The elements in the long from of the periodic table can be divided into four main blocks i.e., s,p,d and f blocks respectively.
1). s-block elements :
The elements in which the last electron enters the s-orbital of their outermost energy level are called s-block elements. This block constitute elements of groups 1 and 2 having the general outer shell electronic configuration as ns1 and ns2 respectively. The elements corresponding to ns1 configurations are called alkali metals while those corresponding to ns2 configurations are called alkaline metals.Thus, the general electronic configuration of s-block elements may be expressed as ns1or2.
General characteristics of s-block elements:
With the exception of hydrogen,the general characteristics of s-block elements are:
(1) They are soft metals having low melting and boiling points.
(2) They are highly reactive and reactive and readily from univalent or bivalent positive ions by losing the valence electron.
(3) They have low ionisation energies.
(4) They are strong reducing agents.
(5) They show oxidation state of +1 and +2 respectively.
(6) They generally form ionic compounds.
(7) They are good conductors of heat and electricity.
(8) Most of them impart characteristic colours to the flame. For example,sodium salts impart a golden yellow colour to the flame.
2). p-block elements:
The elements in which the last electron enters the p-orbital of their outermost energy level are called p-block elements.This block constitutes elements of group 13,14,15,16,17, and 18 having the general outer shell electronic configurations as ns2 np1or-6 (except helium which has the electronic configuration 1s2).
The elements belonging to the eight groups of the s and p block are also called normal or representative elements.
General characteristics of p-block elements:
The general characteristics of p-block elements are:
(1) They include both metals and non-metals but the number of non-metals is much higher than that of metals.There is a regular gradation from metallic to non-metallic character as we move from left to right.
(2) They form mostly covalent compounds except halogens.
(3) Their oxides may be basic (in case of metals),amphoteric (in case of metalloids) and acidic (in case of non-metals).
(4) Their ionisation energies are relatively high as compared to s-block elements.
(5) They are reducing agents and oxidising agents as well. Flourine is the strongest oxidising agent.
(6) Their electronegativity is high.
3).d-block elements:
The elements in which the last electron enters the d-orbitals of their last but one (penultimate,second last)energy level are called d-block elements or transition elements.This block constitutes elements of groups 3,4,5,6,7,8,9,10,11 and 12 having the general outer shell electronic configuration as (n-1) d1or-10 ns o or -2.
The d-block elements are further divided into four series called first,second, third and fourth transition series.The first three series are complete while the fourth is incomplete.
First transition series: The first three series contains 10 elements from scandium (z=21) to zinc (z=30).
Second transition series: This series contains 10 elements from yttrium (z=39) to cadmium (z=48).
Third transition series:This series also contains 10 elements from lanthanum (z=57),hafnium (z=72) to mercury (z=80).
Fourth transition series:This series contains only 6 elements and is incomplete.
General characteristics of d-block elements:
The general characteristics of d-block elements are:
(1) They are hard metals having high melting and boiling points.
(2) They from ionic as well as covalent compounds.
(3) They show variable oxidation states.
(4) Most of them form coloured compounds.
(5) Most of the transition elements are used as catalysts.
(6) They form alloys,interstitial compounds and non-stoichiometric compounds.
4).f-block elements:
The elements in which the last electron enters the f-orbitals of the ante- penultimate (third to the outermost shell) are called f-block elements.This block constitutes two series (14 elements in each series) known as lanthanides and actinides. Their general outer,shell electronic configuration is (n-2) f 1or-14 (n-1)d 0-or1 ns2 where n=6 for lanthanides and n=7 for actinides. The f-block elements are also called inner transsition elements or rare earth elements.
General characteristics of f-block elements:
The General characteristics of f-block elements are :
(1) They are heavy metals.
(2) They show variable oxidation states.
(3) They from complexes.
(4) They have high densities.
(5) They from coloured ions.
(6) Actinides are radioactive in nature.