Mendeleev’s Periodic Table

Mendeleev’s Periodic Law:

Physical and chemical properties of elements are the periodic function of their atomic masses.
Mendeleev’s periodic table is based on the chemical properties of elements.
Mendeleev’s periodic table contains vertical columns called ‘groups’ and horizontal rows called ‘periods’.
Achievements of Mendeleev’s Periodic Table: 63 elements were known at the time of classification.

  • Elements with similar properties could be grouped together.
  • Mendeleev left some gaps in his periodic table. Mendeleev boldly predicted the existence of some elements that had not been discovered at that time.
  • Noble gases discovered, could be placed without disturbing the existing order.

Remember
Scandium, gallium and germa-nium have properties similar to Eka-boron, Eka-aluminium and Eka-silicon respectively.

Limitations of Mendeleev’s Classification

  • The position of hydrogen in the table was not certain because it could be placed in the group of alkali metals as well as in halogens.
  • Isotopes of elements were placed in the same position in the table though according to their atomic masses, they should have been placed in different positions.
  • Certain elements of higher atomic mass proceed those with lower atomic mass. For example, tellurium (atomic mass 127.6) precedes iodine (atomic mass 126.9). Iodine was placed after tellurium though it had lower atomic mass because Iodine had properties similar to bromine and not selenium.