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Question

Briefly explain the first classification of elements and Mendeleev's periodic table.


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Solution

Dobereiner triads:

  • The first classification of elements was done by Dobereiner
  • He tried to arrange the elements with similar properties into groups. He identified some groups having three elements each. So he called these groups ‘triads'.
  • Dobereiner showed that when the three elements in a triad were written in the order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

Mendeleev's periodic table:

  • Prediction of new elements: The existence and properties of elements that are similar to Boron/Aluminum/Silicon is predicted by Mendeleev.
  • Mendeleev's Periodic Law states that the properties of elements are the periodic function of their relative atomic masses.”
  • He left the gap after some elements and gave them hypothetical names such as Eka-Alumium/Eka-Silicon.
  • He took more similarities in properties than to atomic mass in the arrangement such as Iodine I has a smaller weight than Tellurium Te but it was placed after it.
  • From the periodic properties, Beryllium Be, Indium In, Gold Au, and Platinum Pt were predicted to be having inaccurate mass which lead to the re-estimation of their real masses.

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