Group Displacement Law

Group displacement law

source : sciencehq.com

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         Soddy, Fajan & Russel gave a law, to know the position of new element formed after the emission of  alpha & beta particle. According to Group displacement law.

• If an α-particle is emitted by a radio active element from its nucleus, the atomic no. of new element or daughter element formed is decreased by 2 units & atomic weight is decreased by 4 units. Therefore  the position of new element formed is displaced by two groups towards the left in the periodic table

_ZA^M——>_Z-2C^M-4 +₂He⁴ (α-particle)

• If a β–particle is emitted by a radioactive element, the atomic number of daughter element or new element is increased by one unit. Therefore the position of new element is displaced by one group towards the right in periodic table.

_ZA^M——> _Z+1C^M + _-1β⁰ (β-particle)

• If an α-particle is emitted from the nucleus of radioactive element and then 2β-particles are emitted in next two transformations, the daughter element is an isotope of parent element. The daughter & parent element have the same atomic number. Hence according to Group displacement law position of daughter & parent element in the periodic table will remain same.

_ZA^M—–> _ZA^M-4 +2_-1β⁰+₂He⁴

• Group displacement law is not applicable to lanthanides & actinides. (f-block elements)

Question 1 ) ₈₄Po²¹⁵ emits an α–particle from its nucleus. Find the position of new element in the periodic table. Polonium is present in 6^th group of periodic table.

Solution )

When α-particle is emitted, the atomic No. of new element is decreased by 2 units & atomic weight by 4 units. Its position is displaced by two group towards left in periodic table

₈₄Po^{215 ——->}    ₈₂Pb²¹¹+ ₂He⁴(α-particle)

(VI Group)       (IV group)

New element ₈₂Pb²¹¹ is present in IV group of periodic table.

1. ₈₃x^{209—alpha—->} Y   – -beta–>   Z

(V group)                    (III group)    (IV group)

Question 2 ) What is the atomic number & mass no. of daughter elements. Find their position in periodic table X is present in Vth group of periodic table.

Solution )

₈₃x²⁰⁹ — alpha—–>₈₁Y^{205  —beta——>} ₈₂Z²⁰⁵

(V group)         (III group)    (IV group)