What is a periodic property? How the following properties vary in a group and in a period? Expain
(a) Atomic radius.

Explanation

Periodic property : The repetition of similar physical and chemical properties of elements at regular intervals with increasing atomic number is called periodic property or periodicity.
(a) I.E. (or) I.P. : As we go from left to right in a period atomic radius gradually decreases. As a result of which the nuclear attractions on the valence electrons gradually increases. So, the energy required to remove the outer electrons gradually increases. In other words, as we go from left to right in a period, the I.P. values increase.
As we go from top to bottom in a group, atomic radius gradually increases. As a result of which the nuclear attraction on the valence electrons gradually decreases. So, the energy required to remove the outer electrons gradually decreases. In other words, in a group the I.P. values gradually decrease from top to bottom.
(b) Metallic property : Metallic nature is the tendency to lose electron and form positive ion. T
`M rarr m^(n+) + n e^(-)`
If an element has low electronegativity, then it will have metallic nature.
Metallic nature increases down the group since E.N. decreases. Metallic nature increases across a period as E.N of elements increases.
(c) Atomic radius : In a period, as we go from left to right, the atomic radius gradually decreases.
Reason : As we go from left to right in a period, the differentating electron enters into the same orbit but at the same time, the nuclear charge increases. As a result of which the effective nuclear charge over the outermost electrons increases, leading to a decrease in the the atomic radius.
As we go grom top to bottom in a group, the atomic radius gradually increases.
Reason : As we go from top to bottom in a group, the valence electrons enter into new shells, even though the nuclear charge increases. As a result of which, the effective nuclear charge over the outermost electrons decreases, leading to n increase in the atomic radius.