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Isotopes and Their Uses

2.4 Isotopes and Its Uses
CHEMISTRY • Form 4 • Chapter 2: Matter and the Atomic Structure

2.4Isotopes and Its Uses

Isotopes are atoms of the same element that share identical chemical properties due to having the same proton number, but possess different masses because of differing numbers of neutrons. In nature, most elements exist as mixtures of isotopes. Understanding isotopes allows us to calculate an element's relative atomic mass based on natural abundance and harness their unique properties in medicine, agriculture, industry, archaeology, and nuclear energy.

Learning Objectives

  • Deduce the meaning of isotopes.
  • Calculate the relative atomic mass of isotopes.
  • Justify the usage of isotopes in various fields.

Subatomic Comparison and Uses of Isotopes

Same protons, different neutrons — and a wide range of practical applications.

Chlorine-35
\(^{35}_{17}\text{Cl}\)
17 protons • 18 neutrons • 17 electrons
Chlorine-37
\(^{37}_{17}\text{Cl}\)
17 protons • 20 neutrons • 17 electrons
MedicineCobalt-60, Iodine-131
AgriculturePhosphorus-32
NuclearUranium-235
ArchaeologyCarbon-14, Lead-210
IndustryHydrogen-3
EngineeringSodium-24

Brief Explanation

Understand the meaning of isotopes and how their natural abundance determines relative atomic mass.

Isotopes are atoms of the same element with the same number of protons but different number of neutrons. Because they have the same proton number, they maintain identical chemical identities, but their different neutron counts give them different nucleon numbers and atomic masses.

Hydrogen Isotopes

Hydrogen exists as three isotopes: \(^{1}_{1}\text{H}\), \(^{2}_{1}\text{H}\), and \(^{3}_{1}\text{H}\). All three have the same proton number (1) but different nucleon numbers (1, 2, and 3).

Other Examples

Silicon: \(^{28}_{14}\text{Si}\), \(^{29}_{14}\text{Si}\), \(^{30}_{14}\text{Si}\)
Magnesium: \(^{24}_{12}\text{Mg}\), \(^{25}_{12}\text{Mg}\), \(^{26}_{12}\text{Mg}\)
Phosphorus: \(^{31}_{15}\text{P}\), \(^{32}_{15}\text{P}\)

Isotope Protons Neutrons Electrons
Chlorine-35 (\(^{35}_{17}\text{Cl}\)) 17 18 17
Chlorine-37 (\(^{37}_{17}\text{Cl}\)) 17 20 17
Relative atomic mass formula:
\[\text{Relative atomic mass} = \frac{\sum(\% \text{ isotope} \times \text{mass of isotope})}{100}\]

Worked Example

Chlorine consists of two isotopes: \(^{35}_{17}\text{Cl}\) (75%) and \(^{37}_{17}\text{Cl}\) (25%).

\[\text{Relative atomic mass of chlorine} = \frac{(75 \times 35) + (25 \times 37)}{100} = \frac{2625 + 925}{100} = \frac{3550}{100} = 35.5\]

Try These Questions First

Answer mentally, then check the explanation.

1

What is meant by isotopes?

Answer: Isotopes are atoms of the same element with the same number of protons but different number of neutrons.
2

State the isotope used in detecting leakages in underground pipes.

Answer: Sodium-24.
3

An element has two isotopes: isotope-X with a mass of 10 and an abundance of 20%, and isotope-Y with a mass of 11 and an abundance of 80%. What is the relative atomic mass of this element?

Answer: \(\frac{(20 \times 10) + (80 \times 11)}{100} = \frac{200 + 880}{100} = 10.8\).

Common Mistakes

Avoid these errors when working with isotopes.

!
Confusing the subatomic particles: Stating that isotopes have different numbers of protons instead of neutrons.
!
Forgetting to divide by 100 when calculating relative atomic mass using isotope percentages.
!
Confusing the specific medical uses of Cobalt-60 (cancer radiotherapy and tool sterilisation) with Iodine-131 (thyroid disorders).
!
Stating that isotopes have different chemical properties; isotopes have the same chemical properties because they have the same number of valence electrons and protons.

Common Misconceptions

Compare each misconception with the correct fact.

