Group Displacement Law

Group Displacement Law:

The results of α-particle and β-particle change have been summed up by Fazan, Russel and Soddy in the form of a law known as Group Displacement Law which states that “the α-particle emission from the nucleus of a radioactive substance (Parent element) results in the formation of a new element (daughter element) having atomic mass less by four units and is displaced two groups to the left of its parent element in the periodic table while β-particle emission results in the formation of a new element having same atomic mass but is displaced one group to the right of its parent element in the periodic table”. Example-

Thus, it follows from the above examples that one α-particle change followed by two β-particle changes results in the formation of “Isotopes” (different atoms of the same element having the same atomic number but different atomic mass) whereas one β-particle change results in the formation of “Isobars” (atoms of different elements having same atomic mass but different atomic numbers). So, in the above examples-

₈₄Po²¹⁵ ; ₈₄Po²¹¹ and ₉₀Th²³² ; ₉₀Th²²⁸ are Isotopes whereas ₈₂Pb²¹¹ , ₈₃Bi²¹¹ and ₈₄Po²¹¹ are Isobars. Similarly, ₈₈Ra²²⁸ , ₈₉Ac²²⁸ and ₉₀Th²²⁸ are also Isobars.