From the earliest times, scientists have been trying to classify the available elements on the basis of their properties.
Dobereiner proposed the law of triads'. Newland proposed the law of octaves. Mendeleeff divides the elements into groups on the basis of "atomic weights". The limitations in Mendeleev's periodic table are removed in the modern periodic table.
In modern periodic table eighteen groups and seven periods. There are 's' block, `p' block, `d' block and 'f' block elements.
Atomic radius, Ionization energy, electron affinity, Electro negativity are the main characteristic of the enlacements both in groups and periods