What did Dmitri Mendeleev do in his periodic table?

Publish his first book in 1869: - Arranged elements in terms of increasing atomic weight - took into account the properties of the elements and their compounds - left gaps for undiscovered elements - showed elements with similar chemical properties lined up in groups - swapped positions of some elements (eg, iodine & tellurium) due to similar chemical properties, despite their weight being in the wrong order