When the French chemist Paul-Émile Lecoq de Boisbaudran in 1875, the examined minerals from the Pyrenees, he discovered a new element, a metal which he named gallium after Gaul, the roman name for France. He presented his discovery, but soon got a letter that urged him to investigate the substance density again because he probably had measured wrong. de Boisbaudran did so, and found that the sender of the message, the Russian chemist Dmitry Mendeleyev, was right. The density was not the 4.7 grams per cubic centimeter – which he first had presented – without is 5.9 grams per cubic centimeters, almost exactly the value that Mendeleyev had predicted.
“It was what made Mendelejevs table more widely known,” says Michael Gordin, professor of modern and contemporary history at Princeton University and the author of the book ”A Well-Ordered Thing: Dmitrii Mendeleev and the Shadow of the Periodic Table”.
Link to the graphics
, in February 1869. Dmitry Mendeleyev was writing a textbook on chemistry in the two bands. Part one was already finished. The book’s 500 pages is about the four elements: carbon, oxygen, hydrogen and nitrogen. In the last chapter describes the Mendeleyev the so-called the halogens – fluorine, chlorine, bromine and iodine – a group of substances with very similar properties. They react, for example, easily with metals to form salts, like sodium chloride, i.e. common table salt.
Tape the two of you would be equally thick. But of the 63 known elements, he had just gone through eight in the first part.
– He had 55 subjects who would get a spot in volume two, in the same space. So he tries to find a way to arrange them so that he can describe them as economically as possible, ” says Michael Gordin.
start to think about alkalimetallerna: lithium, sodium, potassium, and rubidium. All is soft and light metals, which react violently with water and gives alkaline solutions, i.e. solutions with a high pH-value. When he compares their atomic weight or atomic mass, which is a measure of how much an atom of a substance weighs, he discovers that the difference between the two alkali metals is very similar to the difference between the two halogens.
– He starts to believe that maybe there is something natural system which explains why it is like this, ” says Michael Gordin.
There are several widespread myths about how Dmitri Mendeleyev came up with the periodic system, as he had a deck of cards with the formation of chemical elements properties of the cards, and that he got the key insight in a dream. But it is not true, according to Michael Gordin. In Mendelejevs leftover paper is seen instead clearly how he step by step builds up a table, where he proceeds from the halogens and alkalimetallerna and then try to get all the other elements to fit in the right place.
, and renskriver a manuscript to send to the printer. It is dated the 17th of February 1869, which means the march 1, 1869, since Russia had not yet switched over to the gregorian calendar. Dmitry Mendeleyev, type a title in Russian and French: ”An attempt at classification of the elements based on their atomic weight and chemical affinity” (about their propensity to react with other substances). Then, he changes himself, and wiped the classification and type system instead, but fail to change the French article ”une” for classification (feminine) to ”un” système (masculine).
– So it is a typo on the very first printed version of the periodic table, Michael Gordin.
was not so similar to the periodic system, which now hangs on the wall in each kemiklassrum in the whole world. But his idea was correct, and the breakthrough was so significant that the UN general assembly and Unesco has designated the 2019 to the international year of the periodic system, in order to celebrate the 150-year anniversary.
the most noteworthy is the fact that Mendeleyev could not know the basics that the table looks the way it does. The topics are arranged according to their atomic number, i.e. the number of protons in the nucleus of the atom. But the designation was created by the british physicist Henry Moseley in 1913, six years after the Mendelejevs death. In which column a substance ends up is determined by how the electrons are arranged in the atom’s outermost electron shell, but the electron was first discovered in 1897, J. J. Thomson, another british physicist.
Mendeleyev was very suspicious of electrons, and was not sure he believed them. And he knew it guaranteed nothing about quantum mechanics. Niels bohr’s formulation of the periodic system in terms of kvantorbitaler came in 1923, says Michael Gordin.
realized Dmitry Mendeleyev that there was at least three blanks in his table. When he is in 1871 published an improved version he had given them a name: eka-boron, eka-aluminum and eka-silicon, where the eka ”one” in sanskrit. He also gave very detailed predictions about their properties and how they could be detected. It was why he was so confident in the Boisbaudran had measured galliums density wrong, because all the other properties correspond to eka-aluminium. Then discovered scandium in 1879 and germanium in 1886.
– in particular, germanium tallied remarkably well with eka-silicon. When it was discovered it was a brilliant success for the system, and it did Mendeleyev to the world, ” says Michael Gordin.
