5 drawbacks of Mendeleev periodic table
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some drawbacks are...
(A) Position of hydrogen : Position of hydrogen in the periodic table is uncertain. It has been placed in 1A group with alkali metals, but certain properties of hydrogen resemble those of halogens. So, it may be placed in the group for halogens as well.
(B) Position of isotopes : Isotopes are the atoms of the same element having different atomic masses. Therefore, according to Mendeleev’s classification these should be placed at different places depending upon their atomic masses. For example, hydrogen isotopes with atomic masses 1,2 and 3 should be placed at three places. However, isotopes have not been given separate places in the periodic table because of their similar properties.
(C) Anomalous pairs of elements “ In certain pair of elements, the increasing order of atomic masses was not obeyed. In these, Mendeleev placed elements according to similarities in their properties and not in increasing order of their atomic masses
(A) Position of hydrogen : Position of hydrogen in the periodic table is uncertain. It has been placed in 1A group with alkali metals, but certain properties of hydrogen resemble those of halogens. So, it may be placed in the group for halogens as well.
(B) Position of isotopes : Isotopes are the atoms of the same element having different atomic masses. Therefore, according to Mendeleev’s classification these should be placed at different places depending upon their atomic masses. For example, hydrogen isotopes with atomic masses 1,2 and 3 should be placed at three places. However, isotopes have not been given separate places in the periodic table because of their similar properties.
(C) Anomalous pairs of elements “ In certain pair of elements, the increasing order of atomic masses was not obeyed. In these, Mendeleev placed elements according to similarities in their properties and not in increasing order of their atomic masses
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1. 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:- 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), Scandium(Sc),
2. Position of Isotopes:- 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), Scandium(Sc),
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