracuse, they organized a 150th anniversary symposium, held this week during the American Chemical Society’s national meeting in San Diego.
“If you tell me an element is in a certain place,” Girolami said, “I can tell you lots of things about it — whether it’s a metal or not, whether it is abundant on Earth or not — simply by noting its location in the periodic table.”
Mainz added, “If you want to communicate with an alien race, put up a periodic table.”
The Internet Database of Periodic Tables lists more than 1,000 versions, including a table of elemental scarcity, as well as cupcake, clock, Lego and haiku variations, and more technical adaptations. Mathematician and musician Tom Lehrer set it to music (by Gilbert and Sullivan), and Italian chemist, writer and Auschwitz survivor Primo Levi used it as the basis for an idiosyncratic memoir (“The Periodic Table”).
“Many people seem to believe that there is only one true periodic table, either that exists or is waiting to be discovered, and they go to great lengths to debate the validity of the different types,” said Poliakoff, who is a YouTube personality with his Periodic Videos. “My feeling is that most types are equally valid, and it just depends what you are trying to show.”
The upside-down version aimed to show the value of a fresh perspective. “We are not claiming that our version is in any way ‘more correct’ than the traditional table,” the authors wrote.
Why Not Alphabetical?
The periodic table brought solidity to a field of inquiry that had long been squishy. Sir Isaac Newton, in Query 31, a section in his 1717 work “Opticks,” listed and ranked chemical compounds according to their reactivity. In 1718, the first “affinity table” by French chemist Étienne François Geoffroy ranked the reactivity of materials in graphical form. Close observers of nature noted that certain chemical elements like lithium, sodium and potassium — known today as alkali metals — were all soft and floated in water. But such qualitative classifications offered only a shaky foundation.
The breakthroughs began in 1860 when Stanislao Cannizzaro, an Italian chemist, grounded the discussion of atomic weight. There had been conflicting lists of atomic weights circulating and varying assumptions about what constituted an atom versus a molecule. Cannizzaro produced a list of the atomic weights of the known elements, along with a rationale for the values, which he handed out as a pamphlet at a conference in Karlsruhe, Germany.
“That opened the door for what I like to call the simultaneous discovery by six individuals, over a period of about seven years, culminating in Mendeleev,” said Eric Scerri, a historian and philosopher of science at the University of California, Los Angeles, and an expert on the history of the periodic table. (An updated edition of his book “The Periodic Table: Its Story and Significance” will be published in October by Oxford University Press.) In 1862, French geologist Alexandre-Émile Béguyer de Chancourtois produced a three-dimensional table, inscribing elements around a metal cylinder. John Newlands, a sugar chemist in London, arranged elements in order of atomic weight, in groups of eight.
“It was laughed at and dismissed,” Scerri said.
British chemist William Odling discovered the “periodic law” — properties of a family of elements that repeat, approximately, at regular intervals. Gustavus Hinrichs proposed a radial ordering. “I call it the bicycle-wheel periodic table,” Scerri said.
Lothar Meyer, a German chemist, created a partial periodic table in 1864 and a more complete version in 1869. “Structurally, Meyer and Mendeleev’s tables were very similar,” said Alan Rocke, a science historian at Case Western Reserve University, who gave a talk about Meyer at the ACS anniversary symposium.
Initially, the table’s periodicity and predictive powers seemed like a “numerological mystery,” Rocke said. In the 20th century, the periodicity was explained by quantum physics — specifically, the physics of how electrons orbit the nucleus. Lithium, sodium and potassium, which nicely align in the table’s first vertical column — Group One, the alkali metals, with rubidium, cesium and francium — all have one electron in their outer electron shell.
Both chemists constructed many tables over many years, tweaking them in response to new discoveries and better data. Eventually Mendeleev’s won out. When gaps emerged in the patterns of his tables, he made predictions about what should appear. Some were wrong, but he accurately foretold the existence of three elements: gallium, germanium and scandium.
“Prediction is psychologically dramatic,” Scerri said. “If a scientist predicts something and it comes true, there is a sense in which that scientist knows the secrets of nature or almost knows the future.”
But science rarely advances by revolution, Scerri said: “Science is an activity carried out by hundreds of thousands of researchers all contributing to the general picture that eventually emerges.”
📣 The Indian Express is now on Telegram. Click here to join our channel (@indianexpress) and stay updated with the latest headlines