How could the modern periodic table remove various anomalies of Mendeleev’s Periodic Table?

AcademicChemistryNCERTClass 10

As the modern periodic law is based on the atomic numbers of elements, all the anomalies of Mendeleev\'s periodic table were removed. For example:
  1. The position of isotopes could be explained, which Mendeleev\'s periodic table failed to explain. As all the isotopes of an element have the same atomic number, so they could be placed under the same group in a periodic table. For example, Cl-35 and Cl-36, the isotopes of Chlorine with the same atomic number 17, can be placed in the same group of the periodic table.
  2.  Mendeleev could not explain why cobalt was placed before nickel. This problem was solved by the modern periodic law as the atomic numbers of cobalt and nickel are 27 and 28, respectively. Therefore, cobalt with a lower atomic number was placed before nickel in the modern periodic table.
  3. The hydrogen element has been placed at the top of group 1, above the alkali metals because the electronic configuration of hydrogen is similar to those of alkali metals. Both, hydrogen as well as alkali metals have 1 valence electron each.
Updated on 10-Oct-2022 13:19:15