Elements in the long form of periodic table have been divided into four blocks i.e. s ,p ,d and f. This division is based upon the name of the orbitals which receives the last electron.
S block elements
1) Elements in which the last electron enters the s orbital of their respective outermost shells are called s block elements.
2) s sub shell has only 1 orbital which can accommodate only 2 electrons, therefore, there are only two groups of s block elements.
3) Elements of and group 1(hydrogen and alkali metals) and group 2 (alkaline earth metals) and helium comprises s block element.
4) Hydrogen has only one electron and this enters 1s orbital. The rest of the elements i.e. Li, Na, K, Rb, Cs and Fr receive the last electron in 2s, 3s, 4s, 5s,6s and 7s orbitals.
5) Helium and the elements of group 2 i.e. Be, Mg, Ca, Sr, Ba and Ra. The last electron in these elements also enter the s orbital i.e. 1s, 2s, 3s, 4s, 5s, 6s and 7s orbital. These elements also belong to s block and have ns2 as their general outer electronic configuration.
6) There are 14 s-block elements in the periodic table.
General electronic configuration of s-block elements: ns1-2 where n=2-7
Helium belongs to s – block but its positioning with in the p block along with other group 18 elements is justified because it has a completely filled valence shell and thus exhibits properties characteristic of other noble gases.
Because of its unique behaviour, we shall place hydrogen separately at the top of the periodic table it because:
1) It has a single s-electron and hence can be placed along with alkali metal group.
2) It can also gain one electron to acquire a noble gas configuration and hence can be placed along with halogens.
Characteristics of s-block elements
1)They are soft metals with low melting and boiling points.
2)They have low ionisation enthalpies and are highly electropositive.
3)They lose the valence electrons readily to form +1 and +2 ions.
4)They are very reactive metals . The metallic character and reactivity increases as we move down the group. Because of high reactivity, they are never found pure in nature.
5)The compounds of s-block elements with the exception of beryllium are predominantly ionic.
6)Most of the metal of this blog impart characteristic colour to flame.
7)They are strong reducing agents.
8)All are good conductors of heat and electricity.
P block elements
Elements in which the last electrons enter any one of the three p orbitals of their respective outermost shell are called p block elements.
1) A p sub shell has three degenerate p orbitals ,each one of which can accommodate 2 electrons.
2) There are 6 groups of p block elements. These are 13,14,15,16, 17and 18.
3) The atoms of the elements belonging to these groups receive the last electron in 2p, 3p, 4p, 5p and 6p orbitals.
4) Their outer shell electronic configuration vary from ns1 np6 to ns2 np6 as we move from group 13 outward up to group 18.
5) Elements of group 13, 14 ,15 ,16 ,17 ,18 in which p orbitals are being progressively filled in are called p block elements. There are 36 p-block elements in the periodic table.
6) Group 18 are called noble gases, except helium all the elements have closed shell ns2 np6 electronic configuration in the outermost shell. All the energy levels which are occupied are completely filled and this stable arrangement of electrons cannot be easily altered by addition or removal of electrons. As a result , these elements are highly stable and hence exhibit very low chemical reactivity.
7) The elements of group 17 are called halogens while those of group 16 are called chalcogens. Elements have high negative electron gain enthalpy and hence readily add one or two electrons to attain the stable noble gas configuration.
The elements of s and p block are called representative or main group elements.
Characteristics of p block elements
1) P block elements include both metals and non-metals but the number of non metals is much higher than that of metals. Metallic character increases from top to bottom within a group and non metallic character increases from left to right along a period.
2) Their ionisation enthalpies are relatively higher as compared to those of s block elements.
3) They mostly form covalent compounds.
4) Some of them show more than 1 Oxidation state in their compounds.
5) Their oxidising character increases from left to right in a period and reducing character increases from top to bottom in a group.
Elements in which the last electron enters any one of the five d orbitals of their respective penultimate shells are called d- block element.
