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.
Q: What are isobars?
A: Isobars are atoms of different elements with different atomic numbers but the same mass number.
Q: Who discovered the neutron?
A: J. Chadwick discovered the neutron in 1932.
Q: Why are noble gases chemically inert?
A: Noble gases have completely filled outermost shells (8 electrons), making them highly stable and unreactive.
Q: How is the average atomic mass of an element calculated?
A: By considering the percentage of each isotope and calculating the weighted average of their masses.
Q: What are some practical applications of isotopes?
A: (i) Uranium isotope used as fuel in nuclear reactors
(ii) Cobalt isotope used in cancer treatment
(iii) Iodine isotope used in treating goitre
Q: What was a major limitation of Rutherford’s atomic model?
A: The model could not explain why electrons do not lose energy and fall into the nucleus, which would make atoms unstable.
Q: How do atoms achieve stability?
A: By gaining, losing, or sharing electrons to achieve a full octet (8 electrons) in the outermost shell.
Q: How is an atom’s electronic configuration represented?
A: By writing the number of electrons in each shell, starting from the innermost shell (K), such as 2,8,1 for sodium.
Q: How does the number of electrons relate to the atom’s charge?
A: When the number of electrons equals the number of protons, the atom is neutral. If electrons are gained or lost, the atom becomes an ion with a negative or positive charge.
Class 9 Science The Fundamentals of Life Extra Question Answer
