CLASSIFICATION OF THE ELEMENTS :
It is based on the type of orbitals which receives the differentiating electron (i.e., last electron).
When shells upto (n - 1) are completely filled and the last electron enters the s-orbital of the outermost (nth) shell, the elements of this class are called s-block elements.
Group 1 & 2 elements constitute the s-block.
General electronic configuration is [inert gas] ns1-2
s-block elements lie on the extreme left of the periodic table.
This block includes metals.
Group - IA or 1 Alkali metals :
Group - II A or 2 , Alkaline earth metals :
When shells upto (n -1) are completely filled and differentiating electron enters the p-orbital of the nth orbit, elements of this class are called p-block elements.
Group - III A or 13 , boron family :
Group - IV A or 14 , carbon family :
Group - V A or 15 , nitrogen family :
Group - VI A or 16 , Oxygen family :
When outermost (nth) and penultimate shells (n - 1)th shells are incompletely filled and differentiating electon enters the (n -1) d orbitals (i.e., d-orbital of penultimate shell) then elements of this class are called d-block elements.
3d 21Sc -30Zn 3d
4d 39Y - 48 Cd 4d
5d 57La, 72 Hf-80Hg 5d
6d 89Ac, 104Rf - 112Uub 6d (incomplete series)
Those elements which have partially filled d-orbits in neutral state or in any stable oxidation state are called s transition elements.
When n, (n-1) and (n -2) shells are incompletely filled and last electron enters into f-orbital of antepenultimate i.e., (n-2)th shell, elements of this class are called f-block elements., General electronic configuration is (n - 2)f1-14 (n - 1)d0-1 ns2
All f-block elements belong to 3rd group.
They are metals
Within each series, the properties of the elements are quite similar.
They are also called as inner-transition elements as they contain three outer most shell incomplete and were also referred to as rare earth elements since their oxides were rare in earlier days.
The elements of f-block have been classified into two series:
The actinides and lanthanides have been placed at the bottom of the periodic table to avoid the undue expansion of the periodic table.
1. Ist inner transition or 4 f-series, contains 14 elements 58Ce to 70Lu. Filling of electrons takes place in 4f subshell.
2. IInd inner transition or 5 f-series, contains 14 elements 90Th to 103Lr. Filling of electrons takes placed in 5f subshell.
PREDICTION OF PERIOD, GROUP AND BLOCK:
(a) For s-block elements Group number = the no. of valence electrons.
(b) For p-block elements Group number = 10+ no. of valence electrons .
(c) For d-block elements Group number = no. of electrons in (n - 1) d sub shell + no. of electrons in valence shell.