23/06/2021

Marcelo Viana in Folha: a pop discovery of science.

Crédito: Pixabay

Reproduction of Marcelo Viana's column in Folha de S.Paulo

This year, I gave myself the book "The Mathematics of the Periodic Table" as a birthday present. The periodic table of elements is one of the most iconic discoveries in science. It has left the laboratories and is regularly represented in pop art objects: t-shirts, mugs, towels, and even shower curtains. How could I not be intrigued by the mathematics behind this "stroke of genius in publicity" in chemistry?

The problem dates back to antiquity. The Greek Empedocles (approximately 494 BC–434 BC) believed that all 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. In the following century, chemists sought to understand and classify them.

John Dalton (1766–1844) argued that chemical elements are formed by indivisible particles, which he called atoms. Other substances, he believed, were formed by molecules, composed of atoms of different elements.

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

Alexandre-Émile de Chancourtois (1820–1886) was the first to point out that when elements are listed in increasing order of atomic weight, their chemical properties repeat periodically. Lothar Meyer (1830–1895) noted discrepancies in this law, one of which he sought to explain 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 more than twenty years later and named germanium.

To read the full text, visit the newspaper's website.