Discuss five demerits of Mendeleev's periodic table. How were these limitations overcome in the modern periodic table?
Discuss five demerits of Mendeleev's periodic table. How were these limitations overcome in the modern periodic table?
Step : Five demerits of Mendeleev's periodic table
.Atomic mass:
Mendeleev placed elements in the table based on the atomic mass. But the increase of atomic masses was in a random manner. Some elements with smaller atomic mass were placed after elements with higher atomic mass. For Example, Cobalt (Co) with atomic no. (59.9 ) is placed before the Nickel (Ni) with atomic no (58.6)
.Position of Hydrogen:
There was no fixed position for the Hydrogen because it had an electronic configuration similar to alkali metals and halogens.
.Position of Isotope:
Isotopes are elements with the same atomic number but with different atomic mass. So it wasn't easy to place them as one element occupied two places.
.Properties of elements:
Elements that do not have the same properties were placed in the same groups. For example, Manganese (Mn) was placed in the halogens group, but its properties differed from the halogens.
.Position of Lanthanides:
Lanthanides and Actinides were placed against the periodic law. They were placed in the main body of the periodic table.
Step : Limitations overcome in the Modern Periodic Table:
.Based on the atomic number:
Elements are arranged based on their atomic numbers in the modern periodic table. So there is a fixed position for Hydrogen(H).
2. Isotopes:
There are no places for isotopes as the elements are placed according to the atomic numbers, and isotopes have the same atomic no.
. Lanthanides and Actinides:
Lanthanides and Actinides are kept separately at the bottom of the table. They are placed in the f-block of the periodic table.
.Properties of elements:
Elements with the same properties are placed in the same group. For example, group 17 is of halogens which have similar chemical properties.
Step : Five demerits of Mendeleev's periodic table
.Atomic mass:
Mendeleev placed elements in the table based on the atomic mass. But the increase of atomic masses was in a random manner. Some elements with smaller atomic mass were placed after elements with higher atomic mass. For Example, Cobalt (Co) with atomic no. (59.9 ) is placed before the Nickel (Ni) with atomic no (58.6)
.Position of Hydrogen:
There was no fixed position for the Hydrogen because it had an electronic configuration similar to alkali metals and halogens.
.Position of Isotope:
Isotopes are elements with the same atomic number but with different atomic mass. So it wasn't easy to place them as one element occupied two places.
.Properties of elements:
Elements that do not have the same properties were placed in the same groups. For example, Manganese (Mn) was placed in the halogens group, but its properties differed from the halogens.
.Position of Lanthanides:
Lanthanides and Actinides were placed against the periodic law. They were placed in the main body of the periodic table.
Step : Limitations overcome in the Modern Periodic Table:
.Based on the atomic number:
Elements are arranged based on their atomic numbers in the modern periodic table. So there is a fixed position for Hydrogen(H).
2. Isotopes:
There are no places for isotopes as the elements are placed according to the atomic numbers, and isotopes have the same atomic no.
. Lanthanides and Actinides:
Lanthanides and Actinides are kept separately at the bottom of the table. They are placed in the f-block of the periodic table.
.Properties of elements:
Elements with the same properties are placed in the same group. For example, group 17 is of halogens which have similar chemical properties.
