It’s 150 years since Mendeleev created the periodic table of elements, but what actually goes into organising the building blocks of the universe?

Mendeleev’s work into constructing the modern periodic table is one of the most vital pieces of work in chemistry. The periodic table of elements compiles all the known chemical elements in a concise format. This format allows chemists to quickly look at the chemical and physical properties of the elements and even predict the characteristics of undiscovered elements. But Mendeleev wasn’t the only one working on this puzzle.

Who would’ve guessed that the origins of the periodic table of chemical elements lay with the (attempted) creation of a Philosopher’s Stone in 1669? In this pursuit, German amateur alchemist, Hennig Brand discovered ‘cold fire’, a glowing white substance produced when heating residues of boiled urine. This was the first scientific discovery of a chemical element. We now know this element to be phosphorus. This discovery was later supported in a publication by British chemist Robert Boyle in 1680.

Antoine Lavoisier made the first attempt to classify the known chemical elements in 1789. In this classification, elements were grouped simply by their basic properties: ‘gases’, ‘non-metals’, ‘metals’, and ‘earths’. In 1829 the German chemist Johann Wolfgang Döbereiner’s studies led him to formulate a system of ‘triads’ – four groups of three ‘chemically analogous’ elements arranged in increasing order of their atomic weights. 

Thirty-three years later, Alexandre Béguyer de Chancoutois, a French geologist, came up with a three-dimensional arrangement. The elements were plotted in order of atomic weight around a cylinder – one complete turn corresponded to an atomic weight increase of 16. In this model, elements with similar properties appeared in a vertical line. This model was the first periodic arrangement of all the known elements at the time.

British chemist John Newlands had noticed similarities in elements with atomic weights that differed by seven. He proposed this ‘Law of Octaves’ in 1865. His arrangement of the periodic table did not leave any gaps for undiscovered elements (notably, the noble gases). He sometimes squeezed two elements into one box of the table to maintain his desired patterns. Unsurprisingly, the Chemical Society refused to publish his work.

Julius Lothar Meyer was another German chemist who worked on developing the periodic table between 1864 and 1870. He arranged elements in columns by their increasing valency (the combining power of an element to other atoms). 

Mendeleev published his periodic table in 1869. Mendeleev’s periodic table was the basis for the one we see plastered over classrooms and coffee mugs around the world today. Meyer’s arrangement was very similar to Mendeleev’s, but he did not publish his work until 1870 – a year too late. Mendeleev incorporated the most significant findings of previous scientists’ work to produce a table which arranged the elements by their increasing atomic weights whilst allowing some flexibility to ensure the elements were still correctly grouped by their properties. He even left spaces in the table in anticipation of the discoveries of new elements.

Since then, the periodic table has had some revisions. When William Ramsay discovered the noble gases during the 1890s, they were soon added to the table as group 0. The final piece of the puzzle was added in 1913 when Henry Moseley determined why there were exceptions to ordering the elements by atomic weight. Moseley studied atomic structures and realised that Mendeleev had inadvertently put the elements in order of increasing proton number, rather than atomic mass.

It may not seem so, but the importance of the periodic table within chemistry is huge. Anyone who’s ever done any chemistry in the last 150 years will have used it. Without this seemingly simple tool, knowing the complex characteristics of each chemical element, and the relationships between them would be so much more difficult. Thank you, Dmitri Mendeleev!

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