The factors responsible for the ionization enthalpy of the main group elements to decrease down a group are listed below: (i) Increase in the atomic size of elements: As we move down a group, the number of shells increases. As a result, the atomic size also increases gradually on moving down a group. As the distance of the valence electrons from the nucleus increases, the electrons are not held very strongly. Thus, they can be removed easily. Hence, on moving down a group, ionization energy decreases.
(ii) Increase in the shielding effect: The number of inner shells of electrons increases on moving down a group. Therefore, the shielding of the valence electrons from the nucleus by the inner core electrons increases down a group. As a result, the valence electrons are not held very tightly by the nucleus. Hence, the energy required to remove a valence electron decreases down a group.
Was this answer helpful?
0
0
Top Questions on Electronic Configurations Of Elements And The Periodic Table
Classification of Elements & Periodicity in Properties
Since many elements were being discovered in the 19th century and the study of these elements individually was proving difficult, classification of elements was made necessary.
Classification by Johann Dobereiner - German chemist Johann Dobereiner classified certain elements on the basis of their similar properties in the groups of continuing - three elements each. These groups were called ‘triads’. In every triad, the atomic weight of the middle element was equal to the average of the atomic weights of the first and third elements.
Newlands Law of Octaves - The elements were arranged in increasing order of their atomic weights and found that every 8th element shows similarity with the 1st element.
Mendeleev’s Periodic Table - The arrangement of all 63 elements in rows or columns in order of their atomic weight was made by Mendeleev. He left some space for corresponding elements in his periodic table which were not even discovered till then. Although he predicted the properties of those elements through his periodic classification of elements.
Modern Periodic Law - The properties of the elements of the modern periodic law are periodic functions of their atomic numbers.
