Classification of elements into blocks
According to the electronic configurations;of elements; four blocks-are envisaged in the periodic table. If the differentiating electron of an element enters s subshell, it is placed in s block. Similarly the other three p, d and f blocks are also indicated in the periodic table. The positions of the blocks asre shown in the figure 2.3
When the elements are arranged according to their electronic configurations, n^t only four blocks are formed but also the elements having similar electronic configurations in their outer shells appear in the same vertical column termed as group. The elements of the same group have similar chemical properties.
The elements having one electron in s orbital of their outer shells (ns ') are called group I elements (hydrogen, alkali metals). The elements with two electrons in s orbital (ns2) of their outer shells are called group II elements (alkaline earth metals). The elements with three electrons (two in 's ' and one in p orbitals (ns2 np 1) in their outer shells are called group III elements. In a similar way, the elements having four, five, six, seven and eight electrons in their outer shells belong to groups IV, V, VI, VII, and O respectively.
s block : s orbital can have a maximum of two electrons, in it. Therefore s block has two groups in it. They are
Group I : (H, Alkali metals ) Electronic configuration of outer shell ns1
GroupII: (Alkaline earth metals) Electronic configuration of outer shell ns2 The electronic configuration of s block elements is ns1 or ns2
p block : It has six groups as the three p orbitals together can accomadate a maximum of six electrons. The groups are.
Group III: (Boron family ) Electronic configuration of outer shell ns2 np1
Group IV : (Carbon family ) Electronic configuration of outer shell ns2 np2
Group V : (Nitrogen family) Electronic, configuration of outer shell ns2 np3 .
Group VI: (Oxygen family ) Electronic configuration of outer shell ns2 np4
Group VII: (Halogens ) Electronic configuration of outer shell ns2 np5
Group O : (Noble Gases) Electronic configuration of outer shell ns2 np6 except He which has 1s2 configuration.
The electronic configuration of p block elements varies from ns2 np1 to ns2 np6
d block :The block has ten groups as the five d orbitals can accommodate, totally a maximum of ten electrons. The differentiating electron enters the penultimate or (n-l) shell of atoms of the elements. The general configuration of d block elements is (n - 1) d1-10 ns1-2 where i.e. n= 4, 5 , 6 or 7. As 3d, 4d and 5d orbitals are filled with electrons, three series each with ten elements are formed. The fourth series that comes due to electrons entering into 6d orbitals is incomplete.
3d series : From scandium (Z = 21) to zinc (Z = 30), in the fourth period.
4d series : From yttrium (Z = 39) to cadmium (Z = 48) in the fifth period.
5d series : After the element lanthanum (Z=57)the differentiating electrons complete 4f orbitals and then enter 5d orbitals from hafnium (Z = 72)to mercury (Z = 80) to form the third series in the sixth period.
6d Series : There is incomplete 6d series from actinium (Z = 89) in the seventh period
f series : The differentiating electron enters f orbitals of antipenultimate or (n -2) shell in atoms. The general outer shells configuration of f block elements is (n -2)f1-14 (n -1 )d0-1, ns2 where n =6 or 7 The block has two series and each series has 14 elements.