8th Class Chemistry Atomic Structure Important Exam Questions with Answers
Atomic structure is a fundamental topic in chemistry that helps students understand atoms, elements, and their composition. Below are some important exam questions with answers to help 8th-grade students prepare effectively.
1. Define an atom.
Answer: An atom is the smallest unit of an element that retains its chemical properties. It consists of a nucleus containing protons and neutrons, surrounded by electrons in orbitals.
2. What are the three subatomic particles of an atom?
Answer: The three subatomic particles are:
- Protons (positively charged, found in the nucleus)
- Neutrons (neutral charge, found in the nucleus)
- Electrons (negatively charged, orbit around the nucleus)
3. What is the charge of an electron, proton, and neutron?
Answer:
- Electron: -1 (negative charge)
- Proton: +1 (positive charge)
- Neutron: 0 (neutral charge)
4. Define atomic number and mass number.
Answer:
- Atomic Number (Z): The number of protons in an atom’s nucleus.
- Mass Number (A): The total number of protons and neutrons in an atom’s nucleus.
Formula: Mass Number = Protons + Neutrons
5. What is an isotope? Give an example.
Answer: Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
Example: Carbon has three isotopes – Carbon-12, Carbon-13, and Carbon-14.
6. What is an ion? Differentiate between cation and anion.
Answer:
- Ion: An atom or molecule with an electric charge due to the loss or gain of electrons.
- Cation: A positively charged ion (formed by losing electrons). Example: Na⁺
- Anion: A negatively charged ion (formed by gaining electrons). Example: Cl⁻
7. What is the Bohr model of an atom?
Answer: The Bohr model describes an atom as having electrons moving in fixed orbits around the nucleus. The energy levels are quantized, meaning electrons can only exist in certain allowed orbits.
8. Explain the structure of the nucleus.
Answer: The nucleus is the central part of an atom, containing protons and neutrons. It is responsible for most of the atom’s mass and is held together by strong nuclear forces.
9. What is electronic configuration? Give an example.
Answer: Electronic configuration is the arrangement of electrons in an atom’s orbitals.
Example: Oxygen (Atomic number = 8) has an electronic configuration of 2, 6 (2 electrons in the first shell, 6 in the second shell).
10. What is the valency of an element? How is it determined?
Answer: Valency is the combining capacity of an atom. It is determined by the number of electrons an atom gains, loses, or shares to achieve a stable configuration.
Example: Sodium (Na) has 1 valency, while Oxygen (O) has 2 valency.
Conclusion
Understanding atomic structure is crucial for mastering chemistry concepts. These important questions will help 8th-class students grasp the topic effectively and prepare for exams with confidence.
Author: Hari Babu Dondapati
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