Most people know the the Periodic Table was designed by a certain Russian fellow, Dmitri Ivanovich Mendeleev. What most people don’t know is that the story of how he got there is a crazy story of alchemy, magic, science, pseudo-science and playing cards.
Throughout history, mankind has played God with chemicals. Back in the Bronze Age, we were mining the right kinds of metals and mixing them to make something new. And before that we’ve been mixing flour and water to make basic forms of bread and other food types. And we’ve also had ideas that there are fundamental chemicals that make up the universe – the Greeks famously thought the entire universe was made of the 4 elements Earth, Water, Air and Fire.
But as time (and human understanding) progressed, it became clear that there were more than just these 4. There were a few natural substances – mostly metals – that seemed unique but couldn’t be broken down by chemical reactions. Some of these are the base metals – gold, silver, copper, iron and mercury. Others are the elements that it’s easiest to isolate – like hydrogen and carbon. There were just enough of these for there not to be a natural pattern, and too few to find any sort of complex pattern. But as more and more elements were discovered and the golden age of chemistry began to dawn, people needed a pattern. It was the Industrial Revolution, for crying out loud. Man had to impose order on the chaos of nature. The quest was on – to design a table of the elements.
The problem with designing the Periodic Table was simple. Today, we know a lot about atoms. We know about electron shell structure (to be covered later), atomic weights and atomic number (also to be covered later). But in the 1800s, not a lot was known. Jöns Jacob Berzelius (a Swedish chemist) was working through the atomic weights of all the known elements. But those are only so useful – we now know that there are different forms of pure elements, each with different weights (called isotopes). Atomic weights are a good starting point, but they can only get you so far.
One of the first actual attempts to find a pattern was from German chemist Johann Wolfgang Döbereiner. He found some patterns in the atomic weights of certain elements – his Law of Triads. He found that certain groups-of-threes elements had a pattern – the middle of the three had an atomic weight that was the mathematical mean of the other two.
In other words, take the triad lithium, sodium and potassium. Lithium has an atomic mass of 6.9, potassium is 39.1. Those of you who are fast on the calculators will find that the mean of those two is 23. The mass of sodium is 23. Ta da!
There were just a few problems with Döbereiner’s triads. They only worked on a few select groups, so you couldn’t predict any atomic weights with it. And there is a key point. Without a way to organise the elements, you can’t work out which elements form a triad without trial and error. And that would take ages even with the few elements known of then. Today it would take days of manual calculation.
Side note: I wrote a hasty Python script that did what I just described with 118 elements. I don’t claim it to be 100% efficient and I did only run it on one core of a crappy old laptop, but it was a good tool for simulating how long this kind of project would take. The computer found 20 triads in a little over 3 minutes – it did over 18,700 simple two-number averages to find those. Admittedly the time taken would decrease as elements dropped out of the pool, but this tells us it would take around 112,000 calculations to build a table of Döbereiner triads purely on trial and error. If you were going at a calculation every four seconds (a generous estimate), that’s over 120 hours solid of maths. And that’s if all of the elements even formed triads. Which they don’t. So good luck with that. (The code I made can be found here, if you want to see it.)
The next person to have a crack at a modern Periodic Table was our friend John Newlands, in 1865. He identified that if you line up the elements in order of weight, every 8th element had similar properties. He called this his Law of Octaves, and used it to generate this:
Now this all seemed to be working fine for the first 2 columns- but when we get to the 3rd column, things start to get kooky – and it’s all gone to rot by the fourth column. Lithium and sodium do have similar properties, and rubidium and calcium could be lumped in with them on a foggy night. But silver, copper and osmium are totally different . (This is the second row). The same holds true of the row above – fluorine, chlorine, bromine and iodine are similar, but cobalt, nickel, palladium, platinum and iridium are a whole different kettle of fish.
So we get to the 1870s, and to Russia. Young chemist Dmitri Ivanovich Mendeleev decided to have a crack at this periodic table lark. I say have a crack, he spent 3 days straight without sleep working at it. What he did we pretty revolutionary. He took each of the elements and wrote on a piece of paper along with its atomic weight. These have been called ‘his elemental playing cards’, and allowed him to move whole different patterns around, shuffling rows and columns and patterns seamlessly. For three days and two nights solid he worked, barely stopping to eat and with no sleep at all. And at the end of this long vigil of scientific discovery, he had a eureka moment. A flash of discovery that would change scientific thought for the rest of time.
He decided to have a nap. Not kidding.
And after those 3 long days of working with the elemental playing cards, the shifting patterns hadn’t just filled his waking thoughts. They filled the dream he supposedly had during this nap. And he dreamed the Periodic Table of the Elements.
Here is what he dreamed.
I am entirely aware that this looks nothing like the modern periodic table. It doesn’t. The modern Table looks a bit like a castle, this looks like a box. There are 3 whole classes of elements that haven’t been discovered yet. Only 47% of current elements have been discovered. But this table contains a stroke of pure, unadulterated genius that set this design apart from every other.
There are blanks. Spaces where elements should go. Spaces that modern chemistry would fill over the next 150-odd years. And Mendeleev didn’t try to cover up these spaces, or to pretend they were there to make the numbers crunch. He advertised them. He claimed that his table could be used to predict the atomic weights, properties, even colours of elements so far unknown to mankind. He made three of these predictions – ekasilicon, ekaaluminium and ekaboron – elements whose properties he described. It was a challenge to chemistry to try to prove him wrong.
Over the next 15 years, 3 new elements were discovered. Germanium, gallium and scandium. Aka, ekasilicon, ekaalumiuim and ekaboron. Mendeleev totally called them – he was right about most of their properties. The global science community took this as the proof for the utter and complete correctness of the Periodic Table of Elements.
All that had to be done was to discover the next 62 elements. Next time, on
Serial The Everything Map.