PERIODIC CLASSIFICATION
MODERN PERIODIC LAW
   In 1913, an English physicist MOSELEY, as a result of his work on characteristics of X-rays of elements    discovered a fundamental and most accurate relation between chemical properties and atomic number    of elements, known as "Modern periodic law".
   ACCORDING TO THE MODERN PERIODIC LAW:

   1. The chemical and physical properties of elements are the periodic function of their atomic    numbers".

   2. The properties of elements depends upon their electronic configuration which vary with    increasing atomic number in a periodic way".
   The modern periodic law provides a logical and scientific ground for the classification of elements.
LONG FORM OF PERIODIC TABLE
   Periods
   Periodic table is divided into seven horizontal rows of elements. Each row of elements is called    "PERIODS".All the elements of a period are different from each other. Period no of an element    indicates number of orbits in the atom of that elements.
   General features of a period
   1- Period number of an element represents number of energy levels in the element. For example,
ELEMENTS
PERIOD
NUMBER OF ENERGY LEVELS
Na (Z=23)
K (Z=39)
Rb( Z=55)
Third
Forth
Fifth
3 (K , L , M)
4 (K , L , M , N)
5 (K , L , M , N , O)
   2- Atomic size decreases in a period.
   3- Nuclear charge increases in a period.
   4- Ionization potential increases in a period.
   5- Electronegativity increases in period.
   6- Electro positivity and metallic character decreases in period.
   7- Each period starts with Alkali metal and ends on a Noble gas.
   For example:
   2nd period : Li .................................. Ne
   3rd period : Na ..................................Ar
   7-First element of each period is most reactive (electropositive), and last element is chemically inert.
   DESCRIPTION OF PERIODS

First period

   It is the shortest period and it contains only two elements (H and He). This period corresponds to filling    up of K-shell. Electronic configuration of the elements of this period is 1S1 and 1S2
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Second period

   It is called first short period and it contains eight elements. This period corresponds to filling up of L-    shell. In this period electrons occupy 2s and 2p orbital. This period contain 2 element of S-block and    six p-block

Third period

   It also contains eight elements and is known as second short period. It corresponds to filling up of M-    shell. It contains 2 S-block and 6 P-block elements. In this period 3S and 3P orbital are being filled.
Fourth period

   It contains 18 elements and is known as first long period. This period corresponds to the filling up of N-    shell. It contains 2 S-block, 6 P-block and 10 d-block (transition) elements. It start with filling 4S    orbital followed by 3d and 4p orbital.

Fifth period

   Fifth period contain 18 elements and is known as 2nd long period. It corresponds to filling up of O-shell.    It starts with the filling of 5S-orbital followed by 4d and 5p orbital.
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Sixth period
   Sixth period contains 32 elements and it is the longest period.
   Among 32 elements
   2 elements of s-block with electronic configuration 6s1 and 6s
   26 elements of p-block with electronic configuration 6s2, 6p1 to 6s2, 6p6 elements 10 of d-block with    electronic configuration 6s2, 5d1 to 6s2, 5d10
   14 elements of f-block with electronic configuration 6s2, 5d1, 4f1 to 6s2, 5d1, 4f14
    In sixth period electrons starts filling 4f-orbital after 5d-orbital accommodate one electron.
Seventh period
   7th period is incomplete period.
   It includes:
   2 elements of s-block with electronic configuration 7s1, 7s2
   10 elements of d-block with electronic configuration 7s2, 6d1 to 7s2, 6d10
   14 elements of f-block with electronic configuration 7s2, 6d1, 5f1 to 7s2, 6d1, 5f14

Groups

   Modern periodic table is divided into eight vertical columns of elements. Each vertical column of    elements is called a "GROUP". The groups of the periodic table are further divided into two sub-groups    or families "A and B". Elements of sub-group "A" are known as Normal elements or Representative    elements. While the elements of sub-group "B" are known as Transition elements. Group number of an    element is represented by roman numerals such as IA, IIA, VIA etc. Group number of an element    indicates its highest oxidation state. Atomic size increases down the group. I.P decreases down the    group.

   General features of a group are as under

   1-Group number of an element shows number of electrons in the outermost shell of that element
ELEMENT
NUMBER OF VALENCE ELECTRONS
GROUP
Na
Cl
C
1
7
4
I-A
VII-A
Iv-A


   2. ATOMIC SIZE: Atomic size of element increases from top to bottom in a group.

   3. NUMBER OF SHELL: from top to bottom number of shell increases by one for each element.

   4. NUMBER OF VALENCE ELECTRONS: No of valence electron are constant.

   5. IONIZATION POTENTIAL: I.P decreases from top to bottom.

   6. ELECTRONEGATIVITY: Electronegativity decreases from top to bottom.

   7. METALLIC CHARACTER : Metallic character increases down the groups
APPLICATIONS OF PERIODIC TABLE

   Arrangement of elements in the form of periodic table is very useful for the proper study of elements.    Some important applications of periodic table are as follows:

  1. Classification of elements into periods and groups is very useful and easy in the study of chemistry.
  2. Suggestions for further research become available.
  3. Prediction of new element is possible.
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