Class 9 Science Structure of the Atom
Learn about the Class 9 Science Structure of the Atom in . Understand the basic concepts, parts of an atom, and how it makes up everything around us!”
Q: What are the three sub-atomic particles of an atom?
A: Electrons (negatively charged), protons (positively charged), and neutrons (no charge).
Q: Who discovered the electron and proton?
A: J.J. Thomson discovered the electron, and E. Goldstein discovered the proton.
Q: What was J.J. Thomson’s model of the atom?
A: Thomson proposed the “plum pudding” model, where electrons were embedded in a positively charged sphere, like currants in a pudding.
Q: What were the key findings of Rutherford’s gold foil experiment?
A: Most alpha particles passed straight through, some were deflected, and a few were completely bounced back, leading to the discovery of the atomic nucleus.
Q: What are the main features of Rutherford’s atomic model?
A: (i) A positively charged nucleus at the center, (ii) Electrons revolving around the nucleus, (iii) Most of the atom’s mass is in the nucleus, which is very small compared to the atom’s size.
Q: What are the main postulates of Bohr’s atomic model?
A: (i) Electrons move in discrete orbits, (ii) Electrons do not radiate energy while revolving in these orbits.
Q: How are electrons distributed in different shells?
A: According to the Bohr-Bury scheme:
- Maximum electrons in a shell = 2n²
- First shell (K) can hold 2 electrons
- Second shell (L) can hold 8 electrons
- Third shell (M) can hold 18 electrons
- Shells are filled step by step
Q: What is valency?
A: Valency is the combining capacity of an atom, determined by the number of electrons in the outermost shell that are gained, lost, or shared to achieve a full octet (8 electrons).
Q: What is atomic number?
A: Atomic number is the total number of protons in the nucleus of an atom, represented by Z. It defines the element.
Q: What is mass number?
A: Mass number is the sum of the number of protons and neutrons in the nucleus of an atom, represented by A.
Q: What are isotopes?
A: Isotopes are atoms of the same element with the same atomic number but different mass numbers due to a different number of neutrons.
