This lesson uses the atomic-number rule to explain isotopes: same element, same protons, but different numbers of neutrons.
Use the PDF for classwork, homework or revision. It includes key ideas, activities, questions, an extend task and success-criteria proof.
Write a first response before reading. Then compare it with your answer at the end.
The key idea in this lesson is simple: isotopes keep the same proton number.
If two atoms have the same number of protons, they are the same element. If the neutron number differs, they are different isotopes of that element.
This is the cleanest way to stop students relying on mass number alone.
Neutrons change the mass number but not the element name.
That means carbon-12 and carbon-14 are both carbon because both still have six protons. The changing neutron count explains the different mass numbers.
The lesson stays conceptual and does not move into isotope abundance calculations.
Isotope questions are useful because they force students to apply the earlier rules carefully.
Ask first: are the proton numbers the same? If yes, the atoms are the same element. Then ask: are the neutron numbers different? If yes, they are isotopes.
This two-step check is more reliable than guessing from names or pictures.
Isotopes are not just abstract atom examples. They can be useful in the real world.
At Stage 4 level, students should know that some isotopes are used in medicine, tracing and imaging because scientific understanding of substances can change how people use them.
The emphasis is on the broad idea of use, not detailed nuclear science.
Copy the isotope rule in a way that makes the comparison easy to remember.
Same element means same number of protons.
Isotopes have different numbers of neutrons.
Different neutron numbers can change mass number without changing the element.
Compare three atom descriptions and decide which pair are isotopes. Explain your reasoning using proton number and neutron number.
Write a short explanation of why carbon-12 and carbon-14 are both carbon even though the numbers are different.
1. What makes two atoms isotopes of the same element?
2. Which number must stay the same for atoms to remain the same element?
3. If two atoms have the same atomic number but different mass numbers, what is the best conclusion?
4. Why can isotopes have different mass numbers?
5. Which is the best Stage 4 statement about isotope uses?
Define an isotope using proton number and neutron number.
Explain why two atoms with the same atomic number but different mass numbers can still be the same element.
Describe one broad real-world use of isotopes and explain why this matters for science learning.
1: D. Isotopes have the same proton number but different neutron numbers.
2: A. The proton number must stay the same.
3: B. Same atomic number but different mass number suggests isotopes.
4: C. Isotopes differ in neutron number, which changes mass number.
5: A. Some isotopes have practical uses such as tracing and medicine.
An isotope is an atom of the same element that has the same number of protons but a different number of neutrons.
They are still the same element because element identity depends on proton number. Different neutron numbers change the mass number, but not the atomic number.
One broad use is medical tracing or imaging. This matters because it shows that scientific understanding of atoms and substances can influence how materials are used in society.
Same protons, different neutrons.
Proton number decides the element.
Different neutron numbers can change mass number.
Some isotopes have practical roles in medicine and tracing.