Dmitry Mendeleyev, a master’s degree holder in chemistry was a teacher. He won an award to go to Germany to pursue chemical research where he attended a conference. This conference played a key role in Mendeleev’s eventual development of the periodic table. He watched as the conference produced an agreed, standardized method for determining atomic weights of elements. On his return to Russia, he realized that improved Russian language chemistry textbooks were a necessity. In just 61 days the 27 year old chemist poured out his knowledge in a 500 page textbook: Organic Chemistry. This book won the Domidov Prize and put Mendeleev at the forefront of Russian chemical education.
Chemistry was a patchwork of observations and discoveries then. In order to streamline, Mendeleev wrote the names of the 65 known elements on cards – much like playing cards – one element on each card. He then wrote the fundamental properties of every element on its own card, including atomic weight. He saw that atomic weight was important in some way – the behavior of the elements seemed to repeat as their atomic weights increased – but he could not see the pattern. Mendeleev moved the cards about for hour after hour until finally he fell asleep at his desk. When he awoke, he found that his subconscious mind had done his work for him! He knew the pattern the elements followed.
Mendeleyev found that, when all the known chemical elements were arranged in order of increasing atomic weight, the resulting table displayed a recurring pattern, or periodicity, of properties within groups of elements. Mendeleyev discovered the periodic law. His newly formulated law was announced before the Russian Chemical Society in March 1869 with the statement “elements arranged according to the value of their atomic weights present a clear periodicity of properties.” In his version of the periodic table of 1871 of known 70 elements, he left gaps in places where he believed unknown elements would find their place. He even predicted the likely properties of three of the potential elements. The subsequent proof of many of his predictions within his lifetime brought fame to Mendeleyev as the founder of the periodic law.