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SCI8 Q2W3D1: Isotopes - Definition and Significance

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Isotopes – Definition and Significance

🎯 Learning Goals

By the end of the lesson, you should be able to:

  1. Define isotopes and explain their significance in atomic structure with at least 80% accuracy.
  2. Differentiate isotopes of carbon (C-12, C-13, C-14) in terms of neutron number and mass number through a diagram-based activity.
  3. Illustrate isotopes of hydrogen (protium, deuterium, tritium) and label protons, neutrons, and electrons within 20 minutes of class activity.

🧩 Key Ideas & Terms

  • Isotopes – atoms of the same element with different numbers of neutrons
  • Protons – positively charged particles in the nucleus that determine the atomic number
  • Neutrons – neutral particles in the nucleus that vary in number among isotopes
  • Electrons – negatively charged particles orbiting the nucleus in shells
  • Mass Number – the sum of protons and neutrons in an atom

🔄 Prior Knowledge (Day 1)

Review what you already know about atomic structure and subatomic particles:

  1. What particle in the nucleus determines the identity of an element?
    Show AnswerProton
  2. Where are neutrons located in an atom?
    Show AnswerInside the nucleus
  3. What is the charge of an electron?
    Show AnswerNegative (-)

📖 Explore the Lesson – Day 1

Topic: Isotopes – Definition and Significance

1. Introduction: Revisiting the Atom 🧪

Every atom is made up of three main subatomic particles:

  • Protons (positive, inside the nucleus)
  • Neutrons (neutral, inside the nucleus)
  • Electrons (negative, orbiting the nucleus)

The atomic number of an element is defined by the number of protons. This number never changes for a given element. However, the number of neutrons can vary, leading to the existence of isotopes.

2. What are Isotopes? 🔬

Definition: Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons, which gives them different mass numbers.

  • Example:
    • Carbon-12 (C-12): 6 protons, 6 neutrons, 6 electrons
    • Carbon-14 (C-14): 6 protons, 8 neutrons, 6 electrons

Both are carbon because they have 6 protons, but they differ in their neutron count.

📌 Key point: Isotopes have the same chemical properties (because they have the same number of protons and electrons) but different physical properties due to varying masses.

3. Types of Isotopes ⚖️

  1. Stable Isotopes
    • Do not undergo radioactive decay.
    • Example: Carbon-12, Oxygen-16.
  2. Radioactive Isotopes (Radioisotopes)
    • Unstable and decay over time, emitting radiation.
    • Example: Carbon-14, Uranium-235.

4. Why Are Isotopes Important? 🌍

  • Archaeology: Carbon-14 is used in radiocarbon dating to determine the age of fossils and ancient artifacts (e.g., Dead Sea Scrolls ~2000 years old).
  • Medicine: Technetium-99m is used in imaging scans to diagnose cancer and heart disease.
  • Environmental Science: Oxygen isotopes are used to study past climates (paleoclimatology).
  • Nuclear Energy: Uranium-235 is used as fuel in nuclear power plants.

5. Worked Example: Hydrogen Isotopes 💧

Hydrogen has three isotopes:

  1. Protium (¹H): 1 proton, 0 neutrons
  2. Deuterium (²H): 1 proton, 1 neutron
  3. Tritium (³H): 1 proton, 2 neutrons
  • Protium is the most common and stable.
  • Deuterium is stable and found in heavy water.
  • Tritium is radioactive and used in nuclear fusion research.

6. Misconceptions About Isotopes 🚫

  • ❌ Misconception: “Isotopes of an element have different chemical properties.”
    ✅ Correction: They have the same chemical properties; differences are only in mass and stability.
  • ❌ Misconception: “Isotopes can change the element.”
    ✅ Correction: Only the number of protons defines the element, not neutrons.

7. Visual Representation (for classroom discussion) 🖼️

  • Carbon-12 atom: 6 protons, 6 neutrons, 6 electrons.
  • Carbon-14 atom: 6 protons, 8 neutrons, 6 electrons.

👉 Teacher draws both diagrams on the board and lets students compare.

8. Real-World Connection 🌐

  • Carbon dating was used to estimate the age of the Iceman (Ötzi), a mummy discovered in the Alps, at around 5,300 years old.
  • In nuclear medicine, PET scans use isotopes to detect cancer by highlighting high metabolic activity.

