Modern Periodic Law

Modern Periodic Law

  • The physical and chemical properties of elements are the periodic function of their atomic numbers.

Period number-

  • Periods are the horizontal rows of elements in a periodic table. 
  • There are seven periods in the periodic table. 
  • The period number is related to the number of electron occupied shells in the element.
  • For example, If an element having electronic configuration 2,5.This shows that the number of electron occupied shells in the element is 2. Hence this element belongs to 2nd period.

Number of Elements in a Period

Period Number

Number of Elements

1

2

2

8

3

8

4

18

5

18

6

32

7

32(incomplete)

 Group number-

  • There are 18 vertical columns in the periodic table. Each column is called a group.
  • All elements in a group have similar chemical and physical properties because they have the same number of outer electrons.
  • If the element is in s block, then the group number is equal to the number of valence electrons. 
  • If the element is in the p block, then the number of the group can be determined by the formula:- (number of valence electrons + 10).