A pop discovery of science – 06/22/2021 – Marcelo Viana

This year I got myself the book “The Mathematics of the Periodic Table” for my birthday. The periodic table of the elements is one of the most iconic discoveries in science. She left the labs and is regularly featured in pop art objects: t-shirts, mugs, towels, and even bathroom curtains. How could I not be intrigued by the math behind this chemistry “advertising genius”?

The problem goes back to ancient times. The Greek Empedocles (about 494 BC-434 BC) believed that any substance is a combination of four “elements”: earth, water, air, and fire. More than two millennia later, Antoine Lavoisier (1743–1794) listed 33 elements in his “Elementary Treatise on Chemistry” published in 1789. Over the next century, chemists tried to understand and classify them.

John Dalton (1766–1844) argued that chemical elements consist of indivisible particles that he called atoms. The other substances would be made up of molecules made up of atoms of different elements.

Johann Döbereiner (1780–1849) identified “triads” of elements with similar properties, such as lithium, sodium and potassium. Auguste Kekulé (1829–1896) observed that carbon has a valence of four, ie its atoms combine with four hydrogen atoms. Elements of the same triad have the same valence.

Alexandre-Émile de Chancourtois (1820–1886) was the first to point out that the chemical properties of elements, which are sorted according to the increasing weight of their atoms, repeat themselves periodically. Lothar Meyer (1830–1895) noticed deviations in this law, for which he sought an explanation by predicting the existence of an unknown element with an atomic weight of 73 between silicon and tin. This element was identified in the laboratory and named germanium more than twenty years later.

John Newlands (1837–1898) went further in understanding the law of periodicity, pointing out that physical and chemical properties are repeated in eight-element cycles. He believed this was related to the octaves of music, but his “law of octaves” was ridiculed by contemporaries.

The turning point took place in the years 1869–71 with the publication of the tables of elements by Lothar Meyer and above all by the Russian chemist Dmitry Mendeleev (1834–1907). Next week it continues.

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