Question

Write down three major difference between Mendeleev periodic table and modern periodic table

Answer 1

mendelleve orders on atomic weight
modern is based on atomic number

Answer 2

Mendeleev's periodic table                               Modern periodic tableMendeleev's periodic table is based on atomic mass

Modern periodic table is based on atomic numberMendaleev's periodic table contains about 66 elements.
 Modern periodic table contains about 112 elementsIn Mendeleev's  periodic table there were gaps for undiscovered elements.

Modern periodic table maintains uniformity.In Mendeleev's periodic table noble gases were not placed (as they are not discovered at that time).In Modern periodic table noble gases in a separate group named as group-18.In Mendeleev's periodic table transition elements included with other elements In Modern periodic table transition elements  placed in separate block.