Question

State the modern periodic law. How does this law iron out the deficiencies of Mendeleev's periodic table with respect to the placement of isotopes? Explain with an example.

Answer 1

Modern periodic law:

• Modern periodic law states that "The physical and chemical properties of the elements are periodic classification of their atomic numbers."

Placement of Isotope:

• Isotopes are the elements that have the same atomic numbers but different atomic mass numbers and Physical Properties.
• Elements were placed based on their atomic masses in Mendeleev's periodic table. So, one element would occupy two positions in Mendeleev's periodic table.
• So it is difficult to place an isotope in Mendeleev's periodic table because of their atomic masses.
• But in modern law, elements were placed based on their atomic numbers.
• Because isotopes have the same atomic numbers, there is no need to place an isotope in the modern periodic table.
• Hence, the deficiencies of Mendeleev's periodic table for placement of Isotopes were solved by this modern periodic law.