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Write the drawbacks in Mendeleev's periodic table that led to its modification.

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Following are the drawbacks in Mendeleev's periodic table: -

  • Hydrogen's position-
    Hydrogen resembled the properties of both alkali metals(like lithium) and also that of halogens(like iodine). Hence, the position of hydrogen(whether hydrogen is to be placed with halogens or alkali metals) was not specified.

  • Position for Isotopes-
    Mendeleev's periodic table was based on arranging elements in increasing order of atomic masses. But isotopes were not included in his periodic table.

  • Certain elements were arranged in reverse order. Elements having higher atomic mass were placed in front(or before) the elements with less atomic mass. Example - Cobalt and Nickel
    Cobalt being more heavier than Nickel ,was placed before Nickel , in the Mendeleev's periodic table.

  • Several gaps were left in the periodic table as he believed that several elements are yet to be discovered. For instance – Gallium was not discovered at that time.
  • Position of VIII Group is inappropriate.
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