Write a short note on:
Position of isotpes in the Mendeleev's and the Modern periodic table

Explanation

i. Isotopes were discovered long time after Mendeleev developed the periodic table.
ii. All isotopes of the same element have different atomic masses but same atomic number. They also have the same chemical properties.
iii. In Mendeleev's periodic table, elements are arranged in increasing order of their atomic masses such that chemically similar elements are placed together in a group. So, it was difficult to place them in Mendeleev's periodic table.
iv. In modern periodic table, elements are arranged in increasing order of their atomic numbers. Hence, all the isotopes of an element occupy the same position in the modern periodic table.