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Elementary stuff: the wonders of the periodic table, first created 150 years ago

The original 7 Up included a compound of lithium, used to medicate mood swings

Two scientists use a massive, illuminated periodic table of elements as they discuss the element holmium in the Lawrence Hall of Science at the University of California, Berkeley. Photograph: Ted Streshinsky/Corbis via Getty Images

Fri Jun 14 2019 - 06:20

One of the most amazing scientific discoveries of the last two centuries was created using nothing more than a pen and a piece of paper by Dmitri Mendeleev in 1869: the periodic table. He was fascinated by atomic theory – the idea that chemical elements are uniquely defined by their atomic make-up.

Matter was known to be made up of elements, of which 62 had been identified. Mendeleev tried to capture these in a single diagram, laying them out in a long row. The eureka moment came when he realised that there were patterns within the row: elements with similar properties (how reactive they were, whether they were metals and so on) cropped up at specific “periods” within it.

By chopping up the row and rearranging it in shorter rows with similar elements above each other, he came up with the first version of the periodic table.

The Periodic Law
Mendeleev's "periodic law" stated that these patterns were part of the essential nature of the elements. For instance, his left-hand column included sodium, lithium and potassium, all solids at room temperature which tarnish easily and react explosively when mixed with water (don't try this at home!).

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Mystic Mendeleev
Astonishingly, the gaps in Mendeleev's table (especially once it had been rearranged by atomic number rather than mass) predicted the existence of elements that hadn't been discovered at the time. Elements such as scandium, germanium and gallium were later identified, with the exact properties the table predicted them to have. We have now identified all 118 elements, the basic stuff of everything in the cosmos.

Unknown artist’s portrait of Dmitri Ivanovich Mendeleyev (1834-1907), the Russian chemist best known for his work on the periodic law, at work in his laboratory. Photograph: Time Life Pictures/Mansell/The LIFE Picture Collection/Getty Images

Inflammable Air
Hydrogen is the simplest, most common element. It is present in huge quantities on our planet, but it is highly reactive, so almost always found compounded with other elements: with oxygen it forms water, and it is part of hydrocarbons in fossil fuels such as crude oil. It was only discovered in the late 18th century, when Henry Cavendish noticed that a gas he had isolated produced water when it burned. He believed in the now discredited phlogiston theory, which suggested that all combustible bodies contained a fire-like element and became "dephlogisticated" when they burned, so he called hydrogen "dephlogisticated air" or "inflammable air".

The Strange Case of 7 Up
Most people know that Coca-Cola originally contained cocaine, but did you know the original version of 7 Up included a compound of the metal lithium, lithium citrate (also used to medicate mood swings)? The Howdy Corporation, founded by Charles Leiper Grigg, launched "Bib-Label Lithiated Lemon-Lime Soda in 1920. The name was eventually changed to 7 Up: however, it became illegal to include lithium in beverages in 1948.

The Mickey Mouse Effect
After helium was found in US natural gas deposits, the first helium production plant (supplying the army with gas for barrage balloons) opened in 1915 in Texas. From 1919 the US navy experimented with gas mixes to combat the dangers of nitrogen narcosis in deep sea divers. In one experiment, divers breathing a helium and oxygen mixture complained that their high-pitched voices had hampered communication. (The comical squeakiness is caused by soundwaves, which travel faster in any gas that is lighter than air.)

The Yellow Death
Fluorine is a halogen (along with chlorine, bromine, iodine and astatine, all highly reactive and potentially lethal). Fluorine is a dangerous pale yellow gas – a concentration of air containing just 0.1 per cent fluorine will be fatal within minutes, and a stream of the gas aimed at solids such as bricks or glass will make them spontaneously combust. A well-known compound is polytetrafluoroethene, a daunting name for the substance better known by the trademarked name Teflon. It was accidentally discovered in 1938 in the DuPont laboratories, during research into new types of refrigerants, after the cooling gas left a residue of white powder behind in cylinders it was stored in.

The Crimson Light
Neon is a great example of how Mendeleev's work inspired chemists to hunt down elements. Sir William Ramsay had already discovered other members of the group of unreactive "noble gases", including helium, krypton and argon, but the periodic table predicted one more. By repeatedly freezing and then evaporating air, they finally succeeded in isolating a tiny amount of neon, which gave off an astonishing crimson glow when burned. It was that brilliant red light which inspired George Claude to create neon lamps, which would become hugely successful after being marketed by the Claude Neon company.

The Missing Element
For a long time, no one could identify element 43 from Mendeleev's table, for the simple reason that it doesn't exist on Earth. Now known as "technetium", it is mainly formed in nuclear reactions in stars, but is radioactive with a short half-life, so any left on our planet would long ago have decayed into other elements. When the Italian scientists Carlo Perrier and Emilio Segrè isolated two isotopes of a new element on a piece of molybdenum foil that had been bombarded at the particle accelerator in Berkeley, it took well over a decade for their colleagues to accept that this method of creating an "artificial" element was legitimate, and to recognise their discovery.

The Blue Meanies
Cobalt was first isolated by the Swedish chemist Georg Brandt in 1735 – although he had to convince sceptical colleagues it wasn't merely a compound of iron. He named it after the German word kobold, which means goblin, because German mineworkers hated ores that contained the metal, which they sometimes mistook for silver – the high melting point made it impossible to work with, but it released toxic arsenic fumes when heated, so they regarded it as an evil goblin's trick.

Kryptonite Discovered!
In the 2006 movie Superman Returns, the chemical formula for kryptonite (Superman's nemesis) is given as 'sodium lithium boron silicate hydroxide with fluorine'. This is remarkably close to the mineral jadarite, which was discovered a year later - although those scientists who whipped up mass media attention by claiming that the 'real' kryptonite had been found should have noted that the new mineral didn't contain fluorine and, it certainly didn't glow with an eerie green light. So, close, but no cigar!
Elementary by James M Russell is published by Michael O'Mara Books