Chapter 2, Problem 2.15QP

Interpretation Introduction

Interpretation:

The number of protons, neutrons and electrons in given species has to be identified.

Concept Introduction:

Mass number(A): Mass number of an element is sum of protons and neutrons of the atom.

$\text{A= Number of protons}\left(\text{P}\right)\text{ + Number of neutrons}\left(\text{n}\right)$

Consider an element X with atomic number and mass number,

${}_Z^A\text{X}$

Where, A is mass number and Z is atomic number (number of proton or electron)

Answer to Problem 2.15QP

Number of proton, neutron and electrons for given species are given as follows.

Isotopes	${}_{\text{2}}^3\text{He}$	${}_{\text{2}}^4\text{He}$	${}_{\text{12}}^{\text{24}}\text{Mg}$	${}_{\text{12}}^{\text{25}}\text{Mg}$	${}_{\text{22}}^{\text{48}}\text{Ti}$	${}_{\text{35}}^{\text{79}}\text{Br}$	${}_{\text{78}}^{\text{195}}\text{Pt}$
No. of Protons	2	2	12	12	22	35	78
No. of Neutrons	1	2	12	13	26	44	117

Explanation of Solution

For ${}_{\text{2}}^3\text{He}$, the number of protons, neutrons, and electrons is calculated as follows,

$\begin{array}{c}{}_{\text{Z}}^{\text{A}}{\text{X = }}_{\text{2}}^{\text{3}}\text{He}\\ \text{Z (atomic number) = Number of protons}\\ \text{= 2}\\ \text{A (mass number) = Number of protons (P) + Number of neutrons (N)}\\ \text{ 3 = 2 + n }\\ \text{n}\text{=1}\end{array}$

Thus, the number of neutrons, protons and electrons are found as $1$, $2$ and $2$ respectively.

For ${}_{\text{2}}^4\text{He}$, the number of protons, neutrons, and electrons is calculated as follows,

$\begin{array}{c}{}_{\text{Z}}^{\text{A}}{\text{X = }}_{\text{2}}^4\text{He}\\ \text{Z (atomic number) = Number of protons}\\ \text{= 2}\\ \text{A (mass number) = Number of protons (P) + Number of neutrons (N)}\\ \text{ 4 = 2 + n }\\ \text{n}\text{=2}\end{array}$

Thus, the number of neutrons, protons and electrons are found as $2$, $2$ and $2$ respectively.

For ${}_{\text{12}}^{\text{24}}\text{Mg}$, the number of protons, neutrons, and electrons is calculated as follows,

$\begin{array}{c}{}_{\text{Z}}^{\text{A}}{\text{X = }}_{\text{12}}^{\text{24}}\text{Mg}\\ \text{Z (atomic number) = Number of protons}\\ \text{= 12}\\ \text{A (mass number) = Number of protons (P) + Number of neutrons (N)}\\ \text{ 24 = 12 + n }\\ \text{n}\text{=12}\end{array}$

Thus, the number of neutrons, protons and electrons are found as $12$, $12$ and $12$ respectively.

For ${}_{\text{12}}^{\text{25}}\text{Mg}$, the number of protons, neutrons, and electrons is calculated as follows,

$\begin{array}{c}{}_{\text{Z}}^{\text{A}}{\text{X = }}_{\text{12}}^{\text{25}}\text{Mg}\\ \text{Z (atomic number) = Number of protons}\\ \text{= 12}\\ \text{A (mass number) = Number of protons (P) + Number of neutrons (N)}\\ \text{ 25 = 12 + n }\\ \text{n}\text{=13}\end{array}$

Thus, the number of neutrons, protons and electrons are found as $13$, $12$ and $12$ respectively.

For ${}_{\text{22}}^{\text{48}}\text{Ti}$, the number of protons, neutrons, and electrons is calculated as follows,

$\begin{array}{c}{}_{\text{Z}}^{\text{A}}{\text{X =}}_{\text{22}}^{\text{48}}\text{Ti}\\ \text{Z (atomic number) = Number of protons}\\ \text{= 22}\\ \text{A (mass number) = Number of protons (P) + Number of neutrons (N)}\\ \text{ 48 = 22 + n }\\ \text{n}\text{=26}\end{array}$

Thus, the number of neutrons, protons and electrons are found as $26$, $22$ and $22$ respectively.

For ${}_{35}^{79}\text{Br}$, the number of protons, neutrons, and electrons is calculated as follows,

$\begin{array}{c}{}_{\text{Z}}^{\text{A}}{\text{X =}}_{35}^{79}\text{Br}\\ \text{Z (atomic number) = Number of protons}\\ \text{= 35}\\ \text{A (mass number) = Number of protons (P) + Number of neutrons (N)}\\ \text{ 79 = 35 + n }\\ \text{n}\text{= 44}\end{array}$

Thus, the number of neutrons, protons and electrons are found as $44$, $35$ and $35$ respectively.

For ${}_{\text{78}}^{\text{195}}\text{Pt}$, the number of protons, neutrons, and electrons is calculated as follows,

$\begin{array}{c}{}_{\text{Z}}^{\text{A}}{\text{X = }}_{\text{78}}^{\text{195}}\text{Pt}\\ \text{Z (atomic number) = Number of protons}\\ \text{= 78}\\ \text{A (mass number) = Number of protons (P) + Number of neutrons (N)}\\ \text{ 195 = 78 + n }\\ \text{n}\text{= 117}\end{array}$

Thus, the number of neutrons, protons and electrons are found as $117$, $78$ and $78$ respectively.

Conclusion

The number of protons, neutrons and electrons in given species were identified.