When most people think of the chemical elements, they picture Mendeleyev’s Periodic Chart of the Elements. This organizational table has served as the one accepted organizing system for the elements that make up our planet for 125 years.
It is so important that it is taught to every student in beginning chemistry classes. It led to the discovery of new elements and has been a cornerstone of chemists’ understanding of the properties and relationships of Earth’s elements. It has also helped in the design and conduct of chemical experiments and greatly sped the development of science’s understanding of the basic elements in the early twentieth century.
By 1867, 33-year-old Dmitri Mendeleyev had landed a position as chemistry professor at St. Petersburg University, a remarkable accomplishment for the youngest of 14 children of a Russian peasant. With an untamed thicket of hair, a wild, trailing beard, and dark, penetrating eyes, Mendeleyev was called “that wild Russian” by other chemists in Europe. In 1868 he began work on a chemistry textbook for his students.
The question he faced in beginning the book was how to arrange and organize the growing list of 62 known elements so that his students could understand their characteristics. By this time, Mendeleyev had collected a hoard of data from his own work and, mostly, from the work of others, especially from the English chemists Newland and Meyers and Frenchman de Chancourtois.
Mendeleyev sorted the elements by atomic weight; by family resemblance; by the way they did, or did not, combine with hydrogen, carbon, and oxygen; by the kind of salts they formed; by whether an element existed as a gas, liquid, or solid; by whether an element is hard or soft; by whether an element melts at a high or low temperature; and by the shape of the element’s crystals. Nothing allowed him to make sense of all 62 known elements.
Then Mendeleyev, a skilled piano player, realized that the notes on a piano repeated at regular intervals. Every eighth key was a “C.” He realized that in seasons, in waves at the beach, even in trees, characteristics repeat over and over after a set period of time or distance. Why shouldn’t the same thing happen with the elements?
He wrote each element and its various characteristics on cards and spread them across a table, arranging and rearranging the cards, searching for repeating patterns. He quickly found that every eighth element shared many family traits, or characteristics. That is, most of the time, every eighth element shared characteristics with the others in this family. But not always.
Mendeleyev was again stuck. One day that summer, it struck him that it was possible that not all of Earth’s elements had been discovered. His chart of the elements had to allow for missing elements.
He returned to his stack of cards and arranged them into rows and columns so that the way that the elements in each column bonded with other elements was the same, and so that the physical characteristics of the elements in each row were the same.
All of the known elements fit perfectly into this two-dimensional chart. However, he had to leave three holes in the chart that he claimed would be filled by three as-yet-undiscovered elements. Mendeleyev even described what these “missing” elements would look like and act like based on the common traits of other elements in their row and column. All Europe laughed and said his predictions were the crazy ramblings of a wild fortuneteller.
Three years later the first of Mendeleyev’s “missing” elements was discovered in Germany. The scientific community thought it an interesting coincidence. Within eight years the other two had also been found. All three looked and behaved just as Mendeleyev had predicted.
Scientists around the world were amazed and called Mendeleev a genius who had unlocked the mysteries of the world of chemical elements. His discovery has guided chemical research ever since.
Mendeleyev’s periodic chart helped dispel the ancient alchemist’s myth of turning lead into gold. In 1980, American scientist Glenn Seaborg used a powerful cyclotron to remove protons and neutrons from several thousand atoms of lead (atomic number 82), changing it into gold (atomic number 79). No, he didn’t create instant wealth.
The process is so expensive that each atom of gold he created cost as much as several ounces of gold on the open market.