The physical and chemical characteristics of elements are a periodic function of their atomic masses, in accordance with Mendeleev’s Periodic Law. Mendeleev organised the elements in ascending order of their atomic masses after classifying them according to their atomic masses.
The physical and chemical properties of elements are periodic functions of their atomic weights.
Features of Mendeleev’s Periodic Table
● Twelve horizontal rows, which were condensed to 7, known as periods.
● Eight vertical columns known as groups.
● Groups I to VII subdivided into A and B subgroups.
● Group VIII doesn’t have any subgroups and contains three elements in each row.
● Elements in the same group exhibit similar properties.
Achievements of Mendeleev’s Periodic Table
1. A systematic study of elements: Elements with similar properties were grouped together, that made the study of their chemical and physical properties easier.
2. Correction of atomic masses: Placement of elements in Mendeleev’s periodic table helped in correcting the atomic masses of certain elements. For example, the atomic mass of beryllium was corrected from 13.5 to 9. Similarly, atomic masses of indium, gold, platinum etc., were also corrected.
3. Prediction of properties of yet to be discovered elements: Eka-boron, eka-aluminium and eka-silicon were the names given to yet to be discovered elements. The properties of these elements could be predicted accurately from the elements that belonged to the same group. These elements, when discovered were named scandium, gallium, and germanium, respectively.
4. Placement of noble gases: When discovered, they were placed easily in a new group called zero group of Mendeleev’s table, without disturbing the existing order.
Limitations of Mendeleev’s Periodic Table
1. Position of hydrogen: Hydrogen resembles both, the alkali metals (IA) and the halogens (VIIA) in properties, so, Mendeleev could not justify its position.
2. Position of isotopes: Atomic weight of isotopes differ, but, they were not placed in different positions in Mendeleev’s periodic table.
3. Anomalous pairs of elements: Cobalt (Co) has higher atomic weights but was placed before Nickel (Ni) in the periodic table.
4. Placement of like elements in different groups: Platinum (Pt) and Gold (Au) have similar properties but were placed in different groups.
5. Cause of periodicity: He could not explain the cause of periodicity among the elements.
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