Chapter 4, Problem 61A

How can you determine the number of neutrons in an atom if its mass number and its atomic number are known.

Interpretation Introduction

Interpretation:

The number of neutrons in an atom needs to be determined, if its Atomic number and Mass number are given.

Concept introduction:

Mass number is the total number of protons and neutrons present in the nucleus of an atom. Atomic number is also referred as number of protons in an atom.

The atomic symbol is represented as follows:

$\text{X}$

$\begin{array}{l}\text{A = Mass number}\hfill \\ \text{Z = Atomic number}\hfill \\ \hfill \end{array}$

Answer to Problem 61A

$\text{Number of neutrons = A - Z}$

Explanation of Solution

The atomic symbol is represented as follows:

$\text{X}$

Given,

$\begin{array}{l}\text{A = Mass number}\hfill \\ \text{Z = Atomic number}\hfill \\ \hfill \end{array}$

Atomic number is also referred as number of protons

$\text{Atomic number = number of protons }$

Mass number of an atom is calculated as follows:

$\begin{array}{l}\text{Mass number = Number of protons + Number of neutrons}\hfill \\ \therefore \text{Number of neutrons = Mass number – Number of protons}\hfill \end{array}$

Also,

Number of neutrons = Mass number − Atomic number

$\because \text{Atomic number = number of protons}$

$\text{Number of neutrons = A - Z}$

Conclusion

Thus, the total neutrons present in an atom can be determined by subtracting Atomic number from Mass number