📚 References

  • Chang, R., & Goldsby, K.A. (2016). Chemistry (12th ed.). McGraw-Hill Education.
  • Hill, J.W., & Kolb, D.K. (2001). Chemistry for Changing Times (9th ed.). Prentice Hall.
  • U.S. Department of Energy. (n.d.). Isotope Basics. National Isotope Development Center. Retrieved from https://www.isotopes.gov/isotope-basics
  • Center for Environmental Studies. (n.d.). Isotopes and Temperature Measurement. NASA Global Climate Change Education Modules. https://www.ces.fau.edu/nasa/module-3/how-is-temperature-measured/isotopes.php
  • Elearnin. (2022). Uses of Radioactive Isotopes – Chemistry. YouTube. https://www.youtube.com/watch?v=E4B94zCY4ok

💡 Example in Action (Day 1)

Example 1:
Hydrogen has three isotopes. Draw protium (¹H), deuterium (²H), and tritium (³H) and label the protons, neutrons, and electrons.

Show Answer
  • Protium: 1 proton, 0 neutrons, 1 electron
  • Deuterium: 1 proton, 1 neutron, 1 electron
  • Tritium: 1 proton, 2 neutrons, 1 electron

👉 Now You Try 1:
Draw the isotopes of carbon (C-12, C-13, C-14). Label protons, neutrons, and electrons.

Show Answer
  • C-12: 6 protons, 6 neutrons, 6 electrons
  • C-13: 6 protons, 7 neutrons, 6 electrons
  • C-14: 6 protons, 8 neutrons, 6 electrons

Example 2:
Chlorine has two stable isotopes: Cl-35 (75%) and Cl-37 (25%). Which property makes them isotopes of the same element?

Show Answer They both have the same number of protons (17), which defines them as chlorine.

👉 Now You Try 2:
Oxygen has isotopes O-16, O-17, and O-18. What property do they share that makes them oxygen?

Show Answer They all have 8 protons, which defines them as oxygen.

Example 3:
Why do isotopes of the same element have the same chemical properties?

Show Answer Because they have the same number of protons and electrons, which determine chemical behavior.

👉 Now You Try 3:
Why does Carbon-14 differ from Carbon-12 if they both have 6 protons?

Show Answer They differ in neutron number (C-14 has 8 neutrons, while C-12 has 6), which affects their mass and stability.

Example 4:
Protium (¹H) is stable, but tritium (³H) is radioactive. Why?

Show Answer Tritium has too many neutrons, making the nucleus unstable and prone to radioactive decay.

👉 Now You Try 4:
Carbon-12 is stable, but Carbon-14 is radioactive. Why is C-14 unstable?

Show Answer Because it has 2 extra neutrons that make the nucleus unstable, causing it to decay over time.

Example 5:
In archaeology, radiocarbon dating uses C-14 to determine the age of fossils. Why is C-12 not used for dating?

Show Answer Because C-12 is stable and does not decay, while C-14 decays at a known rate, making it useful for dating.

👉 Now You Try 5:
In medicine, Technetium-99m is used for imaging, but Technetium-98 is not. Why do you think Tc-99m is chosen?

Show Answer Because Tc-99m is a radioactive isotope that emits detectable radiation safely in small doses, while Tc-98 is stable and not useful for imaging.

📝 Try It Out (Day 1)

Answer the following practice questions in your notebook.

  1. Define an isotope in your own words.
    Show Answer An isotope is an atom of the same element with the same number of protons but different numbers of neutrons.
  2. Which particle in an atom determines its identity as an element?
    Show Answer Proton
  3. Compare Carbon-12 and Carbon-14 in terms of neutron number.
    Show Answer C-12 has 6 neutrons; C-14 has 8 neutrons.
  4. Which isotope of hydrogen is radioactive: Protium, Deuterium, or Tritium?
    Show Answer Tritium
  5. Why do isotopes of an element have the same chemical properties?
    Show Answer Because they have the same number of protons and electrons.
  6. Oxygen has isotopes O-16, O-17, and O-18. Which property makes them all oxygen?
    Show Answer They all have 8 protons.
  7. Which isotope of Carbon is useful in radiocarbon dating?
    Show Answer Carbon-14
  8. Identify one isotope used in medical imaging.
    Show Answer Technetium-99m
  9. What is the difference between stable and radioactive isotopes?
    Show Answer Stable isotopes do not decay; radioactive isotopes are unstable and decay over time.
  10. Which subatomic particle varies in number among isotopes?
    Show Answer Neutrons

✅ Check Yourself (Day 1 Quiz)

Part A – Multiple Choice (5 items)

