Chapter 4, Problem 105A

Interpretation Introduction

Interpretation:

The effect of each type of radiation on atomic number and mass number of an atom needs to be described.

Concept introduction:

Radioactive decay can results in change in the protons in the nucleus. Also, the identity of an atom gets changed. The number of protons in an atom is called the atomic number. The sum of the number of protons and neutrons is equal to the mass number.

$Massnumber=Numberofprotons+Numberofneutrons$

Answer to Problem 105A

The radiation changes the atomic number and mass number of an atom. There are three types of radiation occurs, Alpha radiation, Beta radiation and Gamma radiation.

Explanation of Solution

The main three forms of radioactive emissions are as follows:

• Alpha particle emission.
• Beta particle emission.
• Gamma radiation.

An alpha particlecontains two protons and two neutrons similar to He atom.

When an alpha particle is emitted from radioactive atom, the first change isin the atomic number. It decreases by two, and its mass number is decreased by 4 units. For example the alpha-particle emissionis shown as follows:

₉₂²³⁵U → ₂⁴He+₉₀²³¹Th

The second radioactive emission is called a beta particle. A beta particle is formed after the removal of an electron from the nucleus with-1 charge. The new formed atom has same mass number, since, the number of protons increases by one unit, the atomic number increases by one. Example of emitting a beta particle is as follows:

₆¹⁴C →₇¹⁴N+_-1⁰e

The third type is not a particle but it is an energetic form of electromagnetic radiation. This is known as gamma rays. The atomic number and mass number does not change during this decay. It can takes place along with beta decay and alpha decay

The reactions are represented as follows:

${}_{27}^{60}\text{Co}{\to }_{28}^{60}{\text{Ni+}}_{-1}^{0}e+2_0^{0}Y$

$\begin{array}{l}{}_{53}^{125}{I}^{*}{\to }_{53}^{125}I+\gamma \\ {}_{88}^{226}Ra{\to }_{86}^{222}Rn{+}_2^{4}He{+}_0^0\gamma \end{array}$

Conclusion

From these types of radiation, the atomic number and mass number change.

The original atom’s atomic number decreases by two and its mass number decreases by four, when alpha radiation occurs. When beta decay takes place, the mass number remains the same but the number of protons increases by 1 unit. There is no change bygamma radiation.