Chapter 25, Problem 75A

Interpretation Introduction

Interpretation: The original nucleus has to be inferred.

Concept Introduction: When an atomic nucleus or more atomic nuclei and a subatomic particle collide, one or more nuclides also known as nuclear reactions are created.

Answer to Problem 75A

The original nucleus is astatine-215.

Explanation of Solution

According to nuclear reactions, the sum of the atomic number and mass number on the reactant side is equal to the sum of the atomic number and mass on the product side.

A radioactive nucleus decays to give a bismuth-211 and an alpha particle.

Let $\text{X}$ be the original nucleus with $\text{m}$ as its atomic number and $\text{n}$ as its mass number.

  ${}_{\text{m}}^{\text{n}}\text{X}{\to }_{83}^{211}\text{Bi}{+}_{\text{2}}^{\text{4}}\text{He}$   ...... (1)

Equate the values of the atomic number of the reactants and products.

  $\begin{array}{l}m=83+2\\ m=85\end{array}$

Equate the values of the mass number of the reactants and products.

  $\begin{array}{l}n=211+4\\ n=215\end{array}$

The element with atomic number 85 is Astatine $\left(\text{At}\right)$ .

The equation (1) is rewritten after the substitution of values.

  ${}_{85}^{215}\text{At}{\to }_{83}^{211}\text{Bi}{+}_{\text{2}}^{\text{4}}\text{He}$

The original nucleus is astatine-215.