Chapter 10, Problem 10.25P

Compare fluorine-18 and fluorine-19 with regard to each of the following:

1. atomic number;
2. number of protons;
3. number of neutrons;
4. mass number. Give the isotope symbol for each isotope. F-19 is a stable nucleus and F-18 is used in PET scans.

Interpretation Introduction

(a)

Interpretation:

The atomic number of fluorine-18 and fluorine-19 should be compared.

Concept Introduction:

The number of protons indicates the atomic number of the element. It defines its characteristic place in the periodic table.

Answer to Problem 10.25P

The atomic numbers of fluorine-18 and fluorine-19 are same.

Explanation of Solution

Elements having two or more forms in which the numbers of protons are the same but the number of neutrons is different in the nuclei is said to be the isotopes.

The isotopes of fluorine have mass numbers 18 and 19.

Since the isotope of an element has same number of protons (which represents atomic number of the element) and the atomic number of fluorine is 9.

Hence, both the isotopes have the same atomic number.

Interpretation Introduction

(b)

Interpretation:

The number of protons of fluorine-18 and fluorine-19 should be compared.

Concept Introduction:

The number of protons indicates the atomic number. It is present along with the neutrons in the nucleus of the atom. The protons are positively charged particles.

Answer to Problem 10.25P

The number of protons is the same for fluorine-18 and fluorine-19.

Explanation of Solution

Elements having two or more forms in which the numbers of protons are the same but the number of neutrons is different in the nuclei is said to be the isotopes.

Since the isotope of an element has the same number of protons (which represents the atomic number of the element) and the atomic number of fluorine is 9 so, the number of protons for all the isotopes of fluorine is 9.

Interpretation Introduction

(c)

Interpretation:

The number of neutrons of fluorine-18 and fluorine-19 should be compared.

Concept Introduction:

The mass number is the total number of protons and neutrons present in the nucleus. Both constitute the mass of the element. Besides neutrons are neutrally charged particles.

Answer to Problem 10.25P

The number of neutrons in fluorine-18 is 9 and the number of neutrons in fluorine-19 is 10

Explanation of Solution

The number of neutrons is computed from the mass number of the element

The number of protons in fluorine-18 is 9:

  $\begin{array}{c}\text{Number of neutrons= Mass number - number of protons}\\ \text{= 18 - 9}\\ =9\end{array}$

The number of protons in fluorine-19 is 9:

  $\begin{array}{c}\text{Number of neutrons= Mass number - number of protons}\\ \text{= 19 - 9}\\ =10\end{array}$

Interpretation Introduction

(d)

Interpretation:

The mass number of fluorine-18 and fluorine-19 should be compared and the symbol of each isotope of fluorine should be determined.

Concept Introduction:

The mass number is the total number of protons and neutrons present in the nucleus. Both added together will total to give mass of the element.

The isotope of any element is indicated by its atomic number and mass number. Both the numbers are displayed along with the element. The mass number is displayed as superscript while the atomic number is displayed as subscript as shown

  $\text{E}\text{lement}$

Answer to Problem 10.25P

The mass number of fluorine-18 is 18 and fluorine-19 is 19.

  $F$ and $F$ are the isotopic symbol of fluorine-18 and fluorine-19 respectively.

Explanation of Solution

It is known that mass number is the sum of number of protons and neutrons.

But the number indicated on the top left defines its mass number. Hence, for fluorine-18 is 18 and fluorine-19 is 19.

Number of proton for fluorine = atomic number = 9

Fluorine with mass number 18:

  $\begin{array}{l}\text{Mass number = 18}\\ \text{Atomic number = 9}\end{array}$

This is indicated as $F$.

Fluorine with mass number 19:

  $\begin{array}{l}\text{Mass number = 19}\\ \text{Atomic number = 9}\end{array}$

This is indicated as $F$.