Periodic Table and Periodic Classification

Periodic Table and Periodic Classification

Notes-

History of Periodic Table-

1. Lavoisier's Classification
     Lavoisier's divided them known element into two group metal and non-metal.
     His classification was rejected after discovery of metalloids

2. Dobereiner's  Triads-
    Triad- Group of three

Li⁷          Na²³           K³⁹
     (7+39)/2=23

He classified or arrange the element in a group of three such that the atomic mass of middle element is the approximate average of the atomic masses of the two terminal.

Ca⁴⁰          Sr⁸⁸            Ba¹³⁷
          (40+137)/2= 177/2 =88.5

* He could arrange  limited element in the form of triad.

3. Newland's Law of Octave-

According  to Newland if element are arrange in increasing order of their atomic mass than every 8th element has properties similar to first element.

* He could arrange element up to Ca only

4. Lother-Meyer's Classification-  

* A curve was plotted between atomic volume and atomic weight.
* Element with similar properties on the curve.

Alkali metal --Peak Positions.
Halogen --Ascending part
Alkaline earth metal --Descending part   

Drawback-
* Practically is not possible to remembered the position of element on the graph.      

5. Mendeleev's Periodic law and Periodic Table-