Chapter 2, Problem 28QP

Interpretation Introduction

Introduction:

The number of neutrons present in the given isotopes is to be determined.

Concept introduction:

The number of neutrons in an atom is defined as the difference between the mass number and the number of protons..

The atomic number $\text{(Z)}$ is the number of protons in the nucleus of each atom of an element.

The mass number $\text{(A)}$ is the total number of neutrons and protons present in the nucleus of an atom of an element. The expression for mass number is as follows:

mass number $\text{(A)}$ = number of protons $\text{(Z)}$ + number of neutrons

The accepted way to denote the atomic number and mass number of an atom of an element (X) is as follows:

${}_{\text{Z}}^{\text{A}}\text{X}$

Here, $\text{A}$ is mass number and $\text{Z}$ is atomic number.

Answer to Problem 28QP

Solution: 119, 27, 33, 9, 72, 78, 23, 24, 13, 17, 47, 56

Explanation of Solution

For ${}_{\text{79}}^{\text{198}}\text{Au}$:

From the periodic table, the atomic number of gold is $79$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =198-79\\ =119 \end{array}$

For ${}_{\text{20}}^{\text{47}}\text{Ca}$:

From the periodic table, the atomic number of calcium is $20$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =47-20\\ = 27 \end{array}$

For ${}_{\text{27}}^{\text{60}}\text{Co}$:

From the periodic table, the atomic number of cobalt is $27$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =60-27\\ = 33 \end{array}$

For ${}_{\text{9}}^{\text{18}}\text{F}$:

From the periodic table, the atomic number of fluorine is $9$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =18-9\\ = 9 \end{array}$

For ${}_{\text{53}}^{\text{125}}\text{I}$:

From the periodic table, the atomic number of iodine is $53$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =125-53\\ = 72 \end{array}$

For ${}_{\text{53}}^{\text{131}}\text{I}$:

From the periodic table, the atomic number of iodine is $53$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =131-53\\ = 78 \end{array}$

For ${}_{\text{19}}^{\text{42}}\text{K}$:

From the periodic table, the atomic number of potassium is $19$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =42-19\\ = 23 \end{array}$

For ${}_{\text{19}}^{\text{43}}\text{K}$:

From the periodic table, the atomic number of potassium is $19$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =43-19\\ = 24 \end{array}$

For ${}_{\text{11}}^{\text{24}}\text{Na}$:

From the periodic table, the atomic number of potassium is $19$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =24-11\\ = 13 \end{array}$

For ${}_{\text{15}}^{\text{32}}\text{P}$:

From the periodic table, the atomic number of phosphorus is $15$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =32-15\\ = 17 \end{array}$

For ${}_{\text{38}}^{\text{85}}\text{Sr}$:

From the periodic table, the atomic number of strontium is $38$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =85-38\\ = 47 \end{array}$

For ${}_{\text{43}}^{\text{99}}\text{Tc}$:

From the periodic table, the atomic number of potassium is $19$.

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons}\\ =99-43\\ = 56 \end{array}$

Conclusion

For ${}_{\text{79}}^{\text{198}}\text{Au}$: Number of neutrons $\text{= 119}$.

For ${}_{\text{20}}^{\text{47}}\text{Ca}$:Number of neutrons $\text{= 27}$.

For ${}_{\text{27}}^{\text{60}}\text{Co}$:Number of neutrons $\text{= 33}$.

For ${}_{\text{9}}^{\text{18}}\text{F}$:Number of neutrons $\text{= 9}$.

For ${}_{\text{53}}^{\text{125}}\text{I}$:Number of neutrons $\text{= 72}$.

For ${}_{\text{53}}^{\text{131}}\text{I}$:Number of neutrons $\text{= 78}$.

For ${}_{\text{19}}^{\text{42}}\text{K}$:Number of neutrons $\text{= 23}$.

For ${}_{\text{19}}^{\text{43}}\text{K}$:Number of neutrons $\text{= 24}$.

For ${}_{\text{11}}^{\text{24}}\text{Na}$:Number of neutrons $\text{= 13}$.

For ${}_{\text{15}}^{\text{32}}\text{P}$:Number of neutrons $\text{= 17}$.

For ${}_{\text{38}}^{\text{85}}\text{Sr}$:Number of neutrons $\text{= 47}$.

For ${}_{\text{43}}^{\text{99}}\text{Tc}$:Number of neutrons $\text{= 56}$.