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02 February 2016

Mendeleyev: Playing Cards with Chemistry

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The last row of the periodic table has just been completed, with the announcement of four new elements (with the numbers 113, 115, 117 and 118), although they don’t yet have names or symbols. One of the last elements to officially receive them was number 112, named copernicium (Cn) in February 2010 in honor of astronomer Nicolaus Copernicus, fourteen years after German scientists created a single atom of this artificial and extremely radioactive element, which disintegrated before it could be studied carefully.

Long before that, it was already known that if one day we were able to collect trillions of atoms of copernicium, it would form a metal, since this element had a place reserved for it just below zinc, cadmium and mercury in the Periodic Table —ever since it was created in the nineteenth century by Dmitri Mendeleev, a Russian chemist also famous because his name appears on millions of bottles of vodka.

Mendeleev in 1897

Mendeleev did not find it easy to succeed in science. In 1849, when he was 15, his family lost everything in a fire and his mother decided to take him to St. Petersburg so he could continue his studies. They had to cross Russia to get there, more than 6,000 kilometers from his native Siberia, which had not yet been reached by the railroad, so they hitchhiked. His mother died shortly after fulfilling her goal and leaving Mendeleev enrolled at school. That same year, the writer Fyodor Dostoyevsky made the same route but in reverse: he had been deported to Siberia. Both men went on to have brilliant careers in St. Petersburg, where Mendeleev’s lectures at the university became very popular.

Hundreds of students flocked to hear this loud and flamboyant man, who accepted women among his students, and who only cut his beard and hair once a year. But he was not a showman. It was just that he gave very entertaining classes without following a textbook —partly because there was no elementary treatise on chemistry in Russian. When he set out to write one, he also decided to solve the problem of the disorder of the elements.

Monument to the periodic table in Bratislava, Slovakia. Credit: MMMDIRT

He wrote the data for each element on a card and locked himself in his office to arrange them. First, he put the elements in order of the weight of their atoms. Another possibility was to group them with cards of similar elements. Then he realized that he could combine the two rules and, with his deck of cards of the 63 elements that were known at that time, he did something similar to the game solitaire, with the atomic weight increasing in each row and the elements with similar properties lined up in columns. The German chemist Lothar Meyer had done the same —without either of them knowing of the other’s work— but Mendeleev finished a year earlier, in 1869, and was more daring than Meyer. He changed the position of elements that didn’t fit well because of their weight, and he left gaps open for undiscovered elements, for which he predicted their properties and atomic weights.

It wasn’t that he was practicing card reading for chemistry. His predictions were based on observing that the properties of the elements were repeated periodically in each row, hence the name Periodic Table.

Soviet Union’s stamp (1969)

Within just ten years, three elements were discovered that fit the predictions of Mendeleev (gallium, scandium and germanium) and the scientific world surrendered at his feet. Even Tsar Alexander II forgave him his political rebellion and even his bigamy, a result of his second marriage (illegal) with a young art student: “It is true, Mendeleev has two wives, but I have only one Mendeleev.” In addition, the czar commissioned him to start up the first Russian oil wells and according to the legend he also established that vodka with officeal label must contain 40% alcohol by volume, the ideal strength for maximizing its flavour according to what Mendeleev had calculated in his doctoral thesis. But this is a myth, born from the marketing of the vodka brand Russian Standard. The most famous russian chemist never studied vodka and the 40% standard strength was introduced in 1843, when he was only 9 years old.

When he passed his heyday, Mendeleev became a controversial scientist. He was furious with his colleagues who favoured new ideas such as the existence of the electron, which Mendeleev refused to accept. But understanding the inside of atoms (including the electron and other particles) more clearly served to consolidate his periodic table, which is now ordered not by the weight of the atoms but by the number of protons. When, in 1955, element 101 was named mendelevium, to many it seemed very appropriate that it was an unstable element.

By Francisco Doménech for Ventana al Conocimiento

@fucolin

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