Mendeleev's Periodic Table

According to Mendeleev's periodic law:

All the chemical properties of elements are periodic function of their atomic masses.

(a) The achievements of Mendeleev's periodic table were:

• Mendeleev kept some blank spaces in the periodic table for the elements that were yet to be discovered.

Predicted element

Actual element discovered later

Eka-boron                              Scandium

Eka-aluminium                       Gallium

Eka-silicon                             Germanium

• He also predicted properties of some elements even before their discovery and were later found to be correct.

Property                               Eka-aluminium                   Gallium

Atomic mass                        68                                       69.7

Formula of oxide                  E2O3                                 Ga2O3

Formula of chloride              ECl3                                  GaCl3

• Mendeleev’s periodic table could accommodate noble gases when they were discovered.

(b) Mendeleev took the formulae of the oxides and hydrides formed by the elements as the basic properties of elements for their classification in the  periodic table.

• He was unable to locate hydrogen in the periodic table.
• Increase in atomic mass was not regular while moving from one element to another. Hence, the number of elements yet to be discovered was not predictable.
• Later on, isotopes of elements were found which violated Mendeleev’s periodic law.