Describe the differences between groups in the current day periodic table of elements
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The key difference between Mendeleev and modern periodic table is that Mendeleev’s periodic table was based on the increasing atomic masses while the modern periodic table is based on the increasing atomic numbers. Let us see here what is Mendeleev periodic table and what is modern periodic table, and then compare both to understand the difference between both periodic tables. Mendeleev is the pioneer of the modern periodic table, though a numerous number of changes had been made to the old version of the periodic table. Both of these attempts are equally important to the scientific community; because without an invention of the periodic relationship in elements, the modern developments in Science would not reach a development era as today. Before the invention of Mendeleev’s classification, there were several attempts made by several chemists, but their periodic laws were inadequate to apply for all the elements. The modern periodic table is so advantageous for the development in the Science.

The third choice .. (:

And a) oxygen i believe