write a short note on Mendeleev periodic table
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in mendeleev periodic table of elements there are 114 elements were found. there are 6 periods
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the statement that the chemical and physical properties of the elements recur periodically when the elements are arranged in the order of their atomic weights. There are afew elements still missing, according to the periodic law which has been so valuable in chemistry.
HERE ARE SOME DRAWBACKS OF MENDELEEVS PERIODIC TABLE
Position of hydrogen:- hydrogen resembles both, alkali metals (IA) and the halogens (VIIA) in properties so Mendeleev could not decide where to place it.
2. Position of Isotopes:- As atomic weight of Isotopes differ, they should have been placed in different position in Mendeleev's periodic table. But there was no such places for Isotopes in his table.
3. Cause of periodicity:- Why physical and chemical properties repeated in a group.
4. Anamolous pairs of elements:- There were some pair of elements which did not follow increasing order of atomic weights.
Example: Ar&K, Te&I, Co&Ni, Th&Pa
5. Gaps in his period table:- Mendeleev left several gaps in his periodic table, proposing that some of the elements were still undiscovered
Example: Eka Aluminium - Gallium(Ga), Eka Silicon - Germanium(Ge), Eka Boron - Scandium(Sc), Eka Mangenese - Technetium(Tc).
6. Like elements were placed in different groups.
Example: Platinum (Pt) and Gold(Au) have similar properties but were placed in different groups Pt(VIII) and Au(IB).
7. Unlike elements were placed in same groups.
Example: Cu, Ag and Au were placed in Ist group with Na, K etc while they differ in their properties.
8. It was not clear that lanthanides and Actinides are related with IIIA group or IIIB group.
hope this help u
HERE ARE SOME DRAWBACKS OF MENDELEEVS PERIODIC TABLE
Position of hydrogen:- hydrogen resembles both, alkali metals (IA) and the halogens (VIIA) in properties so Mendeleev could not decide where to place it.
2. Position of Isotopes:- As atomic weight of Isotopes differ, they should have been placed in different position in Mendeleev's periodic table. But there was no such places for Isotopes in his table.
3. Cause of periodicity:- Why physical and chemical properties repeated in a group.
4. Anamolous pairs of elements:- There were some pair of elements which did not follow increasing order of atomic weights.
Example: Ar&K, Te&I, Co&Ni, Th&Pa
5. Gaps in his period table:- Mendeleev left several gaps in his periodic table, proposing that some of the elements were still undiscovered
Example: Eka Aluminium - Gallium(Ga), Eka Silicon - Germanium(Ge), Eka Boron - Scandium(Sc), Eka Mangenese - Technetium(Tc).
6. Like elements were placed in different groups.
Example: Platinum (Pt) and Gold(Au) have similar properties but were placed in different groups Pt(VIII) and Au(IB).
7. Unlike elements were placed in same groups.
Example: Cu, Ag and Au were placed in Ist group with Na, K etc while they differ in their properties.
8. It was not clear that lanthanides and Actinides are related with IIIA group or IIIB group.
hope this help u
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