Misconception

Isotopes are different elements because their nucleon numbers are different.

Correct Fact

Isotopes belong to the same element because the identity of an element is determined solely by its proton number, which remains identical among isotopes.

Misconception

Relative atomic mass is just a simple average of the mass numbers of an element's isotopes.

Correct Fact

Relative atomic mass is a weighted average that depends directly on the percentage natural abundance of each isotope present in a natural sample.

Summary

Key facts to remember.

  • Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons.
  • Natural Abundance: Percentage of each isotope naturally present in an element sample.
  • Relative Atomic Mass Formula: \(\text{RAM} = \frac{\sum(\% \text{ isotope} \times \text{mass of isotope})}{100}\).
  • Key Isotope Uses: Medicine (Cobalt-60, Iodine-131), Agriculture (Phosphorus-32), Nuclear (Uranium-235), Archaeology (Carbon-14, Lead-210), Industry (Hydrogen-3), Engineering (Sodium-24).

Quick Activity

Complete all parts before checking your score.

A. Objective Quiz

1

Which of the following pairs of subatomic particles is identical in two isotopes of the same element?

2

Which isotope is correctly matched to its use in archaeology?

B. Fill in the Blanks

3

The percentage of isotopes present in a natural sample of an element is known as natural __________.

4

In medicine, the isotope __________ is used in radiotherapy to kill cancer cells without surgery and to sterilise surgical tools.

C. Match the Isotope with Its Application

Drag each isotope on desktop. On mobile, tap an isotope and then tap the matching box.

Isotope

Iodine-131 Phosphorus-32 Sodium-24 Hydrogen-3

Application

1Treatment of thyroid disorders such as hyperthyroidism and thyroid cancer
2Study of plant metabolism
3Detecting leakage in underground pipes
4Detector to study sewage and liquid wastes
Complete every answer before checking.
 

Keywords

Tap or hover over a term to read its meaning.

Isotopes Natural abundance Relative atomic mass Proton number Nucleon number Radiotherapy
The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of Pandai.

Isotopes and Their Uses

2.4 Isotopes and Its Uses
CHEMISTRY • Form 4 • Chapter 2: Matter and the Atomic Structure

2.4Isotopes and Its Uses

Isotopes are atoms of the same element that share identical chemical properties due to having the same proton number, but possess different masses because of differing numbers of neutrons. In nature, most elements exist as mixtures of isotopes. Understanding isotopes allows us to calculate an element's relative atomic mass based on natural abundance and harness their unique properties in medicine, agriculture, industry, archaeology, and nuclear energy.

Learning Objectives

  • Deduce the meaning of isotopes.
  • Calculate the relative atomic mass of isotopes.
  • Justify the usage of isotopes in various fields.

Subatomic Comparison and Uses of Isotopes

Same protons, different neutrons — and a wide range of practical applications.

Chlorine-35
\(^{35}_{17}\text{Cl}\)
17 protons • 18 neutrons • 17 electrons
Chlorine-37
\(^{37}_{17}\text{Cl}\)
17 protons • 20 neutrons • 17 electrons
MedicineCobalt-60, Iodine-131
AgriculturePhosphorus-32
NuclearUranium-235
ArchaeologyCarbon-14, Lead-210
IndustryHydrogen-3
EngineeringSodium-24

Brief Explanation

Understand the meaning of isotopes and how their natural abundance determines relative atomic mass.

Isotopes are atoms of the same element with the same number of protons but different number of neutrons. Because they have the same proton number, they maintain identical chemical identities, but their different neutron counts give them different nucleon numbers and atomic masses.

Hydrogen Isotopes

Hydrogen exists as three isotopes: \(^{1}_{1}\text{H}\), \(^{2}_{1}\text{H}\), and \(^{3}_{1}\text{H}\). All three have the same proton number (1) but different nucleon numbers (1, 2, and 3).

