Periodic law: the discovery of a masterpiece

The enduring significance of the periodic table of chemical elements 150 years after it was first published

The periodic table, as significant today as it was when first published 150 years ago. Getty Images

It was on March 6, 1869, that Russian scientist Dmitri Mendeleev published the first periodic table. It was an ad hoc chart, titled "draft of system of elements: based on their atomic masses and chemical characteristics".

It was controversial, because it validated the belief that atoms existed and it identified a fundamental scientific truth that other scientists had not previously been able to express: the periodic law. A law that demonstrated there are connections between chemical elements.

Mendeleev grouped them together as per similar properties and atomic weights. Through this, he was even able to predict the existence of other elements that had not yet been discovered. To get them all to properly align, however, he needed to leave blank spaces – and three of those were filled in during his lifetime with newly noted elements (gallium, scandium and germanium). "Before the promulgation of this law the chemical elements were mere fragmentary, incidental facts in nature," he said.

Now, 150 years on, March 6 arguably remains the most important date on the chemistry calendar, which is why the anniversary is being marked as the International Year of the Periodic Table. "The periodic table of chemical elements is one of the most significant achievements in science, capturing the essence not only of chemistry, but also of physics and biology," the official website for the campaign states.

Activities and celebrations are taking place across the Middle East. In Lebanon, on April 17, the ChemCarnival is being organised at the American University of Beirut. In Iraq, a day later, a festival is taking place at the University of Baghdad to allow secondary school students to discover the hidden potential of chemistry.

Rumour has it, Mendeleev put it all together in a single day, on March 1. He had, of course, been thinking about it for years, as other chemists at the time, as well as in the preceding decades, were also considering the idea of relationships between the elements. How deeply Mendeleev truly understood the intricacies of what he'd done was debatable, but he and scientists across the world then – and now – continue to realise its impact.

As the chemist Peter Atkins once wrote: “The periodic table is arguably the most important concept in chemistry.”