In the early nineteenth century, a chemist called Amedeo Avagadro suggested that equal volumes of gases held at the same pressure and temperature must contain equal numbers of molecules.
The notion languished for several decades until it was revisited enthusiastically in 1860 at an annual chemical congress in Karlsruhe, Germany. One of the attendees was a fierce and imposing young Russian called Dmitri Mendeleev. It was a collision of idea and intellect that was to have a profound impact on the practice of science.
Avagadro’s theory implied that elements could be weighed, and that the weight of each – assuming identical conditions – would always be consistent.
It was the germ of an organising principle for chemistry that was desperately needed. By the time of the congress, some 70 elements had been identified, but how they related to each other remained largely a matter of guesswork.
That Mendeleev picked up the idea and wrestled with it was a mark of the ferocious determination that marked his life and work. He was born in Toblosk – a city and Tsarist gulag in Siberia – in 1836, the youngest of an estimated 16 children. The exact number has never been conclusively determined.
Medeleev’s father was a philosophy teacher, but shortly after Dmitri’s birth he was struck blind and forced to retire, leaving the family in penury. When he died not long after, it fell to his widow – a Siberian native called Marya – to support the brood, which she did by reopening an abandoned glass factory.
She was undoubtedly a tough woman, but also a remarkably caring one. When teachers told her that young Dmitri was exceptionally clever, she immediately travelled with him to St Petersburg and secured him a place at the city’s Chief Pedagogical Institute – the finest school in the region. She died soon after.
After surviving a bout of tuberculosis, Mendeleev went on to teach at St Petersburg University before moving to Germany and undertaking further study in Heidelberg. He returned to St Petersburg in 1867, fascinated by Avagadro’s idea.
He set about exploring it methodically, weighing each element and noting the result on pieces of card, to which he added any other pertinent information, such as the appearance of the material, and apparent mathematical relationships with others.
Gradually, a pattern began to emerge. Elements with very similar weights were revealed to have very similar physical properties.
Others has similar appearances but quite widely ranged weights, and this turned out to be crucially important. Mendeleev suggested that such gaps indicated the presence of other elements, still to be discovered. Not all his predictions were on the money: but many were, confirmed by discoveries in subsequent decades.
Thus, the Periodic Table came into being. Today, it contains 118 elements, but it rests very firmly on the principles determined by its inventor.
As well as this achievement, Mendeleev also penned a seminal text book, Principles of Chemistry, which remained a standard work, translated into many languages, for decades. He also played a key role in developing Russia’s Black Sea petroleum industry.
His fame spread around the world and in 1876 he was invited to the US. He hated the place, considering it backward.
Mendeleev married twice – at one stage, because the Orthodox Church refused to grant him a divorce, having two wives. He appealed to the Czar, who overruled the bishops.
Late in life he switched his attention from chemistry to art, becoming a noted critic and collector. In his final years he was affected, like his father, with cataracts, losing his sight. He died in January 1907.
Andrew Masterson is a former editor of Cosmos.
Read science facts, not fiction...
There’s never been a more important time to explain the facts, cherish evidence-based knowledge and to showcase the latest scientific, technological and engineering breakthroughs. Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science. Financial contributions, however big or small, help us provide access to trusted science information at a time when the world needs it most. Please support us by making a donation or purchasing a subscription today.