20 important questions and answers for the Class 9 Science chapter “Structure of the Atom”:
1. What is an atom?
Answer: An atom is the smallest unit of an element that retains the chemical properties of that element. It consists of a nucleus surrounded by electrons.
2. What are the main components of an atom?
Answer: The main components of an atom are:
- Nucleus: Contains protons and neutrons.
- Electrons: Negatively charged particles that orbit the nucleus.
3. What is the charge of a proton?
Answer: A proton has a positive charge of +1 elementary charge.
4. What is the charge of an electron?
Answer: An electron has a negative charge of -1 elementary charge.
5. What is the charge of a neutron?
Answer: A neutron has no charge; it is neutral.
6. Describe the Rutherford gold foil experiment.
Answer: Rutherford’s experiment involved directing alpha particles at a thin gold foil. Most particles passed through, but some were deflected at large angles. This led to the conclusion that the atom has a small, dense nucleus.
7. What did Rutherford’s experiment reveal about the atom’s structure?
Answer: It revealed that the atom has a small, dense, positively charged nucleus at its center, with electrons orbiting around it.
8. What is the Bohr model of the atom?
Answer: The Bohr model proposed that electrons orbit the nucleus in specific, quantized orbits or energy levels, and they can move between these levels by absorbing or emitting energy.
9. What are isotopes?
Answer: Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. They have different mass numbers.
10. How is the atomic number of an element defined?
Answer: The atomic number is the number of protons in the nucleus of an atom. It determines the identity of the element.
11. How is the mass number of an atom calculated?
Answer: The mass number is calculated by adding the number of protons and neutrons in the nucleus.
12. What is the electronic configuration of an atom?
Answer: Electronic configuration is the distribution of electrons in the atomic orbitals. For example, the electronic configuration of carbon is 1s² 2s² 2p².
13. What are energy levels or shells in an atom?
Answer: Energy levels or shells are regions around the nucleus where electrons are likely to be found. Each shell can hold a specific maximum number of electrons.
14. What is the significance of the principal quantum number?
Answer: The principal quantum number (n) indicates the main energy level or shell of an electron. It also determines the size and energy of the orbital.
15. Explain the concept of quantization of energy levels.
Answer: Quantization of energy levels means that electrons can only occupy specific energy levels within an atom, and they can only absorb or emit energy in discrete amounts to move between these levels.
16. What is the role of neutrons in the nucleus?
Answer: Neutrons contribute to the mass of the nucleus and help stabilize it by reducing the repulsive forces between protons.
17. Describe the discovery of the electron.
Answer: The electron was discovered by J.J. Thomson in 1897 through experiments with cathode rays, which showed that atoms contain negatively charged particles.
18. What are valence electrons?
Answer: Valence electrons are the electrons present in the outermost shell of an atom. They are involved in chemical bonding and reactions.
19. What is the difference between an atom and an ion?
Answer: An atom is electrically neutral with equal numbers of protons and electrons. An ion is an atom that has gained or lost electrons, resulting in a net charge.
20. What is the significance of the atomic model?
Answer: The atomic model provides a framework for understanding the structure of atoms and how they interact with each other, which is fundamental for explaining chemical reactions and properties of elements.
These questions cover key concepts related to the structure of the atom and should help in understanding the chapter comprehensively
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