24.121 CP - Chemistry: Molecular Nature Of Matter And Change

Question

A decay series starts with the synthetic isotope ₉₂²³⁹U. The first four steps are emissions of a particle ${\beta }^{-}$, another ${\beta }^{-}$, an $\alpha$particle, and another $\alpha$. Write a balanced nuclear equation for each step. Which natural series could start by this sequence?

Step-by-Step Solution

Answer

(1) ${}_{92}{}^{239}U{\to }_{93}^{239}Np{+}_{-1}^0\beta$

(2) ${}_{93}{}^{239}Np{\to }_{-1}^0\beta {+}_{94}^{239}Pu$

(3) ${}_{94}{}^{239}Pu{\to }_2^4\alpha {+}_{92}^{235}U$

(4) data-custom-editor="chemistry" ${}_{92}{}^{235}U{\to }_2^4\alpha {+}_{90}^{231}Th$

The series 4n can now begin.

Step 1: Definition of Isotope

Isotopes are chemical elements that have the same number of protons and electrons but differ in the number of neutrons they have.

Step 2: Determining balanced nuclear equation

The Np atom is produced via the first beta decay. 

${}_{92}{}^{239}U{\to }_{93}^{239}Np{+}_{-1}^0\beta$

The degradation of Np results in the formation of Pu.

${}_{93}{}^{239}Np{\to }_{-1}^0\beta {+}_{94}^{239}Pu$

Pu decays to U with alpha decay.

${}_{94}{}^{239}Pu{\to }_2^4\alpha {+}_{92}^{235}U$

Uranium is broken down into a Thorium atom and an alpha particle.

${}_{92}{}^{235}U{\to }_2^4\alpha {+}_{90}^{231}Th$

Step 3: Determining which natural series starts

Because the resulting atom is${}_{90}{}^{231}Th$ , the natural series can begin with it. The decay might begin in either the thorium or 4n series.