State Mendeleev's law and write a short note on Mendeleev's Periodic table with its limitations.
Answers
The following pairs of elements don’t follow the follow Mendeleev’s Principles:
Cobalt (58.9) with a higher atomic mass precedes Nickel (58.6) in the periodic table.
Tellurium (127.6) with a higher atomic mass than Iodine (126.9) precedes it in the periodic table.
Grouping of chemically dissimilar elements
Elements such as Copper and Silver bear no resemblance with the alkali metals, but they have been placed together in the first group.
Position of Isotopes
According to Mendeleev’s Periodic Law, isotopes of an element must be given separate places in the periodic table because they have different atomic masses.
Electronic arrangement
It does not explain the electronic arrangement of elements.
Separation of chemically similar elements
Elements that are chemically similar such as Gold and Platinum have been placed in separate groups.
The position of hydrogen
Hydrogen was not given a fixed position because it was considered in Group IA as well as in Group VIIA.
Answer:
Mendeleev's law
the law that the properties of the elements are periodic functions of their atomic numbers. Also called Mendeleev's law. (originally) 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.
Limitations of the Mendeleev periodic table are listed below.
Elements with large differences in properties were included in the same group. for example, hard metals like copper and silver were included along with soft metals like sodium and potassium.
No proper position could be given to the element hydrogen. In the periodic table, the location of hydrogen is uncertain. It was put with alkali metals within 1A class, but certain hydrogen properties are close to those of halogens. So, it can also be put for halogens in the band.
The increasing order of atomic mass was not strictly followed throughout. For example in cobalt and nickel & Tellurium and Indium.
As isotopes are atoms of the same element having different atomic masses, they should have been given different positions while arranging them in the order of atomic mass. But this was not done.