10th Class Science Periodic Classification of Elements Dobereiners Classification

Dobereiners Classification

Category : 10th Class

*       Dobereiner’s Classification

 

In the year 1829, Johann Wolfgang Dobereiner, a German scientist, was the first to classify elements into groups based on John Dalton's assertions. He grouped the elements with similar chemical properties into clusters of three, called 'Triads'. The distinctive feature of a triad was the atomic mass of the middle element. When elements were arranged in order of their increasing atomic mass, the atomic mass of the middle element was approximately the arithmetic mean of the other two elements of the triad.

 

Elements Atomic mass Average Atomic Mass
Lithium 7  
Berellium 9 9
Potassium 11  

               

Elements Atomic mass Average Atomic Mass
Carbon 12  
Nitrogen 14 14
 Oxygen 16  

               

Elements Atomic mass Average Atomic Mass
Calcium 40  
Strontium 87.5 88.1
Barium 11  

 

Elements Atomic mass Average Atomic Mass
Chlorine 35  
Bromine 80 80.6
Iodine 127  

 

*           Drawback of Triad Classification

  • A large number of similar elements could not be grouped into triads e.g., iron, manganese, nickel, cobalt, zinc and copper are similar elements but could not be placed in the triads.
  • It was possible that quite dissimilar elements could be grouped into triads.
  • Dobereiner could only classify 3 triads successfully. Since he failed to arrange the then known elements in the form of triads his attempt at classification was not very successful.

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