Chapter 3, Problem 2SC

Interpretation Introduction

Interpretation:

The number of neutrons in an isotope $\text{Be-9}$ is to be determined.

Concept introduction:

 An atom consists of a nucleus and extranuclear space. The nucleus of an atom is composed of protons and neutrons while the extra nuclear space contains electrons.

 Atoms of an element can exist in more than one forms. Each form is termed as an isotope and differs from the other forms in the number of neutrons. The number of protons and electrons are equal in all the forms.

 Isotopes of an element are the species which contain the same number of protons as that element but a different number of neutrons. They are variants of the same element. The mass number of an atom is represented by $A$ and, because the atomic number is equal to the number of protons, it is represented by $Z$.

 So, the number of neutrons is calculated as follows:

$\begin{array}{c}\text{Number of neutrons}=\text{Mass number}-\text{Atomic number}\\ N=A-Z\end{array}$