What is periodicity in properties of elements with reference to the Modern Periodic Table? Why do all the elements of the same group have similar properties? How does the tendency of elements to gain electrons change as we move from left to right in a period? State the reason of this change.
Periodicity means the properties of elements are periodic functions of their atomic number.
Since all the elements of a group have the same number of valence electrons , they have similar chemical properties.
As we move from left to right across a period, the effective nuclear charge increases and the ability to accept electrons also increases.