1) Depending upon which sub-shell the differentiating electron enters, the elements are classified into s, p, d and f-block elements. They are 

1. s – block elements, 

2. p – block elements,

3. d – block elements, 

4. f – block elements.

2) s – block elements : 

i) If the differentiating electron enters in s-subshell, then the elements are called s-block elements. 

ii) IA (1), IIA (2) group elements belong to this block. 

3) p – block elements : 

i) If the differentiating electron enters in p-subshell, then the elements are called p-block elements. 

ii) IIIA(13), IV A (14), V A (15), VIA (16), VIIA (17) belong to p-block. 

4) d – block elements : 

i) If the differentiating electron enters in d-subshell, then the elements are called d – block elements. 

ii) I B, II B, III B, IV B, V B, VI B, VII B, VIII B belong to d-block elements. 

iii) They are also called transition elements. 

5) f – block elements : 

i) If the differentiating electrons enter in f-subshell, then the elements are called f-block elements. 

ii) These are divided into two types a) Lanthanides (41 elements), b) Actinides (5f elements). 

iii) These are also called as inner transition elements. 

Advantage of this classification : 

1) The systematic grouping of elements into groups made the study simple. 

2) Each period begins with the electron entering a new shell and ends with the complete filling of s and p-sub-shells of that shell.