With a better understanding of the part that the electron plays great role in the properties of the elements, a corresponding understanding of the periodic system came about.
On the basis of electronic configuration, the elements may be divided into four groups.
(i) s-Block elements
(a) These are present in the left part of the periodic table.
(b) These are IA and IIA i.e. 1 and 2 group elements.
(c) These are metals.
(d) In these elements last electron fills in the s-orbital.
(e) Electronic configuration of valence shell is ns1−2 ( n = 1 to 7).
(ii) p − block elements
(a) These are present in right part of the periodic table.
(b) These constitute the groups IIIA to VIIA and zero groups i.e. groups 13 to 18 of the periodic table.
(c) Most of these elements are metalloids and non metals but some of them are metals also.
(d) The last electron fills in p-orbital of valence shell.
(e) The electronic configuration of valence shell is ns2np1−6 ( n = 2 to 7).
(f) ns2np6 is stable noble gas configuration. The electronic configuration of He 1s2.
(iii) d−Block elements
(a) These are present in the middle part of the periodic table (between s & p block elements.
(b) These constitute IIIB to VIIB, VIII, IB and IIB i.e, 3 to 12 groups of the periodic table.
(c) All are metals.
(d) The last electrons fill in ( n − 1)d orbital.
(e) The outermost electronic configuration is (n-1)d1-10 ns1−2 (n = 4 to 7).
(f) There are three series of d-block elements as under:
3d series − Sc(21) to Zn (30)
4d series − Y (39) to Cd (48)
5d series − La (57), Hf (72) to Hg (80)
(iv) f−Block elements
(a) These are placed separately below the main periodic table.
(b) These are mainly related to IIIB i.e. group 3 of the periodic table.
(c) There are two series of f−block elements as under:
4f series − Lanthanides − 14 Elements from Ce (58) to Lu (71)
5f series − Actinides − 14 Elements from Th (90) to Lw (103)
(d) The last electron fills in ( n − 2) f-orbital
(e) Their outermost electronic configuration is (n−2)f1−14 (n−1)s2 (n−1)p6 (n−1)d0−1ns2 ( n = 6 and 7).