Dmitri Mendeleev

Mendeleev’s great achievement: Arranging all of the 63 elements into groups possessing similar properties. The 63 elements at that time were identified by their atomic weights. Mendeleev’s first sketch of a periodic table of the elements

Details of how Mendeleev designed the first Periodic Table of Elements He wrote down information on each element on cards. He noticed that the atomic weight (we now refer to as the atomic mass) could be used to rank the elements from lightest to heaviest.

Mendeleev noticed that if you looked at their chemical properties there was a periodicity of properties, (patterns at regular intervals or similarity between properties) especially if you left spaces where the properties did not fit. He stressed that there was order to the elements, and that this order would help predict elements not yet discovered. Details of how Mendeleev designed the first Periodic Table of Elements

Mendeleev’s table as published in 1869, with many gaps and uncertainties

Mendeleev predicted the properties of aluminum, boron, and silicon. Gallium, scandium, and germanium were also found to fit his predictions. There were some discrepancies, but the format of the table is the basis of today’s periodic table. Mendeleev’s table as published in Details of how Mendeleev designed the first Periodic Table of Elements