8.3 Isotope
Atoms of the same element always possess the same number of protons. However, atoms of the same element can have different numbers of neutrons. These specific atoms are known as isotopes. Unstable isotopes emit radioactive radiation and are widely utilised in medicine, agriculture, food technology, industry, and power generation.
Learning Objectives
- Define isotopes and nucleon number accurately based on subatomic particles.
- Calculate or determine the number of protons, neutrons, and nucleon numbers for given isotopes.
- Explain the meaning of radioisotopes and identify their applications in various fields such as medicine, agriculture, food technology, archaeology, industry, and electricity generation.
Comparison of Subatomic Particles in Isotopes & Applications of Radioisotopes
Compare the structure of hydrogen isotopes and link each radioisotope to its field of application.
Short Explanation
Definition of Isotopes
Isotopes are atoms of the same element having the same number of protons but different numbers of neutrons.
Atoms of an element have the same number of protons and electrons, but some have different numbers of neutrons. The word isotope is derived from the Greek word ‘isos’ (meaning same) and ‘topos’ (meaning place), representing elements that occupy the same position in the Modern Periodic Table of Elements.
Nucleon Number and Representation
Isotopes are commonly written by their nucleon number. The nucleon number is the total number of protons and neutrons in the nucleus of that atom:
\[\text{Nucleon number} = \text{Number of protons} + \text{Number of neutrons}\]
For example, an isotope of hydrogen with 1 proton and 2 neutrons is written as hydrogen-3.
Examples of Isotopes
| Element | Isotope | Protons | Electrons | Neutrons | Nucleon number |
|---|---|---|---|---|---|
| Hydrogen | Hydrogen-1 | 1 | 1 | 0 | 1 |
| Hydrogen | Hydrogen-2 | 1 | 1 | 1 | 2 |
| Hydrogen | Hydrogen-3 | 1 | 1 | 2 | 3 |
| Carbon | Carbon-12 | 6 | 6 | 6 | 12 |
| Carbon | Carbon-13 | 6 | 6 | 7 | 13 |
| Carbon | Carbon-14 | 6 | 6 | 8 | 14 |
| Oxygen | Oxygen-16 | 8 | 8 | 8 | 16 |
| Oxygen | Oxygen-18 | 8 | 8 | 10 | 18 |
| Chlorine | Chlorine-35 | 17 | 17 | 18 | 35 |
| Chlorine | Chlorine-37 | 17 | 17 | 20 | 37 |
| Sodium | Sodium-23 | 11 | 11 | 12 | 23 |
| Sodium | Sodium-24 | 11 | 11 | 13 | 24 |
| Bromine | Bromine-79 | 35 | 35 | 44 | 79 |
| Bromine | Bromine-81 | 35 | 35 | 46 | 81 |
Use of Isotopes in Various Fields
Radioisotopes are unstable isotopes that emit radioactive radiation. Even though harmful, they have significant uses when handled correctly.
Medical field
Gamma radiation from cobalt-60 is used to kill cancer cells in a radiotherapy machine. Sodium-24 and iodine-131 are also used in medicine.
Agriculture
Phosphorus-32 is injected into plant roots to study the rate of absorption of phosphorus fertiliser in plants. Carbon-14 is also studied in agriculture.
Food technology
Gamma radiation from cobalt-60 is used to destroy microorganisms on vegetables without changing food quality.
Archaeology and geology
Carbon-14 is used in archaeology and geology for carbon dating.
Paper industry
Americium-241 is used in the paper industry.
Electricity generation
Uranium-235 is used in power generation.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What is the definition of isotopes?
An atom has 10 protons, 10 neutrons, and 10 electrons. What is the nucleon number of that atom?
State one use of cobalt-60 in the medical field.
Common Mistakes
- Confusing the number of neutrons with the nucleon number. The nucleon number is the total sum of protons plus neutrons, not just neutrons alone.
- Mistakenly including the number of electrons when calculating the nucleon number. Electrons are outside the nucleus and are not nucleons.
- Thinking isotopes of the same element have different numbers of protons. Protons must strictly remain identical for the same element.
Concept Misunderstandings
Isotopes are entirely different chemical elements because their nucleon numbers differ.
They belong to the very same element and have identical positions on the Periodic Table because they share identical proton numbers.
All radiation from radioisotopes is destructive and has no beneficial use.
When handled correctly and under controlled conditions, radioisotopes provide essential beneficial applications in radiotherapy, agriculture research, and food sterilisation.
Summary
- Isotopes: Atoms of the same element with identical proton numbers but different neutron numbers.
- Nucleon number: \(\text{Protons} + \text{Neutrons}\).
- Radioisotopes: Unstable isotopes emitting radioactive radiation.
- Key radioisotopes & applications:
- Cobalt-60: Radiotherapy to kill cancer cells; food irradiation to destroy microorganisms.
- Phosphorus-32: Studying plant absorption rates of phosphorus fertiliser.
- Uranium-235: Electricity generation.
- Americium-241: Paper industry.
- Carbon-14: Archaeology, geology, and agriculture.
- Iodine-131 & Sodium-24: Medical applications.
Short Activity
A. Objective Quiz
1 What subatomic particle differs in quantity between isotopes of the same element?
2 Which radioisotope is injected into plant roots to study the rate of absorption of phosphorus fertiliser?
B. Fill in the Blanks
3 The nucleon number is calculated by adding the number of protons and the number of in the nucleus of an atom.
4 Gamma radiation emitted from is used to destroy microorganisms on vegetables without affecting food quality.
C. Drag and Drop: Match Each Radioisotope to Its Application
Drag each radioisotope to its corresponding application or field. On a phone, tap an answer first, then tap a matching box. Tap the Answer Choices area to return a selected item.
C. Match Each Radioisotope to Its Application
Write the correct radioisotope next to each application.
| Application / Field | Radioisotope |
|---|---|
| 1. Used to kill cancer cells in radiotherapy | |
| 2. Studies the absorption rate of fertiliser in plant roots | |
| 3. Used in electricity and power generation | |
| 4. Used in the paper industry |
Answer choices: Cobalt-60 • Phosphorus-32 • Uranium-235 • Americium-241
