(a) What was Mendeleev's basis for classification of elements?

(b) Mendeleev's contributions to the concept of a periodic table laid the foundation for the Modern Periodic Table. Give reasons.

(a) Mendeleev classified elements according to Mendeleev's Periodic Law. Mendeleev's Periodic Law states that physical and chemical properties of elements are a periodic function of their atomic masses.

(b) As many features of the Mendeleev's periodic table were later used when Modern Periodic Table was made so we can say that Mendeleev's contributions to the concept of a periodic table laid the foundation for the Modern Periodic Table. For example:

1. Mendeleev's periodic table contains vertical column called groups and horizontal rows called periods.
2. They were all in eight groups.
3. All elements in a group had similar properties and same valency.
4. In a period elements gradually changed from metallic to non-metallic character.
5. Mendeleev left some gaps in his periodic table for subsequent inclusion of elements not known at that time.
6. He predicted the properties of then unknown elements on the basis of the properties of elements lying adjacent to the vacant slots.
7. He was able to correct the atomic mass of elements like gold and platinum by placing these elements strictly on the basis of similarities in their properties.