Since a d sub shell has 5 d-orbitals, each one of which can accommodate 2 electrons ,therefore, in all there are 10 vertical columns comprising 10 groups of d- block elements namely 3, 4 ,5 ,6 ,7 ,8 ,9 ,10 ,11 and 12.
The atoms of the elements belonging to these groups usually have 1 or 2 electrons in the s orbital of the outermost shell i.e. ns orbital while the electrons are being progressively filled in, one at a time in the d orbital of the respective penultimate shell i.e. (n-1) d orbital.Thus
General outer shell electronic configuration of d block elements: (n-1)d1-10 ns1-2
The properties of these elements are midway between those of s- block and p- block elements ,they are also called transition elements .All these elements are further divided into four series called 1st ,2nd ,3rd and 4th transition series.
The first transition series forms a part of the fourth period of the long form of periodic table.It contains 10 elements from scandium(Z=21) to zinc( Z=30) in which 3d orbitals are being progressively filled in.
The second transition series which forms a part of the 5th period also contains 10 elements from Ytterium(Z= 39) to cadmium(Z=48) in which the 4d orbitals are being progressively filled in.
The third transition series which form a part of the sixth period also contains 10 elements i.e. lanthanum(Z=57) and from hafnium(Z=72) to mercury(Z=80) in which the 5d orbitals are the progressively filled in.
The fourth transition series which forms a part of 7th period also contains 10 elements i.e. actinium (Z=89) and element from rutherfordium(Z=104) to Copernicium( Z=112) .In all these elements 6d orbitals are being successively filled in.
The elements of group 3 ,4 ,5 ,6 ,7 ,8 ,9 ,10 ,11 and 12 belonging to 4th 5th 6th and 7th period in which the last electron enters the d orbital of their respective penultimate shells are called d Block Elements. There are 40 d block elements in the periodic table.
General characteristics of d-block elements
1)They are hard ,malleable and ductile metals with high melting and boiling point.
2)They are good conductors of heat and electricity.
3)Their ionisation enthalpy are between s and p block elements.
4)They show variable oxidation States.
5)They form both ionic and covalent compounds.
6)Their compounds are generally coloured and paramagnetic.
7)Most of the transition metals such V, Cr, Mn, Fe, Co, Ni, Cu etc and their compounds are used as catalyst.
8)Most of the transition metals form alloys.
9)Zn, Cd and Hg which have the (n-1) d10 ns2 electronic configuration, do not show most of the properties of transition elements.
The elements in which the last electron enters any one of the 7 f-orbitals of their respective ante -penultimate shell are called f block elements.
In all these element the s orbital of last shell is completely filled ,the d orbital of the penultimate(n-1) shell invariably contains 0 or one electron but the f orbital of the ante-penultimate (n-2) gets progressively filled in.
General outer shell electronic configuration of f block elements: (n-2) f 0-14 (n-1) d0-1 ns2
There are two series of f block elements each containing 14 elements. These are placed at the bottom of the periodic table.
The elements of the first series i.e. cerium(Z=58) to lutetium(Z=71) which form a part of the sixth period are called as lanthanides or lanthanoids since all these elements follow lanthanum in the periodic table and also closely resemble lanthanum in their properties. These are also called rare Earth elements since they occur scarcely in the earth crust. In lanthanides ,4f orbitals are been progressively filled in.
The elements of the second series i.e. thorium( Z=90) to lawrencium(Z=103) which forms are part of the incomplete 7th period are called actinides are actinoids since all these elements follow actinium in the periodic table and also closely resemble actinium in their properties. 5f orbitals are being progressively filled in.
The first 3 elements i.e. Thorium, protoactinium and uranium occur in nature but the remaining 11 elements i.e. neptunium(Z=93) to lawrencium(Z=103) have been prepared artificial through nuclear reactions.
All the f block elements i.e. lanthanides and actinides are also called inner transition elements since they form transition series within the transition elements of d- Block.
Characteristics of f block elements
1)They are heavy metals
2)They have high melting and boiling point
3)The show variable Oxidation State
4)Their compounds are generally coloured
5)They have high tendency to form complexes
6)Most of the elements of the actinide series are Radioactive.