NCERT Solutions for Class 11 Chemistry Chapter 2

NCERT Solutions for Class 11 Chemistry Chapter 2 – Structure of Atom are available here as a free learning resource for Class 11 students. These solutions provide detailed answers to all questions in Chapter 2 of the NCERT Chemistry textbook, ensuring a clear understanding of the structure of an atom. The primary goal of these NCERT Solutions is to help students focus on key concepts and learn them effectively.

Numerical problems in this chapter can be challenging, especially for board exam preparation. To make learning easier, Infinity Learn faculty have prepared step-by-step solutions aligned with the CBSE Class 11 Chemistry Syllabus 2025–26 and the marks distribution. Each solution includes clear explanations to support better concept retention and problem-solving skills.

Students can also download the NCERT Solutions for Class 11 Chemistry Chapter 2 PDF for free by clicking the download button below and use it for convenient offline study.

NCERT Solutions Class 11 Chemistry Chapter 2 - Questions with Answers

Q1. What are the main postulates of Dalton’s Atomic Theory?

Answer:

1. Matter is made up of indivisible particles called atoms.

Q2. Define atomic number and mass number.

Answer:

• Atomic Number (Z): Number of protons present in the nucleus of an atom.

Q3. Write the electronic configuration of chlorine (Z = 17).

Answer:
Cl: 1s² 2s² 2p⁶ 3s² 3p⁵
or simply 2, 8, 7

Q4. What are isotopes? Give an example.

Answer:
Isotopes are atoms of the same element having the same atomic number but different mass numbers.
Example: ¹H, ²H (Deuterium), and ³H (Tritium).

Q5. What is the difference between orbit and orbital?

Answer:

• Orbit: Fixed circular path around the nucleus in which electrons revolve (Bohr’s model).

Q6. Calculate the number of protons, neutrons, and electrons in ¹⁷Cl³⁷.

Answer:

• Atomic number (Z) = 17 → Protons = 17, Electrons = 17

Q7. State Hund’s Rule of maximum multiplicity.

Answer:
Hund’s Rule states that electrons fill degenerate orbitals (same energy) singly first, with parallel spins, before pairing occurs.

Q8. Calculate the wavelength of light emitted when an electron in a hydrogen atom transition from n = 3 to n = 2.

Answer:
Using Rydberg equation:
$\dfrac{1}{\lambda} = R_H \left( \dfrac{1}{n_1^2} - \dfrac{1}{n_2^2} \right)$
Here, $n_1 = 2$, $n_2 = 3$, $R_H = 1.097 × 10^7 \, m^{-1}$
$\dfrac{1}{\lambda} = 1.097 × 10^7 \left( \dfrac{1}{2^2} - \dfrac{1}{3^2} \right)$
= $1.097 × 10^7 (0.25 – 0.111)$
= $1.097 × 10^7 (0.139)$
= $1.52 × 10^6 \, m^{-1}$
$\lambda = 6.56 × 10^{-7} m = 656 \, nm$
This corresponds to the red line of the Balmer series.

Q9. What is Heisenberg’s Uncertainty Principle?

Answer:
It states that it is impossible to determine simultaneously and precisely both the position and momentum of an electron.
Mathematically:
$\Delta x \cdot \Delta p ≥ \dfrac{h}{4π}$

Q10. Write the four quantum numbers for the valence electron of sodium (Na, Z = 11).

Answer:
Valence electron of Na = 3s¹

• Principal quantum number (n) = 3

Q11. What is meant by electromagnetic radiation?

Answer:
Electromagnetic radiation is a form of energy that exhibits both wave-like and particle-like properties. It is characterized by wavelength (λ), frequency (ν), and velocity (c). Examples: visible light, X-rays, microwaves.

Q12. Write Planck’s Quantum Theory in brief.

Answer:

1. Energy is emitted or absorbed in discrete packets called quanta.

Q13. What is the difference between continuous spectrum and line spectrum?

Answer:

• Continuous spectrum: Contains all wavelengths without gaps (e.g., sunlight).

Q14. Calculate the energy of a photon of light with wavelength 400 nm. (h = 6.626×10⁻³⁴ J·s, c = 3×10⁸ m/s).

Answer:
$E = \dfrac{hc}{λ}$
= $\dfrac{6.626×10⁻³⁴ × 3×10⁸}{400×10⁻⁹}$
= $4.97×10⁻¹⁹ J$ per photon.

Q15. State Pauli’s Exclusion Principle.

Answer:
No two electrons in an atom can have the same set of four quantum numbers. An orbital can hold a maximum of two electrons with opposite spins.

Q16. Give one limitation of Bohr’s model of an atom.

Answer:
It could not explain spectra of multi-electron atoms or fine structures observed in hydrogen spectrum.

Q17. What are degenerate orbitals? Give an example.

Answer:
Orbitals having the same energy are called degenerate orbitals.
Example: 2px, 2py, and 2pz orbitals

Q18. Which quantum number distinguishes orbitals of different shapes?

Answer:
The azimuthal quantum number (l) defines the shape of orbitals:

• l = 0 (s-spherical)

Q19. Calculate the number of electrons that can be accommodated in the nth shell.

Answer:
Maximum electrons in nth shell = 2n².
Example: For n = 3 → 2(3²) = 18 electrons.

Q20. What are isobars? Give an example.

Answer:
Isobars are atoms of different elements with the same mass number but different atomic numbers.
Example: ⁴⁰Ca (Z = 20) and ⁴⁰Ar (Z = 18).

21. What is photoelectric effect?

Answer:
When light of suitable frequency strikes a metal surface, electrons are ejected. This phenomenon is called the photoelectric effect. It supports the particle nature of light.

Q22. State the mathematical expression for de Broglie wavelength.

Answer:
$\lambda = \dfrac{h}{mv}$
where λ = wavelength, h = Planck’s constant, m = mass, v = velocity of particle.

Q23. Calculate the de Broglie wavelength of an electron moving with velocity 2.2 × 10⁶ m/s. (h = 6.626×10⁻³⁴ J·s, m = 9.1×10⁻³¹ kg)

Answer:
$\lambda = \dfrac{h}{mv}$
= $\dfrac{6.626×10⁻³⁴}{9.1×10⁻³¹ × 2.2×10⁶}$
= $3.3 × 10⁻¹⁰ m$.

Q24. What is the principal quantum number?

Answer:
The quantum number ‘n’ represents the main energy level or shell of an electron. It determines the size and energy of orbitals.

Q25. Explain Aufbau principle with an example.

Answer:
Electrons are filled in orbitals in order of increasing energy (given by n+l rule).
Example: After 1s, electrons enter 2s, then 2p, then 3s, etc.

Q26. What are cathode rays? Mention two properties.

Answer:
Cathode rays are streams of negatively charged particles (electrons) emitted from the cathode in a discharge tube.
Properties:

1. Travel in straight lines.

Q27. Write the drawbacks of Rutherford’s model of atom.

Answer:

1. Failed to explain stability of atom (accelerating electrons should emit energy and collapse).

Q28. Which series of hydrogen spectrum lies in the visible region?

Answer:
The Balmer series (n₁ = 2, n₂ = 3,4,5 …) lies in the visible region.

Q29. Write the shapes of s, p, and d orbitals.

Answer:

• s-orbital: spherical

Q30. Define shielding effect.

Answer:
The reduction in effective nuclear charge on the outer electrons due to repulsion from inner-shell electrons is called shielding or screening effect.