Contruction of modern periodic table.

The tabular arrangement following aufbau principle is called long form periodic table.
The periodic table is sub-divided on the basis of electronic configuration. In periodic table the horizontal lines or rows are called periods. There are seven periodic in all explained as:



Period 1 (n = 1):-

There is only one energy level (k-shell) for the elements of this period. It is the shortest period and contains only two elements as Hydrogen and Helium with electronic configuration.



Period 2 (n = 2):-

There are two shells (k, L) for the elements of this period. It contain 8 elements from Lithium to Neon. It is called first short period.



Period 3 (n = 3):-

There are three energy level for the elements of this period ( K, L, M) for the elements of this period. It also contains 8 elements fron Na to Ar. It is called second short period.



Period 4 (n = 4):-

There are four energy levels ( k , L , M, N)

It contain 18 elements from K to Kr. It is called first long period.



Period 5 (n = 5):-

There are five energy levels ( k , L , M, N, O)

It contain 18 elements from Rb to Xe. It is called second long period.



Period 6 (n = 6):-

This period contains 32 elements from cs to Rn. This period include 2 elements of s-block, i.e Cs and Ba , 10 elements of d-block from La to Hg , 14 elements of f-block from ce to Lu , 6 elements of p-block from Tl to Rn.



Period-7 (n = 7):-

This periodic includes 2 elements of s-block Fr and Ra, 10 elements of d-block With configuration and 14 elements of f-block (Actinides series) i.e Th to Lr.

Groups:-

The vertical coloumn in the periodic table are called groups. The elements with similar electronic configuration show similar properties and are placed in one group. There are 8 groups for each family (i.e A&B).There are 18 vertical coloumn.

Periods:-

The repetation of similar chemical properties after certain fixed intervals is known as periodicity. The repetation in properties of elements in due to repetation of similar electronic configuration of outer most energy levels of elements after certain intervals.

Elements of periodic table have been divided into s, p , d and f blocks on the basis of electronic configuration.



A) Noble Gases:-

      In the periodic table, the noble gases are found at the end of each period in zero groups. These are also known as Inert gases of reference group. VIII A group consist on six gases having complete outer shell, therefore they do not react with any atom or molecule at normal comdition. They are colourless and diamagnetic. Except Helium all the noble gases posses octet confuguration.

B) Representative (Typical) Elements or Active Elements or Normal Elements:-

  All the elements of A sub-groups of the periodic table are called representative or typical elements. These including metals, non-metals and metalloids. These include elements of s and p block.

1) s-Block:-
  These are the elements in which last electron enter in the s sub-shell therefore they are known as s-block elements. This block consists of group IA (Li, Na, K, Rb, Cs and fr), also known as Alkali metals and group IIA (Be, Mg, Ca, Sr, Ba and Ra), also known as alkaline earth metals. All the elements of this block are electropositive.

2) p-Block:-
 IIIA to VIIIA group elements are known as p-block elements. These are the elements in which outer most electron enter in the p sub-shell. They have their general configuration. These are the thirty elements in p-block, among these one is liquid (i.e Br) nine are gases, ten are metals (poor) and ten are non-metals.

C) Transition Elements:-

3) d-Block Elements:-

  These are the elements in which outer most electron enter in the d sub-shell, there these elements are known as d-block elements. As they are situated between s block and p block therefore they are known as outer transition elements. IB to VIIIB group elements are known as d-block elements. There are four series of elements 4th is incomplete.

4) f-Block:-
  These are the elements in which extra electron enter in the f-orbital are called f-block elements. As they are situated between IIIB and IVB groups therefore they are also known as inner transition elements. They consist on two series of 14 elements i.e Lanthanides and Actinides series. These block allotted a number IIIB (other than IIIB of d-block).

Dobereiner's Trails Rule:-

  In 1829 J.W Dobereiner discover that if three elements are arranged in ascending order with respect to atomic masses and in such arrangement mass middle element is approximately the arithemtic mean of sum of masses of other two elements then they can show similar chemical properties. These are called Dobereiner's traids.

Newland's Law of Octave:-

An English chemist in 1864-1869 proposed another periodic law for classification of elements as " If elements are arranged in ascending order with respect to their atomic masses then properties of every eight element were similar to those of the first".