Achivement and limitatioo of mendeleev periodic table
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Achievements are :
Systematic study of elements: As the elements having same properties are grouped together so it becomes very useful to remember the properties of large number of elements in a systematic way.
Prediction of new elements: Mendeleev predicted the properties of those missing elements from the known properties of the other elements in the same group. On the basis of this, he named Gallium as Eka-Almunium, Germanium as Eka-Silicon and Scandium as Eka-Boron.
Correction of atomic mass: Atomic mass of beryllium was corrected from 13.5 to 9. Atomic mass of indium, gold and platinum were also corrected.
Limitations are :
He positioned hydrogen in the first column above alkali metals. He did so because hydrogen and alkali metals have similar properties. However, hydrogen also resembles halogens in many ways. Like halogens, hydrogen is a gas, and exists as a diatomic molecule (H2). Therefore, Mendeleev was not able to explain the position of hydrogen.
Position of isotopes : On the basis of atomic weight , various isotopes of the same elements should be assigned different places in the periodic table. Mendeleev could not provide separate places for isotopes.
Dissimilar elements placed together : Noble metals like Cu, Ag and Au are placed along with chemically dissimilar alkali metals in Group I . Similarly, Mn possessing very few similarities with halogens have been placed in VII group.
Similar elements separated : In Mendeleev's periodic table, certain chemically similar elements such as copper and mercury ; gold and platinum have been placed in different groups.
Systematic study of elements: As the elements having same properties are grouped together so it becomes very useful to remember the properties of large number of elements in a systematic way.
Prediction of new elements: Mendeleev predicted the properties of those missing elements from the known properties of the other elements in the same group. On the basis of this, he named Gallium as Eka-Almunium, Germanium as Eka-Silicon and Scandium as Eka-Boron.
Correction of atomic mass: Atomic mass of beryllium was corrected from 13.5 to 9. Atomic mass of indium, gold and platinum were also corrected.
Limitations are :
He positioned hydrogen in the first column above alkali metals. He did so because hydrogen and alkali metals have similar properties. However, hydrogen also resembles halogens in many ways. Like halogens, hydrogen is a gas, and exists as a diatomic molecule (H2). Therefore, Mendeleev was not able to explain the position of hydrogen.
Position of isotopes : On the basis of atomic weight , various isotopes of the same elements should be assigned different places in the periodic table. Mendeleev could not provide separate places for isotopes.
Dissimilar elements placed together : Noble metals like Cu, Ag and Au are placed along with chemically dissimilar alkali metals in Group I . Similarly, Mn possessing very few similarities with halogens have been placed in VII group.
Similar elements separated : In Mendeleev's periodic table, certain chemically similar elements such as copper and mercury ; gold and platinum have been placed in different groups.
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