Neutrons – Long Answer Questions
Medium Level (Application & Explanation)
Q1. Explain the discovery and basic properties of neutrons. Why was this discovery important?
Answer:
- Neutrons were discovered by J. Chadwick in 1932.
- A neutron has no charge. It is neutral.
- Its mass is almost equal to that of a proton.
- Neutrons are found in the nucleus of atoms.
- They are present in all atoms except hydrogen-1 (protium).
- This discovery explained atomic mass and nuclear stability better.
Q2. Why are neutrons essential for the stability of the nucleus? Use examples to explain.
Answer:
- Protons are positively charged and repel each other.
- Neutrons reduce this repulsion and help the nucleus stay stable.
- With too few or too many neutrons, the nucleus can be unstable.
- Unstable nuclei may show radioactive decay.
- Example: Carbon-12 (6p, 6n) is stable, but Carbon-14 (6p, 8n) is radioactive.
- Thus, neutrons act like the balancers inside the nucleus.
Q3. What is mass number? How do you calculate the number of neutrons in an atom?
Answer:
- The mass number (A) is the total of protons + neutrons.
- The atomic number (Z) is the number of protons.
- Number of neutrons (N) = A − Z.
- Example: For Carbon-12, A = 12 and Z = 6, so N = 6.
- Example: For Helium-4, A = 4 and Z = 2, so N = 2.
- This helps find how heavy an atom is and if it is an isotope.
Q4. What are isotopes? Explain with examples of carbon, chlorine, and hydrogen.
Answer:
- Isotopes are atoms of the same element with the same protons but different neutrons.
- They have the same atomic number but different mass numbers.
- Example: Carbon-12 (6n) and Carbon-14 (8n) are isotopes of carbon.
- Example: Chlorine-35 (18n) and Chlorine-37 (20n) are chlorine isotopes.
- Hydrogen has isotopes: protium (0n), deuterium (1n), tritium (2n).
- Isotopes have similar chemical behavior but different mass and sometimes stability.
Q5. Calculate neutrons and comment on stability: He-4, C-12, and Cl-37.
Answer:
- For Helium-4: Z = 2, A = 4, so neutrons N = 4 − 2 = 2.
- For Carbon-12: Z = 6, A = 12, so N = 12 − 6 = 6.
- For Chlorine-37: Z = 17, A = 37, so N = 37 − 17 = 20.
- He-4 and C-12 are stable with balanced proton–neutron ratios.
- Cl-37 is also stable, though heavier than Cl-35.
- Stability depends on a proper proton–neutron balance.
High Complexity (Analysis & Scenario-Based)
Q6. A new element has atomic number 12. You find two forms: A = 24 and A = 25. Explain what these forms are and how neutrons affect them.
Answer:
- Atomic number 12 means each atom has 12 protons.
- For A = 24, neutrons N = 24 − 12 = 12.
- For A = 25, neutrons N = 25 − 12 = 13.
- These are isotopes of the same element (same protons, different neutrons).
- They have the same chemical properties but different mass.
- The isotope with better proton–neutron balance is usually more stable.
Q7. A nucleus becomes radioactive due to neutron imbalance. Explain how this happens and what it leads to.
Answer:
- A stable nucleus needs a proper proton–neutron ratio.
- If there are too many or too few neutrons, it becomes unstable.
- Unstable nuclei try to gain stability by radioactive decay.
- They may change a neutron to a proton or the reverse in some decays.
- This changes the mass and sometimes the element itself.
- The process releases energy and radiation.
Q8. You are given a carbon sample. Test shows mass number 14. Explain what this means and how neutrons define this isotope.
Answer:
- Carbon has atomic number 6. So it has 6 protons.
- Mass number 14 means total nucleons are 14.
- Neutrons N = 14 − 6 = 8.
- This is Carbon-14, an isotope with extra neutrons.
- Carbon-14 is radioactive, while Carbon-12 is stable.
- Neutrons decide the isotope type, mass, and often stability.
Q9. Compare hydrogen isotopes: protium, deuterium, and tritium. How do neutrons change their properties?
Answer:
- Protium (¹H): 1 proton, 0 neutrons. It is most common and stable.
- Deuterium (²H): 1 proton, 1 neutron. Heavier and stable.
- Tritium (³H): 1 proton, 2 neutrons. Heaviest and radioactive.
- All three have similar chemical behavior (same protons).
- Their mass and stability differ because of neutrons.
- Neutrons change density, mass, and sometimes nuclear behavior.
Q10. A student says, “Neutrons do not matter because they have no charge.” Evaluate this statement with reasons and examples.
Answer:
- Neutrons have no charge, but they are still crucial.
- They add to the mass of the atom.
- They help overcome proton–proton repulsion and give stability.
- Without enough neutrons, nuclei become unstable and radioactive.
- Example: Carbon-12 is stable; Carbon-14 is not, due to neutron count.
- So, neutrons are essential for atomic mass, isotopes, and nuclear stability.