Chapter 2, Problem 22QP

For each of the following species, determine the number of protons and the number of neutrons in the nucleus: $\text{H}\text{e,}\text{H}\text{e,}\text{M}\text{g,}\text{M}\text{g,}\text{B}\text{r,}\text{P}\text{t}\text{.}$

Interpretation Introduction

Interpretation: The number of protons and the number of neutronsin the various nuclei areto be determined.

Concept introduction:

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

The atomic number of a neutral atom is equalsto the number of protons present inside the nucleus.

Answer to Problem 22QP

Solution:

For ${}_{\text{2}}^{\text{3}}\text{He}$:

Number of neutrons $\text{= 1}$

Number of protons $\text{= 2}$

For ${}_{\text{2}}^4\text{He}$:

Number of neutrons $\text{= 2}$

Number of protons $\text{= 2}$

For ${}_{\text{12}}^{\text{24}}\text{Mg}$:

Number of neutrons $\text{= 12}$

Number of protons $\text{= 12}$

For ${}_{\text{12}}^{\text{25}}\text{Mg}$:

Number of neutrons $\text{= 13}$

Number of protons $\text{= 12}$

For ${}_{\text{22}}^{\text{48}}\text{Ti}$:

Number of neutrons $\text{= 26}$

Number of protons $\text{= 22}$

For ${}_{\text{35}}^{\text{79}}\text{Br}$:

Number of neutrons $\text{= 44}$

Number of protons $\text{= 35}$

For ${}_{\text{78}}^{\text{195}}\text{Pt}$:

Number of neutrons $\text{= 117}$

Number of protons $\text{= 78}$

Explanation of Solution

For ${}_{\text{2}}^{\text{3}}\text{He}$:

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons }\\ =3-2\\ =\text{1} \end{array}$

From the periodic table, the atomic number of helium is $\text{2}$.

Thus, the number of protons is equal to the atomic number that is $2$.

For ${}_{\text{2}}^4\text{He}$:

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons }\\ =4-2\\ =2 \end{array}$

From the periodic table, the atomic number of helium is $\text{2}$

Thus, the number of protons is equal to the atomic number that is $2$.

For ${}_{\text{12}}^{\text{24}}\text{Mg}$:

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons }\\ =24-12\\ =12 \end{array}$

From the periodic table, the atomic number of magnesium is $\text{12}$.

Thus, the number of protons is equal to the atomic number that is $12$.

For ${}_{\text{12}}^{\text{25}}\text{Mg}$:

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons }\\ =25-12\\ =13 \end{array}$

From the periodic table, the atomic number of magnesiumis $\text{12}$.

Thus, the number of protons is equal to the atomic number that is $12$.

For ${}_{\text{22}}^{\text{48}}\text{Ti}$:

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons }\\ =48-22\\ =26 \end{array}$

From the periodic table, the atomic number of titanium is $\text{22}$.

Thus, thenumber of protons is equal to the atomic number that is $22$.

For ${}_{\text{35}}^{\text{79}}\text{Br}$:

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons }\\ =79-35\\ =44 \end{array}$

From the periodic table, the atomic number of bromine is $35$.

Thus, the number of protons is equal to the atomic number that is $35$.

For ${}_{\text{78}}^{\text{195}}\text{Pt}$:

$\begin{array}{c}\text{Number of neutrons} =\text{Mass number }\left(A\right)-\text{Number of protons }\\ =195-78\\ =117 \end{array}$

From the periodic table, the atomic number of platinum is $78$.

Thus, the number of protons is equal to the atomic number that is $78$.

Conclusion

Number of protons and number of neutrons of all the given species are calculated as above.