Question

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

Answer 1

Periodicity in properties of elements in the modern periodic table means the repetition in the properties of the elements at regular intervals when arranged according to increasing atomic number.
Elements in the same group have similar properties as their electronic configurations have the same number  of electrons in the outermost shell

 Tendency to gain electrons increases on moving from left to right in a period as the effective nuclear  charge increases and the atomic radius decreases.