Mendeleev’s periodic law and table is the first systematic attempt to classify elements on the fundamental property of the element/atom.
i) Give more weight to similarities in properties than to atomic mass in the arrangement. Iodine, though of smaller weight (127) than Tellurium (128) is placed later as it resembles more to chlorine and bromine than to oxygen and Sulphur. Similarly cobalt and nickel do not follow increasing atomic mass.
ii) Correction of atomic mass:
From the periodic properties, elements of beryllium, indium, gold and platinum were predicted to be having incorrect mass and lead to the re estimation of their real mass.
iii) Prediction of new elements:
Could predict the existence and properties of three elements, of properties similar to boron,
aluminum and silicon. These elements are named Eka-boron, Eka-aluminum and Eka-silicon. They were isolated and named as scandium, gallium and germanium respectively.
Experimentally determined atomic weight, physical properties and their chemical formula for their oxides and halides exactly matched with that predicted by Mendeleev.
The incomplete periods indicated the existence of yet to be discovered elements.
iv) Noble gases were discovered much later. Since they show inert behavior and zero valences, they could be easily attached to the Mendeleev’s table.