  1. Isotopes of an element have the same number of:
    1. Neutrons
    2. Protons
    3. Electrons
    4. Mass numbers
    Show Answerb) Protons
  2. Which isotope of hydrogen is radioactive?
    1. Protium
    2. Deuterium
    3. Tritium
    4. None of the above
    Show Answerc) Tritium
  3. Which subatomic particle differs among isotopes of the same element?
    1. Proton
    2. Electron
    3. Neutron
    4. Charge
    Show Answerc) Neutron
  4. Which isotope is commonly used in radiocarbon dating?
    1. Carbon-12
    2. Carbon-13
    3. Carbon-14
    4. Carbon-15
    Show Answerc) Carbon-14
  5. Which of the following is a stable isotope?
    1. Uranium-235
    2. Tritium
    3. Carbon-12
    4. Carbon-14
    Show Answerc) Carbon-12

Part B – True or False (5 items)

  1. Isotopes of an element always have different numbers of protons.
    Show AnswerFalse
  2. Carbon-12 and Carbon-14 are isotopes of the same element because they both have 6 protons.
    Show AnswerTrue
  3. The chemical properties of isotopes are determined by the number of neutrons.
    Show AnswerFalse
  4. Some isotopes are unstable and decay over time, releasing radiation.
    Show AnswerTrue
  5. Technetium-99m is a radioactive isotope used in medicine.
    Show AnswerTrue

Part C – Short Answer (5 items)

  1. Define isotope.
    Show AnswerAn isotope is an atom of the same element with the same number of protons but different numbers of neutrons.
  2. How do isotopes of carbon differ from each other?
    Show AnswerThey differ in their number of neutrons (C-12 has 6, C-13 has 7, C-14 has 8).
  3. Why do isotopes have the same chemical properties?
    Show AnswerBecause they have the same number of protons and electrons, which control chemical behavior.
  4. Give one isotope and its real-world application.
    Show AnswerCarbon-14 – radiocarbon dating; Technetium-99m – medical imaging.
  5. Which subatomic particle is responsible for atomic mass differences among isotopes?
    Show AnswerNeutrons

🚀 Go Further (Day 1)

Activity 1 – Poster Challenge 🎨
Create a poster showing at least three isotopes of one element. Label their protons, neutrons, and electrons. Include at least one real-world use for each isotope.

Show Example Carbon-12 (stable, photosynthesis), Carbon-13 (stable, isotope tracing), Carbon-14 (radioactive, radiocarbon dating).

Activity 2 – Isotope Detective 🔍
Research one radioactive isotope used in medicine. Write a short paragraph about:

  • Its properties
  • How it is used
  • Why it is important
Show Example Technetium-99m is used in imaging to detect cancer because it emits gamma rays detectable by scanners.

Activity 3 – Quick Compare ⚖️
Fill in the missing data for the following isotopes of Oxygen:

IsotopeProtonsNeutronsElectronsMass Number
O-168?816
O-178?817
O-188?818
Show Answer O-16 → 8 neutrons; O-17 → 9 neutrons; O-18 → 10 neutrons.

Activity 4 – Myth or Fact 🚫✔️
Decide whether the following statements are myths or facts:

  1. Isotopes have different numbers of protons.
  2. Isotopes have the same chemical properties.
  3. Isotopes can change into another element just by gaining neutrons.
Show Answer 1. Myth
2. Fact
3. Myth

Activity 5 – Application to Real Life 🌍
Write 3–4 sentences explaining why isotopes are important in at least one of these fields: archaeology, medicine, or energy production.

Show Example In archaeology, Carbon-14 is used in radiocarbon dating to determine the age of ancient fossils and artifacts. This helps scientists build timelines of human history.

🔗 My Reflection (Day 1)

Option A – Write 3–5 sentences ✍️
In your notebook, write 3–5 sentences reflecting on what you learned today about isotopes. You may include:

  • What new concept you understood
  • How isotopes are important in real life
  • Why isotopes still have the same chemical properties
Sample Reflection Today I learned that isotopes are atoms of the same element with different numbers of neutrons. I realized that while they have different masses, their chemical properties remain the same. I also found out that isotopes like Carbon-14 are very useful in archaeology for dating fossils and artifacts.

Option B – Checklist ✅
Check off what you can confidently say about isotopes:

  • ☐ I can define isotopes in my own words.
  • ☐ I can identify isotopes of carbon and hydrogen.
  • ☐ I can explain why isotopes have the same chemical properties.
  • ☐ I can give at least one real-life application of isotopes.
  • ☐ I can describe the difference between stable and radioactive isotopes.

All reflection answers must be written in the student's notebook.

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