Other Examples

Silicon: \(^{28}_{14}\text{Si}\), \(^{29}_{14}\text{Si}\), \(^{30}_{14}\text{Si}\)
Magnesium: \(^{24}_{12}\text{Mg}\), \(^{25}_{12}\text{Mg}\), \(^{26}_{12}\text{Mg}\)
Phosphorus: \(^{31}_{15}\text{P}\), \(^{32}_{15}\text{P}\)

Isotope Protons Neutrons Electrons
Chlorine-35 (\(^{35}_{17}\text{Cl}\)) 17 18 17
Chlorine-37 (\(^{37}_{17}\text{Cl}\)) 17 20 17
Relative atomic mass formula:
\[\text{Relative atomic mass} = \frac{\sum(\% \text{ isotope} \times \text{mass of isotope})}{100}\]

Worked Example

Chlorine consists of two isotopes: \(^{35}_{17}\text{Cl}\) (75%) and \(^{37}_{17}\text{Cl}\) (25%).

\[\text{Relative atomic mass of chlorine} = \frac{(75 \times 35) + (25 \times 37)}{100} = \frac{2625 + 925}{100} = \frac{3550}{100} = 35.5\]

Try These Questions First

Answer mentally, then check the explanation.

1

What is meant by isotopes?

Answer: Isotopes are atoms of the same element with the same number of protons but different number of neutrons.
2

State the isotope used in detecting leakages in underground pipes.

Answer: Sodium-24.
3

An element has two isotopes: isotope-X with a mass of 10 and an abundance of 20%, and isotope-Y with a mass of 11 and an abundance of 80%. What is the relative atomic mass of this element?

Answer: \(\frac{(20 \times 10) + (80 \times 11)}{100} = \frac{200 + 880}{100} = 10.8\).

Common Mistakes

Avoid these errors when working with isotopes.

!
Confusing the subatomic particles: Stating that isotopes have different numbers of protons instead of neutrons.
!
Forgetting to divide by 100 when calculating relative atomic mass using isotope percentages.
!
Confusing the specific medical uses of Cobalt-60 (cancer radiotherapy and tool sterilisation) with Iodine-131 (thyroid disorders).
!
Stating that isotopes have different chemical properties; isotopes have the same chemical properties because they have the same number of valence electrons and protons.

Common Misconceptions

Compare each misconception with the correct fact.

Misconception

Isotopes are different elements because their nucleon numbers are different.

Correct Fact

Isotopes belong to the same element because the identity of an element is determined solely by its proton number, which remains identical among isotopes.

Misconception

Relative atomic mass is just a simple average of the mass numbers of an element's isotopes.

Correct Fact

Relative atomic mass is a weighted average that depends directly on the percentage natural abundance of each isotope present in a natural sample.

Summary

Key facts to remember.

  • Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons.
  • Natural Abundance: Percentage of each isotope naturally present in an element sample.
  • Relative Atomic Mass Formula: \(\text{RAM} = \frac{\sum(\% \text{ isotope} \times \text{mass of isotope})}{100}\).
  • Key Isotope Uses: Medicine (Cobalt-60, Iodine-131), Agriculture (Phosphorus-32), Nuclear (Uranium-235), Archaeology (Carbon-14, Lead-210), Industry (Hydrogen-3), Engineering (Sodium-24).

Quick Activity

Complete all parts before checking your score.

A. Objective Quiz

1

Which of the following pairs of subatomic particles is identical in two isotopes of the same element?

2

Which isotope is correctly matched to its use in archaeology?

B. Fill in the Blanks

3

The percentage of isotopes present in a natural sample of an element is known as natural __________.

4

In medicine, the isotope __________ is used in radiotherapy to kill cancer cells without surgery and to sterilise surgical tools.

C. Match the Isotope with Its Application

Drag each isotope on desktop. On mobile, tap an isotope and then tap the matching box.

Isotope

Iodine-131 Phosphorus-32 Sodium-24 Hydrogen-3

Application

1Treatment of thyroid disorders such as hyperthyroidism and thyroid cancer
2Study of plant metabolism
3Detecting leakage in underground pipes
4Detector to study sewage and liquid wastes
Complete every answer before checking.
 

Keywords

Tap or hover over a term to read its meaning.

Isotopes Natural abundance Relative atomic mass Proton number Nucleon number Radiotherapy
The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of Pandai.
Chapter : Matter and Atomic Structure
Topic : Isotopes and Its Uses
Form 4 Chemistry
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