Journey Inside the Atom — Class 9 Science NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 9 Science chapter "Journey Inside the Atom" — 8 important questions with detailed answers for CBSE board exam preparation.

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TL;DR: Free step-by-step NCERT solutions for Class 9 Science chapter "Journey Inside the Atom" — 8 important questions with detailed answers for CBSE board e…

Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated Jul 23, 2026

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Key Questions Covered:

What are the three subatomic particles and their charges?
State and explain Thomson's model of atom.
What are the main features of Rutherford's model of atom?
Explain Bohr's model of atom. Why is it better than Rutherford's?
Define atomic number and mass number. How are they related?
What is valency? How does electron configuration determine valency?
+ 2 more questions in the full chapter

Solutions Summary:

Question	Status
What are the three subatomic particles and their charges?	✓ Solved
State and explain Thomson's model of atom.	✓ Solved
What are the main features of Rutherford's model of atom?	✓ Solved
Explain Bohr's model of atom. Why is it better than Ruthe…	✓ Solved
Define atomic number and mass number. How are they related?	✓ Solved
What is valency? How does electron configuration determin…	✓ Solved

Showing 6 of 8 questions

Q1: What are the three subatomic particles and their charges?

The three subatomic particles are: (1) Electron — negatively charged (charge = -1), mass = 1/1836 amu, found in orbitals around nucleus (2) Proton — positively charged (charge = +1), mass = 1 amu, present in nucleus (3) Neutron — neutral (charge = 0), mass ≈ 1 amu, present in nucleus

Q2: State and explain Thomson's model of atom.

Thomson's model (plum pudding model): Atom is a sphere of positive charge with electrons embedded in it like raisins in a pudding. Characteristics: (1) Positive charge uniformly distributed throughout atom (2) Electrons scattered throughout in this positive charge (3) Atom is electrically neutral Limitations: Could not explain scattering of α-particles; disproved by Rutherford's experiments.

Q3: What are the main features of Rutherford's model of atom?

Rutherford's nuclear model: (1) Atom has a small, dense, positively charged nucleus at center (2) Electrons revolve around nucleus in circular paths (3) Most of atom's mass is concentrated in nucleus (4) Nucleus contains protons; electrons in orbits (5) Atom is mostly empty space Limitation: Could not explain stability of electrons; they should spiral into nucleus.

Q4: Explain Bohr's model of atom. Why is it better than Rutherford's?

Bohr's model: (1) Electrons exist in fixed orbits/shells (n = 1, 2, 3...) at specific distances from nucleus (2) Electrons in a shell have definite energy; transition between shells requires energy (3) Orbits are labeled K, L, M, N (n = 1, 2, 3, 4...) (4) Maximum electrons in shell = 2n² Advantages over Rutherford: (1) Explains why electrons don't spiral into nucleus (2) Explains discrete energy levels and spectral lines (3) Applies to hydrogen and hydrogen-like atoms

Q5: Define atomic number and mass number. How are they related?

Atomic number (Z) = Number of protons in nucleus = Number of electrons in neutral atom Mass number (A) = Total number of protons + neutrons = Z + N where N = number of neutrons Example: ₁₆³²S has Z = 16 (16 protons), A = 32, so N = 32 - 16 = 16 neutrons Atomic number determines element identity; mass number determines isotope.

Q6: What is valency? How does electron configuration determine valency?

Valency = Number of electrons lost, gained, or shared by atom to achieve stable octet (8 electrons in outermost shell) or duplet (2 electrons for H, He). Rules: (1) If valence electrons < 4: valency = number of valence electrons (2) If valence electrons ≥ 4: valency = 8 - number of valence electrons Example: Chlor (17e⁻): 2, 8, 7 → 7 valence electrons → valency = 8 - 7 = 1 Oxygen (8e⁻): 2, 6 → 6 valence electrons → valency = 8 - 6 = 2

Showing 6 of 8 questions. Visit the full page for complete solutions.