how does modern periodic law different from mendellevs periodic law? explain any two defects of mandellev periodic table which were o
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Mendeleev’s periodic table is, based on relation of properties of elements as dependent on the atomic weight of element. But Modern periodic table considers atomic number as the fundamental property that decides the properties of elements.
Modern periodic table does correct defects of the Mendeleev’s periodic table. For example, in the Mendeleev’s periodic table, in the element pairs, Argon-potassium, cobalt-nickel, tellurium-iodine and thorium and protactinium, elements with higher atomic mass precedes the element with lower atomic weight. Though it is the right places for them but is against the Mendeleev’s periodic law.
These elements atomic number shows the reverse order compared to atomic mass. The supposed to be wrong positions in Mendeleev’s table has the right explanation justifying their positions.
Uneven grouping of elements:
In Mendeleev’s periodic table, coinage metals of copper, silver, and gold are, grouped together with very active alkali metals. Manganese metal was, grouped with halogens in the seventh group. The defects are rectified in the Modern periodic table.
Position of isotopes:
Isotopes with higher atomic weights could not, be accommodated in the Mendeleev’s table. As isotopes have same atomic number with the stale atom they do not need any separate location in the modern periodic table.
No reasons were, offered for the triad elements of viii group. No such special grouping is given in the modern table.
Mendeleev’s periodic table was for the arrangement of sixty-three elements known at that time.
Modern table accommodates all the 118- natural and synthetic elements.
Atomic number is much fundamental property distinguishing each element and hence a better basic nature to decide the physical and chemical properties of elemental atoms than atomic weights.