100 Science Discoveries That Changed the World by Colin Salter

Author:Colin Salter
Language: eng
Format: epub
Publisher: Pavilion

On the centenary of his death in 1884, the German Post Office issued a commemorative stamp for Gregor Mendel.

“Mendelian inheritance of the colour of the flower in the culinary pea”, from Breeding and Mendelian Discovery by A. D. Darbishire (London, 1912).

Dmitri Mendeleev

(1834–1907)

The Periodic Table

The driving factor throughout the life of Dmitri Mendeleev was a desire to create order out of chaos. A compulsive organizer and list maker, Mendeleev discovered the Periodic Law and devised the ultimate list, the Periodic Table of Elements.

He was born in the ancient Siberian capital Tobolsk, where his father died when he was thirteen. His mother attempted to reopen the family’s old glass factory, but it burned down a year later and she travelled west across Russia with her youngest, Dmitri, in search of better fortune. They settled in St Petersburg, a world away from Siberia, where Dmitri’s late father had studied and where, in 1850, his mother died. Dmitri Mendeleev turned to science to make sense of his fractured world.

As a teacher at St Petersburg University he solved the problem of a lack of good chemistry textbooks in characteristic fashion, by writing them himself. While writing chapters on the properties of two groups of similar elements – the halogens and the alkali metals – Mendeleev noticed that the atomic weights of the elements within each group were close to each other.

At the time, most attempts to arrange the elements stemmed from the theory of William Prout, an English chemist, that they all developed from the same single source. Most approaches therefore looked more like family trees than lists or tables. Mendeleev, by contrast, believed that each element was unique and connected to others only in compounds.

His attention had been drawn to atomic weights in a paper presented by Stanislao Cannizzaro, an Italian chemist, at a conference a few years earlier. Now it struck him that listing the elements by weight, and therefore properties, might be a good way to organize them for teaching purposes. As he constructed this list, he formulated what he called the Periodic Law: as he put it, that “elements arranged according to the value of their atomic weights present a clear periodicity of properties”. Periodicity means simply sharing similar properties in the same circumstances.

Not content with making his list, Mendeleev then set about presenting the information in diagram form, and came up with the Periodic Table of Elements, which we still use today. It is much larger today than when Mendeleev incorporated the seventy elements then known. But such was the logic of his table that he could use gaps in it to predict the discovery of new elements and their likely properties. When gallium was discovered in 1875, scandium in 1879, and germanium in 1886, the validity of his approach was indisputable.

Mendeleev was twice nominated for the Nobel Prize for chemistry, in 1905 and 1907. Both times he was denied the accolade by behind-the-scenes pressure from Svante Arrhenius, a Swedish scientist who had himself won the prize in 1903 and of whose theories Mendeleev had been critical.

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