DIVISION OF PERIODIC TABLE INTO s-, p-, d- AND f-BLOCKS ON THE BASIS OF ELECTRONIC CONFIGURATIONS
The long form of periodic table can be divided into four main blocks. These are s-, p-, d- and f-blocks. The division of elements into blocks is primarily based upon their electronic configuration as shown in Fig. 6.2.
Fig. 6.2. Division of periodic table into various blocks.
The elements in which the last electron enters the s-sub- shell of their outermost energy level are called s-block elements. This block is situated at extreme left of the periodic table. It contains elements of groups 1 and 2. Their general configuration is ns1-2, where n represents the outermost shell. the elements of group 1 are called alkali metals whereas the elements of group 2 are called alkaline earth· metals. are:
Some of the general characteristics of s-block elements
(i) They are soft metals. Hardness decreases with increasing atomic number.
(ii) They have low melting and boiling points.
(iii) They have low ionization energies and hence are highly electropositive.
(iv) They are very reactive metals.
(v) They show oxidation states of +1 (in case of alkali metals) or +2 (in case of alkaline earth metals).
(vi) They are good reducing agents.
(vii) The compounds of s-block elements are predominantly ionic.
The elements in which the last electron enters the p-subshell of their outermost energy level are called p-block elements. The ·general configuration of their outermost shell is ns2 np1-4i. The only exception is helium (l s2). Strictly, helium belongs to the s-block but its positioning in the p-block along with other group 18 elements is justified because it has completely filled valence shell ( 1 s2) and as a result, exhibits properties characteristic of other noble gases. This block is situated at the extreme right of the periodic table and contains elements of groups 13, 14, 15, 16, 17 and 18 of the periodic table. Most of these elements are non-metals, some are metalloids and a few others are heavy elements which exhibit metallic character. The non-metallic character increases as we move from left to right across a period and metallic character increases as we go down the group. Some of the general characteristics of p-block elements are:
(i) They show variable oxidation states.
(ii) They form ionic as well as covalent compounds.
(iii) They have relatively higher values of ionization energy.
(iv) Most of them are non-metals.
(v) Most of them are highly electronegative.
(vi) Most of them form acidic oxides.
The elements in which the last electron enters the d-subshell of the penultimate energy level are called d-block elements. Their general valence shell configuration is (n -l)d1-10, ns1-2, where n represents the outermost energy level. d-Block contains three complete rows of ten elements in each. The fourth row is incomplete. The three rows are called first, second and third transition series. They involve the filling of 3d, 4d and 5d orbitals respectively. The d-block contains elements of groups 3 to 12 of the periodic table. The general characteristics of d-block elements are:
(i) They are hard, high melting metals.
(ii) They show variable oxidation states.
(iii) They form coloured complexes.
(iv) They form ionic as well as covalent compounds.
(v) Most of them exhibit paramagnetism.
(vi) Most of them possess catalytic properties.
(vii) They form alloys. For example, brass is an alloy of copper and zinc.
(viii) They are good conductors of heat and electricity.
The elements in which the last electron enters the f –sublevel of the anti-penultimate (third to the outermost shell) shell are called f-block elements. Their general configuration is (n – 2)f1-14 (n – 1) d 0-1 , Ns2, where n represents the outermost shell. They consist of two series of elements placed at the bottom of the periodic table. The elements of first series follow lanthanum (57La) and are called lanthanoids. The elements of second series follow actinium (89Ac) and are called actinoids. Actinoid elements are radioactive. Many of them have been made only in nanogram quantities or even less by nuclear reactions. Chemistry of the actinoids is complicated and is not fully studied. The general characteristics of !-block elements are:
(i) They show variable oxidation states.
(ii) They are high melting metals.
(iii) They have high densities.
(iv) They form complexes, most of which are coloured.
( v) Most of the elements of actinoid series are radioactive.