The iconic periodic table could have looked very different. On its 150th anniversary, a chemist looks back at the various tables we almost ended up with.

Pedro_P

Theodor Benfey’s spira table (1964).
DePiep/Wikipedia
▼ The periodic tablestares down from the walls of just about every chemistry lab. The credit for its creation generally goes to Dimitri  Mendeleev, a Russian chemist who in 1869 wrote out the known elements (of which there were 63 at the time) on cards and then arranged them in columns and rows according to their chemical and physical properties. To celebrate the 150th anniversary of this pivotal moment in science, the UN has proclaimed 2019 to be the International year of the Periodic  Table.

John Dalton’s element list.
Wikimedia Commons
But the periodic table didn’t actually start with Mendeleev. Many had tinkered with arranging the elements. Decades before, chemist John Dalton tried to create a tableas well as some rather interesting symbols for the elements (they didn’t catch on). And just a few years before Mendeleev sat down with his deck of homemade cards, John  Newlandsalso created a table sorting the elements by their properties.
Mendeleev’s genius was in what he left out of his table. He recognised that certain elements were missing, yet to be discovered. So where Dalton, Newlands and others had laid out what was known, Mendeleev left space for the unknown. Even more amazingly, he accurately predicted the properties of the missing elements.

Dimitry Mendeleev’s table complete with missing elements.
Wikimedia Commons
Notice the question marks in his table above? For example, next to Al (aluminium) there’s space for an unknown metal. Mendeleev foretold it would have an atomic mass of 68, a density of six grams per cubic centimetre and a very low melting point. Six years later Paul Émile Lecoq de Boisbaudran, isolated galliumand sure enough it slotted right into the gap with an atomic mass of 69.7, a density of 5.9 g/cm³ and a melting point so low that it becomes liquid in your  hand. Mendeleev did the same for scandium, germanium, and technetium(which wasn’t discovered until 1937, 30 years after his death).
At first glance Mendeleev’s table doesn’t look much like the one we are familiar with. For one thing, the modern table has a bunch of elements that Mendeleev overlooked (and failed to leave room for), most notably the noble gases (such as helium, neon, argon). And the table is oriented differently to our modern version, with elements we now place together in columns arranged in rows. (▪ ▪ ▪)

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dushazmi

Periodic table reminds me of Nightmare of old days.