CLASSIFICATION OF ELEMENTS.

1. Define periodic table and write it's founder.
- A chart in which elements are arranged systematically on the basis of their similarity and dissimilarity in periods and groups is called periodic table.

2. Define  periods and group.
- The horizontal rows of a periodic table are called periods. They are seven in number.
- The vertical columns of a periodic table are called groups. Thy ar eighteen in number.

3. State Mendeleev's Periodic law.
- Mendeleev's Periodic law states that, the physical and chemical properties of elements are the periodic functions of their atomic mass.

4. What are the defects of mendeleevs periodic table?
- The defects of mendeleevs periodic table are:
- Hydrogen was placed in group IA along with alkali metals, but it could also be placed along with along with halogens in group VIIA.
- Position of isotopes of same elements was different.
- Alkali metals and coinage metals like copper, gold, silver were put in the same group.
-  There was no proper position of lanthanides and actinides.

5. State modern periodic law.
- It states that, the physical and the chemical properties of elements are the periodic function of the atomic number.