State the differences between Modern Periodic Table and Mendeleev's Periodic table.

modern period table

 Modern periodic law states that the properties of elements are a periodic function of 

their atomic numbers, not their atomic masses.

 The modern periodic table consists of 7 periods and 18 groups. Elements having the 

same valence shell are present in the same period. Elements having the same number of 

valence electrons are present in the same group. Metals are present on the right-hand 

side of the periodic table, whereas non-metals are present on the left-hand side of the 

periodic table.

 Group 1, 2 and 13-18: Representative elements

 Group 3-12: Transition elements

 Period 6: Elements with atomic numbers 58-71: Lanthanoids

 Period 7: Elements with atomic numbers 90-103: Actinoids

 The valencies of the elements remain same down the group. However while moving 

across the period, the valency first increases and then decreases.

 The atomic size as well as metallic character of elements increases on moving down the 

group and decreases on moving from left to right in a period.

mandleev's period table

 Mendeleev gave a periodic law which states that the properties of elements are a 

periodic function of their atomic masses. 

 Achievements of Mendeleev’s periodic table:

 Mendeleev left some gaps in his periodic table so that the undiscovered elements 

could get a place in it without disturbing the positions of the other elements.

 Noble metals were not discovered at that time. When they were discovered later, 

they got a place in Mendeleev’s table without disturbing the positions of the other 

elements.

 Mendeleev predicted the existence of gallium and named it as eka-aluminium.

 Limitations of Mendeleev’s periodic table 

 It failed to explain the position of hydrogen. It was not able to explain the position of isotopes.

 In the table some elements having higher mass were kept before the elements having 

lesser atomic mass.