Mendeleev’s Periodic Table:

Introduction:

This law was proposed by Russian chemist Dmitri Mendeleev in 1869.

Statement:

According to Mendeleev’s periodic law

The properties of elements are a periodic function of their atomic masses.

Explanation:

Like Newland, he also arranged the known 63 elements in the increasing order of their atomic weights in his periodic table in 8 vertical columns and 6 horizontal rows called groups and periods, respectively.After the discovery of noble gases and radioactive elements another version of Mendeleev’s periodic table was published in 1905. In this version ‘0’ group was added to accommodate the noble gases and the seventh period for the radioactive elements of 1905.

Merits of Mendeleev’s Periodic Table:

Gaps or Vacant/Empty Spaces: Mendeleev left some gaps in his periodic table for some of the unknown elements based on the properties of the other elements present in the same group.
The Naming of the Elements: He named these missing elements as Eka(1) boron, Eka aluminium, and Eka silicon. Later on, these elements were discovered and named scandium, gallium, and germanium, respectively.
Correction of Atomic Masses: Mendeleev corrected the doubtful atomic weights of some elements. For example, the atomic weight of indium, i.e., 76 later he wrote the atomic weight of indium is 113. He also corrected the atomic weights of the elements beryllium and uranium.

Demerits of Mendeleev’s Periodic:

Anomalous Pairs: In Mendeleev’s periodic table, there are some pairs of elements in which the element with a higher atomic weight is placed before that of the lower atomic weight element in order to maintain the similarity in chemical properties of the elements belonging to the same group.

The pairs are (i) Co & Ni (ii) Te &I (iii) Ar & K

Position of Hydrogen: The position of hydrogen is not justified.
Positions of Isotopes: The isotopes of an element have different atomic weights. But there is no position for the isotopes in Mendeleev’s periodic table.
Position of Lanthanides and Actinides: Two sets of 14 elements each (lanthanides and actinides, respectively), which follow lanthanum and actinium in the order of atomic weights, have not been provided regular or separate places in the periodic table. They have just been put together along with lanthanum and actinium respectively.
Position of Elements of Group VIII: Three triads of the transition elements are placed in group VIII of the periodic table. They should have been given separate positions.
Anomalous placement of the transition and coinage metals:

(a) Transition elements were placed along with typical elements under the same group.

(b) Coinage metals were placed with alkali metals.

Owing to these limitations and the later discovery of atomic structure, Mendeleev’s periodic table has no practical significance at present.