Question

What is periodicity?

Answer 1

Mendeleev arranged the chemical elements according to the recurring properties to form a periodic table of elements. According to Mendeleev, the properties of elements are the periodic function of their atomic masses. This method was rejected because it was not able to explain the position of certain elements and isotopes. The new periodic table was introduced by Moseley known as the modern periodic table according to which, the properties of elements are the periodic function of their atomic number.

Complete answer:
In reference to the periodic table, the periodicity refers to these recurring variations or trends in the properties of elements with increasing atomic number. It is caused by a regular and predictable variation in the atomic structure of elements.
Some of the properties which display periodicity are as follows:
1. Ionization energy: It is the minimum energy required to remove an electron from the valence shell of a gaseous ion. It increases across a period and decreases on moving down the group.
2. Electronegativity: It is the measure of tendency of an atom to attract electrons in order to form a chemical bond. It increases across a period and decreases on moving down the group.
3. Atomic radius: It is equal to half the distance between the centres of the two atoms which are touching each other. It increases on moving left to right across a period and decreases on moving down the group.
4. Electron Affinity: It is the tendency of an atom to accept electrons. It increases across a period and decreases on moving down the group.

Note:
Remember that the noble gases are always considered as exceptions in the periodicity trends of periods due to their inert nature. However, the elements of the noble gas family display periodic properties within the group.