Question

What is periodicity?

Answer 1

Hint: As we know that, according to modern periodic tables there are 118 elements till now. The elements are having its own characteristics as size, ionization enthalpy, oxidizing and reducing property etc.

Complete answer:
According to the modern periodic law, the physical and chemical properties of the elements are arranged in a periodic function of their atomic numbers. When the elements are arranged in the order of their increasing atomic numbers, it is observed that the elements of similar properties occur at regular intervals or periodically. Therefore, in the periodic table there are 18 columns called groups and 7 horizontal rows called periods in which the series of elements are arranged in a family whose atoms have the same number of electron shells which is known as principal quantum number n. Each successive period in the periodic table is associated with the filling of the next higher principal energy level (n = 1,n = 2,n = 3,n = 4).
The succession of periods forms the groups with increasing principal energy level. The first two groups in the periodic table is called s-block and from group \[{\rm{1}}{{\rm{3}}^{{\rm{th}}}}\]to \[{\rm{1}}{{\rm{8}}^{{\rm{th}}}}\] is known as p-block.
There are three rows between s-block and p-block called as transition elements and other two different rows are known as Lanthanides and Actinides.

Note: As we move from s-block (left) to p-block (right), the nuclear charge increases and size decreases. Therefore, the most of the elements in p-block are gases.
As we move from top to bottom, the size of elements increases due to increase in the principle energy level.