NCERT Solutions Class 11 chemistry Chapter 2 Structure of atom

NCERT Solutions for Class 11 Chemistry Chapter 2 Structure of Atom are provided here as a free and reliable study resource for students. These solutions offer clear and detailed answers to all the questions from Chapter 2 of the NCERT textbook, helping students understand the concept of atomic structure effectively. The main goal is to simplify important topics and strengthen conceptual clarity.

Many students find numerical problems challenging in exams. To address this, the NCERT solutions are designed in a step-by-step manner, making it easier to understand and solve questions based on CBSE guidelines. Each step is explained clearly to enhance learning. Students can also download the NCERT Solutions for Class 11 Chemistry Chapter 2 PDF for free and study anytime.

NCERT Solutions Class 11 Chemistry Chapter 2 – Free PDF Download

Structure of Atom Class 11 questions and answers help students clearly understand the composition of atoms, including electrons, protons, and neutrons. Class 11 Chemistry Chapter 3 NCERT Solutions and Chapter 2 resources simplify these concepts, making them easier to grasp.

Infinity Learn provides clear and easy-to-follow solutions for every question in this chapter. Each answer is explained step by step to improve understanding and accuracy. These solutions help students practice different types of questions with confidence. You can also access the Structure of Atom Class 11 NCERT Solutions PDF Download for free and strengthen your understanding of atomic structure.

NCERT Solutions for Class 11 Chemistry Chapter 2 Structure of Atom

Structure of Atom is the second chapter in the NCERT Class 11 Chemistry textbook. This chapter helps students understand how atoms are formed and how their internal structure works.

Topics Covered in This Chapter

This chapter includes important concepts such as:

• Subatomic particles (electrons, protons, neutrons)
• Thomson’s atomic model
• Rutherford’s atomic model
• Bohr’s atomic model
• Quantum mechanical model of the atom

Types of Questions You’ll Practice

In this chapter, students come across a variety of questions, including:

• Basic calculations related to subatomic particles
• Numericals based on wavelength and frequency
• Problems involving energy of electromagnetic radiation
• Questions on electron transitions between shells
• Writing electron configurations
• Questions based on quantum numbers and their combinations

Access the answers of NCERT Solutions for Class 11 Chemistry Chapter 2

1. (i) Calculate the number of electrons which will together weigh one gram.

Ans: Mass of one electron = 9.10939 × 10⁻³¹ kg

Number of electrons that will weigh 1 g =

(1 × 10⁻³) / (9.10939 × 10⁻³¹) = 1.098 × 10²⁷

(ii) Calculate the mass and charge of one mole of electrons.

Ans: Mass of one electron = 9.10939 × 10⁻³¹ kg

Mass of one mole of electrons =

(6.022 × 10²³) × (9.10939 × 10⁻³¹) = 5.48 × 10⁻⁷ kg

Charge on one electron = 1.6022 × 10⁻¹⁹ C

Charge on one mole of electrons =

(1.6022 × 10⁻¹⁹) × (6.022 × 10²³) = 9.65 × 10⁴ C

2. (i) Calculate the total number of electrons present in one mole of methane.

Ans: Electrons in one molecule of CH₄ =

1(6) + 4(1) = 10

Electrons in one mole =

6.023 × 10²³ × 10 = 6.023 × 10²⁴

(ii) (a) Find total number of neutrons in 7 mg of ¹⁴C.

Ans: Neutrons per atom = 14 − 6 = 8

Total neutrons =

(6.022 × 10²³ × 8 × 7) / 1400 = 2.4092 × 10²¹

(b) Total mass of neutrons

Ans: Mass =

(2.4092 × 10²¹) × (1.67493 × 10⁻²⁷) = 4.0352 × 10⁻⁶ kg

3. How many electrons, protons and neutrons are present in the following atoms/ions?

(i) ¹⁶O

(ii) ²⁷Al³⁺

(iii) ³⁵Cl⁻

(iv) ⁴⁰Ca²⁺

Ans:

(i) ¹⁶O

Atomic number = 8

Number of electrons = 8

Number of protons = 8

Number of neutrons = 16 − 8 = 8

(ii) ²⁷Al³⁺

Atomic number = 13

Number of protons = 13

Number of electrons = 13 − 3 = 10

Number of neutrons = 27 − 13 = 14

(iii) ³⁵Cl⁻

Atomic number = 17

Number of protons = 17

Number of electrons = 17 + 1 = 18

Number of neutrons = 35 − 17 = 18

(iv) ⁴⁰Ca²⁺

Atomic number = 20

Number of protons = 20

Number of electrons = 20 − 2 = 18

Number of neutrons = 40 − 20 = 20

4. (i) Calculate the wavelength of an electron moving with a velocity of 2.05 × 10⁷ m s⁻¹.

Ans: Using de Broglie equation:

λ = h / mv

h = 6.626 × 10⁻³⁴ Js

m = 9.1 × 10⁻³¹ kg

v = 2.05 × 10⁷ m/s

λ = (6.626 × 10⁻³⁴) / (9.1 × 10⁻³¹ × 2.05 × 10⁷)

λ = 3.55 × 10⁻¹¹ m

(ii) Calculate the velocity of an electron having de Broglie wavelength of 1 Å.

Ans:

λ = 1 Å = 1 × 10⁻¹⁰ m

v = h / mλ

v = (6.626 × 10⁻³⁴) / (9.1 × 10⁻³¹ × 1 × 10⁻¹⁰)

v = 7.28 × 10⁶ m/s

5. (i) Calculate the energy of a photon whose wavelength is 300 nm.

