The periodic system in chemistry – still going strong at 150 years

Chemists still use the table that groups elements according to their properties most days in their work.

The periodic system for elements will turn 150 this year. In 1869, the Russian chemist Dmitri Mendeleev put the smallest parts of the universe in order, as he grouped the 63 elements known at the time into a table.

- The significance of the system for the field of chemistry was revolutionary at that time. The world found its order. The existence of elements was understood. It was understood that there is a certain number of them, and that they have different properties, says Markku Leskelä, Professor Emeritus in chemistry at the University of Helsinki.

As he ordered them, Mendeleev left spaces among the elements in his table. Based on the properties of the elements, he deduced that new elements would be discovered to fill the spaces.

And they were. As years passed, the number of elements rose to 118. The latest were added to the table a couple of years ago.

- The system still isn’t complete. More elements are sure to be discovered, says Professor Timo Repo from the Department of Chemistry at the University of Helsinki.

The table will not be complemented from nature, but rather, scientists are searching for elements with the help of accelerators in lab conditions.

The road is long from the discovery of a new element to it becoming a part of the periodic table. All in all, it may take up to ten years.

Gad­olin’s dis­cov­ery

Finnish scientists have also been part of the mapping of the periodic system. Johan Gadolin, who worked as chemistry professor at the Academy of Turku and the University of Helsinki at the turn of the century 1700-1800, managed to extract a hitherto unknown compound of rare earth metals from a stone that came from Ytterby in Sweden.

It was only later that analyses revealed that the compound contained several rare earth metals, one of which was named gadolinium after Gadolin in due course.

Gadolin himself did not understand that he’d discovered a chemical element, but spoke of a ‘rare type of soil,’ Leskelä says.

Today, as a rare earth metal, gadolinium is a sought-after raw material in the electronics industry. It is used in smartphones, among other things.

According to Repo, who studies catalysts, i.e. materials that accelerate chemical reactions, the periodic system is still an important tool for the chemists of today.

I myself use the system nearly every day, says Timo Repo.

- I myself use the system nearly every day. I can check which elements have similar properties as another, for example, he explains.


The anniversary of the system is celebrated around the world. Unesco has declared this year to be the International Year of the Periodic Table.

The website of the International Union of Pure and Applied Chemistry (IUPAC) lists the celebrations in different parts of the world. The website also contains a quiz on the periodic table.

You can follow the theme year on social media under the hashtag IYPT2019.

The Finnish Chemical Society will organise its own celebration of the system on 7 February at the Science Corner in the University of Helsinki. Facebook Event:

 Kaikki maailman aineet- Jaksollinen järjestelmä-ilta 7.2.2019

Updated 5.2.2019