PERIODIC PROPERTIES

 INTRODUCTION:-

To describe periodic properties many scientists give different type of hypothesis .Like:-

  1. Prout's  hypothesis
  2. Doberenier's  Triads
  3. The telluric Helix
  4. Newland's rule of octave 
  5. Lother mayers volume curves
  6. Mandeleef's Periodic Table.
  7. Modern periodic table.


At present time we use Mandeleef  periodic table and modern periodic table  to understand the periodic properties:-

According to the Mandeleef periodic table:-

  • Periodic table is based on atomic weight.
  • Horizontal lines are called PERIODS.
  • Vertical lines are called  GROUPS.
  • The periodic table is consists of SEVEN PERIODS and NINE GROUPS.
  • The earlier periodic table had only 8 groups:the noble gases were added later in the zero group because these were not discovered when Mandeleef  put forward his periodic table.
  • All these groups (except VIII and zero groups are divided into subgroups A and B.
  • 2,8,18 and 32 are called magic numbers.

Merits of Mandeleef's  periodic table:-

  1. Classification of elements then known was done for the first time and the elements having similar properties were kept in the same group.
  2. It encouraged research and let to discovery of newer elements.

DEFECTS OF MANDELEEF'S PERIODIC TABLE:-

  1. POSITION OF HYDROGEN:- Hydrogen resembles alkali metals and halogens in its properties. Hence  its position was not sure.


      2.POSITION OF ISOTOPES:- Have different atomic weights and the periodic table is based on atomic weights. Therefore , isotopes should get different places in the periodic table on the basis of atomic weights.



        3. The periodic table is not fully based on increasing order of atomic weights.


      4.It is not proper place together the elements having different properties, such as COINAGE METALS(Cu,Hg and Au) with alkali metals;Zn,Cd and Hg with alkaline earth metals and metal like Mn with HALOGENS.

Similarly Pt and Au having similar properties have been placed in different groups.


       5.POSITION OF ISOBARS:-These elements have different groups when mass remains same.


MODERN PERIODIC TABLE AND IT'S LAW:-

  • According   to this "the properties of elements are the periodic functions of their atomic numbers".
  •  The nuclear charge on an atom is equals to the atmic number.

MODERN PERIODIC TABLE:-

Scientist Bohr proposed a long form of periodic table that was prepared by Rang and warner.

*Horizontal lines = periods 
*Vertical lines = Groups.

Number of periods =  seven,
Number of Groups = 18.

According to CAS system  the number  of groups is 16 because 8th group has been divided into three groups.

  •       Ist period = 2 elements,
  •       2nd  and 3rd period = 8 elements,
  •        4th and 5th = 18 elements,
  •         6th period = 32 elements,
  •         7th period = 19 elements.
7th period is incomplete period.

The lanthanides (elements from 58 to 71) and actinides (elements from atomic numbers 90 tp 103) are included in the 6th and 7th periods though these have been kept outside the periodic table.


THANKS FOR READING.

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