Ans: Using formula:

E = hc / λ

h = 6.626 × 10⁻³⁴ Js

c = 3 × 10⁸ m/s

λ = 300 nm = 300 × 10⁻⁹ m

E = (6.626 × 10⁻³⁴ × 3 × 10⁸) / (300 × 10⁻⁹)

E = 6.626 × 10⁻¹⁹ J

(ii) What is the frequency of the radiation?

Ans: ν = c / λ

ν = (3 × 10⁸) / (300 × 10⁻⁹)

ν = 1 × 10¹⁵ s⁻¹

6. Calculate the number of photons emitted per second by a source of power 100 W and wavelength 600 nm.

Ans: Energy of one photon:

E = hc / λ

E = (6.626 × 10⁻³⁴ × 3 × 10⁸) / (600 × 10⁻⁹)

E = 3.313 × 10⁻¹⁹ J

Number of photons per second =

Power / Energy per photon = 100 / (3.313 × 10⁻¹⁹)

= 3.02 × 10²⁰ photons/s

7. Calculate the wavelength of a photon emitted when an electron in hydrogen atom jumps from n = 3 to n = 2.

Ans: Using Rydberg formula:

1/λ = R (1/n₁² − 1/n₂²)

R = 1.097 × 10⁷ m⁻¹

1/λ = 1.097 × 10⁷ (1/2² − 1/3²)

1/λ = 1.097 × 10⁷ (1/4 − 1/9)

1/λ = 1.097 × 10⁷ × (5/36)

λ = 656 nm

8. a) Find the total number of neutrons in 7mg of ¹⁴C. (Assume the mass of a neutron = 1.675 × 10⁻²⁷ kg)

Ans: Number of atoms of ¹⁴C in 1 mole = 6.023 × 10²³
Since 1 atom of ¹⁴C contains (14−6) i.e., 8 neutrons, the number of neutrons in 14g of ¹⁴C is:

(6.023 × 10²³) × 8

Number of neutrons in 7 mg =

(6.022 × 10²³ × 8 × 7) / 1400

= 2.4092 × 10²¹

(b) Find the total mass of neutrons in 7mg of ¹⁴C.

Ans: Mass of one neutron = 1.67493 × 10⁻²⁷ kg

Mass of total neutrons =

(2.4092 × 10²¹) × (1.67493 × 10⁻²⁷)

= 4.0352 × 10⁻⁶ kg

(iii) a) Find the total number of protons in 34mg of NH₃ at STP.

Ans: 1 mole of NH₃ = 17 g
Number of molecules = 6.023 × 10²³

Number of protons in one molecule of NH₃ =

{1(7) + 1(3)} = 10

Total protons in 1 mole =

(6.023 × 10²³) × 10 = 6.023 × 10²⁴

Number of protons in 34 mg =

(6.022 × 10²⁴ × 34) / 1700

= 1.2046 × 10²²

(b) Find the total mass of protons in 34mg of NH₃.

Ans: Mass of one proton = 1.67493 × 10⁻²⁷ kg

Total mass of protons =

(1.2046 × 10²²) × (1.67493 × 10⁻²⁷)

= 2.0176 × 10⁻⁵ kg

The number of protons, electrons, and neutrons in an atom is independent of temperature and pressure. Hence, values remain unchanged.

Class 11 NCERT solutions Chapter 2 Important Formulas and Concepts

Here are the important formulas and key concepts from Class 11 Chemistry Chapter 2 – Structure of Atom, extracted and organized in a simple, revision-friendly format based on your PDF content :

Important Formulas – Structure of Atom

1. Number of Particles

• Number of electrons (neutral atom) = Atomic number (Z)
• Number of protons = Atomic number (Z)
• Number of neutrons = Mass number (A) − Atomic number (Z)

2. Energy of Photon

• E = hν
• E = hc / λ

Where:

• h = Planck’s constant (6.626 × 10⁻³⁴ Js)
• ν = frequency
• λ = wavelength
• c = speed of light (3 × 10⁸ m/s)

3. Relationship Between Frequency & Wavelength

• c = νλ
• ν = c / λ

4. Wave Number

• ṽ = 1 / λ

5. Rydberg Formula (Hydrogen Spectrum)

• 1/λ = R (1/n₁² − 1/n₂²)

Where:

• R = 1.097 × 10⁷ m⁻¹

6. Bohr’s Energy Equation

• Eₙ = −2.18 × 10⁻¹⁸ Z² / n² (J)

7. Bohr Radius

• rₙ = 0.529 × n² / Z (Å)

8. Maximum Spectral Lines

• n(n − 1) / 2

9. de Broglie Equation

• λ = h / mv

10. Kinetic Energy

• K.E = ½ mv²

11. Heisenberg Uncertainty Principle

• Δx × Δp ≥ h / 4π

12. Charge of Electron

• 1 electron = 1.602 × 10⁻¹⁹ C

Important Concepts

1. Atomic Models

• Thomson model (plum pudding)
• Rutherford model (nucleus discovery)
• Bohr model (quantized orbits)
• Quantum mechanical model

2. Subatomic Particles

• Electron (negative charge)
• Proton (positive charge)
• Neutron (no charge)

3. Quantum Numbers

• n (Principal) - energy level
• l (Azimuthal) - shape of orbital
• m (Magnetic) - orientation
• s (Spin) - electron spin

4. Orbitals

• s, p, d, f types
• Maximum electrons = 2n²

5. Electronic Configuration

• Aufbau principle
• Hund’s rule
• Pauli exclusion principle

6. Isoelectronic Species

• Same number of electrons
• Example: Na⁺, Mg²⁺

7. Electromagnetic Radiation

• Light behaves as both wave and particle
• Includes X-rays, UV, visible light

8. Photoelectric Effect

• Emission of electrons when light hits metal
• Depends on frequency, not intensity

Important Links for CBSE Class 11 Chemistry