State 3 points of difference between Mendeleev's periodic table and modern periodic table
Answers
Mendeleev's periodic table Modern periodic table
Mendeleev's periodic table is based on atomic mass
Modern periodic table is based on atomic number
Mendaleev's periodic table contains about 66 elements.
Modern periodic table contains about 112 elements
In 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 seperate 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.
The main differences are:
1) Mendeleev's periodic table is based on atomic mass. Modern periodic table is based on atomic number.
2) Mendaleev's periodic table contains about 66 elements. Modern periodic table contains presently 118 elements.
3) In Mendeleev's periodic table there were gaps for undiscovered elements.Modern periodic table maintains uniformity.
4) 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 seperate group named as group-18.
5) In Mendeleev's periodic table transition elements included with other elements. In Modern periodic table transition elements placed in separate block.
6) According to Mendeleev's, the isotopes with different atomic weights, should be placed in different positions, but are not given any position and no justified reason was explained. In Modern periodic table, the isotopes were assigned same position as they have same atomic number.