Dmitri Mendeleev: the periodic table
The periodic table is a monument to science, used by scientists around the world, that helps to identify, classify and understand the chemical elements. This famous invention of the Russian chemist Dmitri Mendeleev is called “periodic table of elements” because elements with the same properties recur periodically. Hence the term “periodic” table. But the table was not just periodic, if not predictive.
Let’s take a closer look at the story of this chemist who revolutionised the world of chemistry 150 years ago.
The story of Dmitri Mendeleev
Dmitri Ivanovich Mendeleev was born in Verkhnie Aremzyani, a small village in southern Siberia, on 8 February 1834. Dmitri grew up in a very large family with 17 children. Ivan Pavlovich Mendeleev, the father, is a teacher at a local school, and Maria Dmitrievna, the mother, comes from a family of glass merchants. She spent much of her childhood surrounded by books of all kinds. With a father who was a primary school teacher and a mother who loved books, education was at the heart of this modest family. Shortly after Dmitri was born, his father lost his sight as a result of cataracts. He had to resign from the school where he worked. The meagre government pension did not allow the Mendeleev family to live adequately, so the mother of the family had to take over the family business.
Dmitri loved accompanying his mother to her glassmaking business. He marvelled at the way the sand could melt and turn into translucent, multicoloured glass. His mother encouraged him to always know more and to be curious about everything. He entered the Tobolsk school at the age of 7, where he took a particular interest in science and mathematics.
In 1847, the Mendeleev family suffered another tragedy when the father died of an illness. A year later, in 1848, Maria’s business caught fire. Everything was totally destroyed. With two more children to look after, Maria realised that Dmitri had a great love of science and wanted to enrol him at Moscow University, one of the most prestigious in the country. When the family arrived in Moscow after a four-week journey, Maria saw Dmitri’s enrolment refused by the university on the grounds that he had not studied at a recognised school. Another week’s journey and, that time, Dmitri was able to enrol at the University of St Petersburg.
Probably exhausted by the tragedies she had suffered and all her travels, Maria contracted tuberculosis and died in 1850. Dmitri’s sister, who had accompanied them on the journey, also died of tuberculosis a few months after her mother. Dmitri also contracted tuberculosis but, contrary to the doctor’s dire predictions, he survived.
Although Dmitri was not spared much throughout his childhood, he nevertheless managed to obtain his school-leaving certificate in 1857.
Between 1860 and 1870, Dmitri left his mark on science in St Petersburg. In 1861, he won the Demidov prize for his work on the capillarity of liquids. In 1864, he became a professor at two of the city’s universities and was awarded a doctorate in science in 1865 for his thesis on the combinations of water and alcohol.
Dmitri Mendeleev’s influence was such that by the early 1970s, St Petersburg had become a major centre for chemical research. And it was that place, in just ten years, that Dmitri created his masterpiece: the famous periodic table of elements.
The beginnings of the periodic table
In Antiquity and the Middle Ages, philosophers and alchemists discovered around fifteen elements.
Then, in 1789, it was Antoine and Marie-Anne Lavoisier proposed their elementary treatise on chemistry. This book, considered the bible of chemistry, lists all the following substances – carbon, sulphur, iron, copper, silver, tin, gold, mercury, lead, zinc, arsenic, antimony and bismuth – and adds a few others, such as oxygen, nitrogen, hydrogen and phosphorus. These “simple substances”, as they were called by Lavoisier, were divided into two categories: metals and non-metals. And then Dalton arrived. John Dalton was an English chemist who studied atoms. His research led him to propose in his atomic theory that the lightest element, hydrogen, has a mass number of 1. And the mass number of all the other elements will be measured against this mass. For example, if carbon weighs 12 times the mass of hydrogen, it will have a mass of 12. Scientists therefore had fun calculating the mass of each of the known elements, and a mass classification began to emerge.
In the early 1830s, the chemist Johann Wolfgang Dobereiner realised that certain elements with the same properties could be linked together in groups of three, which he called triads. In the years that followed, scientists tried out some rather original new rankings. Until William Odling, President of the Chemical Society, vetoed the idea and ordered the elements to be classified alphabetically.
Dmitri Mendeleev’s periodic table
It was in this context that Mendeleev made his appearance. By the time he looks into it, a number of things are already known:
- 63 elements are known, along with some of their properties
- The mass of the hydrogen is set to 1, and all the others are measured in relation to the hydrogen
On the basis of these two data, Mendeleev began by classifying the elements in order of mass. First hydrogen, then lithium, beryllium, etc. It then grouped together elements with the same properties. Then he realised that classifying them in rows would not be enough. He then decided to reorganise his classification, putting them in order of mass in the columns and order of properties in the rows. He then realised that everything was rather well organised. But he didn’t stop there, Mendeleev decided to leave gaps in his ranking, and for good reason.
These holes were intended to be filled with elements that did not yet exist. Thanks to his table, he was able to give the approximate mass and properties. He was able to predict elements that were still unknown. Between zinc and arsenic, for example, he didn’t know the names of the elements, but he was able to predict the mass of the two missing elements and their properties. Gallium was discovered six years after his table, and germanium two years later. The two elements fitted perfectly into his table.
He then continued to develop his periodic table and, in 1871, the periodic table took the form we know today. The elements are listed in order of mass in the rows, and grouped by similar properties in the columns.
Despite a very difficult start in life, orphaned at the age of 16, Dmitri Mendeleev imposed his verve and genius to the whole world with his periodic table. This monument to science led to the discovery of a huge number of elements, giving us a better understanding of the composition of the world.