Long Form Of The Periodic Table Or Moseley’s Periodic Table

CBSE Class 12 Chemistry Notes

Elements of second period are called bridge elements.

Characteristic of Groups:

  • Moseley’s periodic table contains sixteen groups. These are represented by Roman numerals I, II, III, IV, V, VI, VII, VIII and zero. Groups I to VII are divided into two subgroups A and B, Group VIII consists of three sets, each one containing three elements.
  • Inert gases are present in zero group.
  • The valency of an element in a group is equal to the group number.
  • There is no resemblance in the elements of subgroups A and B of same group, except valency
  • The elements of the groups which resemble with typical elements are called normal elements. For example IA, IIA, IIIA, IVA, VA, VIA, VIIA group elements are normal elements or main group elements or representative elements.
  • Those elements of the groups which do not resemble with typical elements are called transition elements. For example- IB, IIB, IIIB, IVB, VB, VIB, VIIB, and VIII group elements are transition elements.

Illustration 1. There are 2, 8 and 8 elements in first, second and third periodic of periods table respectively. Explain

Solution: In first period 1s is completed. Its capacity is of two electrons. In second period 2s 2p and in third period 3s 3p are completed. The capacity of these shells is of 8 electrons each. Thus, 2, 8 and 8 elements are present in first, second and third periods respectively.

Causes of Periodicity and Nomenclature


According to the Modern Periodic Law, the Properties of the elements are repeated after certain regular intervals when these elements are arranged in order of their increasing atomic number. Therefore the cause of periodicity in properties is the repetition of similar outer electronic configuration at certain regular intervals.

All the elements of group IA i.e. alkali metals have similar outer electronic configuration i.e. ns1, which are given below

CBSE Class 12 Chemistry Notes
CBSE Class 12 Chemistry Notes

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