Important Concepts and Sample Problems on Atoms and Nuclei
FAQs on Atoms and Nuclei: Practice Questions and Answers
1. What is the difference between an atom and a nucleus?
An atom is the smallest unit of matter, while the nucleus is the central part of the atom containing protons and neutrons.
Key points:
- Atoms consist of a nucleus (with protons & neutrons) and electrons.
- The nucleus accounts for most of the atom's mass but is much smaller in size.
- Electrons revolve around the nucleus in finite energy levels (shells).
2. What are the main features of Rutherford’s atomic model?
Rutherford’s model describes an atom as mostly empty space with a small, dense, positively charged nucleus.
Main features:
- The nucleus contains most of the atom's mass and all positive charge.
- Electrons revolve around the nucleus in orbits.
- The diameter of the nucleus is much smaller than that of the atom.
3. What is mass defect and binding energy in a nucleus?
Mass defect is the difference between the sum of the individual masses of nucleons and the actual mass of the nucleus, while binding energy is the energy needed to separate a nucleus into its constituent protons and neutrons.
Key points:
- Mass defect is converted into binding energy according to Einstein’s equation E = mc2.
- Higher binding energy means a more stable nucleus.
4. Explain the process of nuclear fission with an example.
Nuclear fission is the splitting of a heavy nucleus into two lighter nuclei, releasing energy.
Example:
- When Uranium-235 absorbs a neutron, it splits into Barium-141, Krypton-92, three neutrons, and a large amount of energy.
- This process is harnessed in nuclear reactors and atomic bombs.
5. What is the difference between nuclear fusion and fission?
Nuclear fusion joins two light nuclei to form a heavier nucleus, whereas nuclear fission splits a heavy nucleus into lighter ones.
Major differences:
- Fusion occurs naturally in stars (like the Sun); fission occurs in reactors and bombs.
- Fusion releases more energy than fission.
- Fusion requires extremely high temperature and pressure.
6. What are isotopes, isobars, and isotones?
Isotopes are atoms of the same element with different numbers of neutrons, isobars have the same mass number but different atomic numbers, and isotones have the same number of neutrons but different mass numbers.
Definitions:
- Isotopes: Identical atomic number, different mass number (e.g., Carbon-12, Carbon-14).
- Isobars: Same mass number (A), different proton number (Z). (e.g., Argon-40 and Calcium-40).
- Isotones: Same number of neutrons.
7. Describe radioactivity and its types.
Radioactivity is the spontaneous emission of particles or radiation from unstable atomic nuclei.
Types of radioactivity:
- Alpha (α) decay: Emission of helium nuclei (2 protons + 2 neutrons).
- Beta (β) decay: Emission of electrons or positrons.
- Gamma (γ) decay: Emission of high-energy photons.
8. What is the significance of the binding energy per nucleon curve?
The binding energy per nucleon curve shows the stability of nuclei as a function of mass number.
Key points:
- Elements with the highest binding energy per nucleon (e.g., iron) are most stable.
- The curve explains why energy is released in both fusion of light nuclei and fission of heavy nuclei.
9. How is radioactivity measured and what are its applications?
Radioactivity is measured using instruments like the Geiger-Müller counter and scintillation detector.
Main applications:
- Medical diagnosis (e.g., cancer treatment using radiotherapy).
- Industrial uses (e.g., thickness measurement).
- Carbon dating for archaeological age estimation.
10. What are the safety measures for handling radioactive materials?
Safety measures are essential to minimise the harmful effects of radioactive exposure.
Important precautions:
- Use lead shields and protective clothing.
- Handle radioactive materials with remote tools or robotic arms.
- Store substances in shielded containers.
- Follow strict time, distance, and shielding protocols to limit exposure.
