Lewis Dartnell - Elemental: the periodic table at 150

This year marks the 150th anniversary of the publication of the first periodic table. This grid-like arrangement of the elements is probably only familiar to most of us from the tatty poster hanging on the wall of the chemistry classroom at school – only slightly less memorable than the faint background of weird smells in the lab. But when the Russian chemist Dmitri Mendeleev laid out his vision for ordering the chemical world in 1869, it was revolutionary.

This is because the periodic table is far more than just a list of the elements we know. It’s a way of categorising and sorting them: finding the order in the mess of chemical reactions. The startling realisation was that there is a repeating pattern – a periodicity – in the properties of the elements, such as how they react with each other. (We know now that fundamentally this comes down to how the electrons in an atom, which determine how it behaves, fit into successive shells around the nucleus.) 

The known elements can be laid out into rows and columns, with those lining up in the same column sharing characteristics, like a chemical family. Neon, argon and xenon, for example, all have similar properties: they are the noble gases and are exceedingly reluctant to be cajoled into any reactions. And when electricity is passed through a tubeful, they emit garish colours; the lights that became synonymous with Las Vegas and other urban centres.

Mendeleev’s flash of insight (he later claimed to have seen his whole grand construct in a dream) also allowed him to infer the existence of as yet undiscovered elements – holes in the brickwork of known elements – and even to predict their properties. He postulated that “ekaaluminium” must exist in the gap in his table immediately below aluminium; we now know this as gallium, and his forecasts on its properties were spot on.

Mendeleev had only 61 known elements at the time to sort, but by the early years of the 20th century we had identified 85 of these fundamental building blocks of the universe, all falling neatly into place in the framework... read more:

https://www.theguardian.com/science/2019/feb/02/elemental-periodic-table-at-150-mendeleev-system-vital-modern-life-smartphones-gallium-indium-helium