Solution of Defects of Mendeleef Modern periodic Table by long form of Periodic Table
Answers
Defects in Mendeleev Periodic Table
1. Anomalous pairs
The following pairs of elements did not follow Mendeleev’s Principles:
Cobalt (58.9) with higher atomic mass precedes Nickel (58.6) in the periodic table.
Tellurium (127.6) with higher atomic mass than Iodine (126.9) is also placed before it in the periodic table.
2.The position of hydrogen
Hydrogen was not given a fixed position. It was considered in Group IA as well as in Group VIIA, because it forms a positive ion as in HCl but also a negative ion as in NaH.
3. Electronic arrangement
It does not explain the electronic arrangement of elements.
4.Grouping of chemically dissimilar elements
Elements such as Copper and Silver bear no resemblance with the alkali metals such as Lithium and Sodium etc., but they have been placed together in the first group.
5.Position of Isotopes
The isotopes of an element are atoms of that element having similar chemical properties but different atomic masses. According to Mendeleev’s Periodic Law, isotopes of an element must be given separate places in the periodic table because they have different atomic masses.
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(i) Modified the place of elements present in the table of Mendeleif. That is, elements of the same qualities together and unequal properties. Elements were kept separate
Example- longitudinal period consists of 7 spirits and 18 squares.
(ii) Class - 1 or IA and square-2 or IIA (s-block elements) are placed in the left part of the long periodic table. The transit elements have been kept in the middle. Elements of classes 13 to 18 (p-block elements) are placed in the right part of the long periodic table.
(iii) The transition elements are grouped together in the middle of the periodic table in the period of 3 to 12 in the long periodic table, and lanthenoid and actinoid elements are placed in two horizontal rows below the periodic table.
(iv) In this category, isotopes have been given equal and equilibrium space because the atomic numbers of isotopes are equal and atomic numbers of equilibrium are different.