Mendeleev's periodic table

Early attempts to classify elements

Before discovering protons, neutrons and electrons, scientists tried to classify the elements by arranging them in order of their atomic weights. The atomic weight of an element is equivalent to what we now call its relative atomic mass.

Early periodic tables were incomplete, since many elements were unknown. Also, some elements were placed in groups with elements that were not similar to them.

Dmitri Mendeleev

Dmitri Mendeleev was a Russian chemist. He wrote chemistry books and was looking for ways to organise the known elements. He published his first periodic table of the elements in 1869. In it, he arranged the elements in order of increasing atomic weights. He…