(a) How could the modern periodic law remove various anomalies of Mendeleev’s periodic table? Explain with examples. (b) Is it possible to have an element having atomic number 1.5 placed between hydrogen and helium?
(a) How could the modern periodic law remove various anomalies of Mendeleev’s periodic table? Explain with examples. (b) Is it possible to have an element having atomic number 1.5 placed between hydrogen and helium?

(a) Anomalies of Mendeleev’s periodic table:

1. Elements are arranged in increasing order of atomic number in modern periodic table, thus there was no need for keeping more than one element in one slot.

2. Mendeleev failed to explain the position of isotope whereas the modern periodic table puts them in one place in the same group.

3. Hydrogen has been placed at the top of the group 1, i.e. above the alkali metals with its properties similar to the alkali metal properties.

(b) Atomic number is always a simple whole number. There can be no element with atomic number 1.5 or fraction.