Question

How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?

How could the modern periodic law remove various anomalies of Mendeleev's periodic table? Explain with examples.

Answer 1

1. Elements are arranged in the increasing order of their atomic number in Modern Periodic Table, thus there was no need for keeping more than one element in one slot.
2. The place of isotopes in the Modern Periodic Table was not a problem, as isotopes have the same atomic number but different atomic masses.
3. Elements having the same valence electron are kept in the same group.
4. Elements having the same number of shells were put under the same period.
5. The position of hydrogen became clarified as it was kept in the group with the elements of the same valence electrons.

Answer 2

As the modern periodic law is based on the atomic numbers of elements, all the anomalies of Mendeleev's periodic table are removed. For example:

1. The position of isotopes could be explained, which Mendeleev's periodic table failed to do. As all the isotopes of an element have the same atomic number, they can be placed in the same group in a periodic table.
   For example, Cl-35 and Cl-36, chlorine isotopes with the same atomic number 17, can be placed in the same group on the periodic table.
2. Mendeleev could not explain why cobalt was placed before nickel. The modern periodic law solved this problem. The atomic numbers of cobalt and nickel are 27 and 28, respectively. Hence, the modern periodic table placed cobalt with a lower atomic number before nickel.