Class 11 Chemistry Worksheet on Chapter 2 Structure of Atom Set - 3 - Free Printable

Here's the detailed solution and explanation for each question in the worksheet:

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**Q1. What is the maximum number of orbitals that can be identified with the following quantum numbers?
n = 3, l = 1, mₗ = 0**

✔ Correct Answer: a.) 1

Explanation:
The set of quantum numbers (n, l, mₗ) uniquely identifies one specific orbital.

- n = 3 → third energy level
- l = 1 → p subshell (since l=0→s, l=1→p, l=2→d, etc.)
- mₗ = 0 → specifies the orientation of the orbital; for p subshell (l=1), mₗ can be -1, 0, +1 → three orbitals: pₓ, pᵧ, p_z

But here, mₗ is fixed at 0, so it refers to only one orbital — the p_z orbital (by convention).

So, only one orbital is identified by this exact set.

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Q2. The total number of atomic orbitals in the fourth energy level of an atom is ___

✔ Correct Answer: b.) 16

Explanation:
The number of orbitals in a given energy level (n) is given by n².

For n = 4:
→ Number of orbitals = 4² = 16

Breakdown:
- l = 0 (s subshell) → 1 orbital
- l = 1 (p subshell) → 3 orbitals
- l = 2 (d subshell) → 5 orbitals
- l = 3 (f subshell) → 7 orbitals
Total = 1 + 3 + 5 + 7 = 16 orbitals

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Q3. The magnetic quantum number for the valence electron of potassium is:

✔ Correct Answer: a.) 0

Explanation:
Potassium (K) has atomic number 19. Its electron configuration is:

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

→ Valence electron is in the 4s orbital.

For s orbital:
- l = 0
- mₗ can only be 0 (since mₗ ranges from -l to +l → only 0)

So, magnetic quantum number mₗ = 0

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Q4. Two electrons occupying the same orbital are distinguished by:

✔ Correct Answer: a.) Spin quantum number

Explanation:
According to the Pauli Exclusion Principle, no two electrons in an atom can have the same set of all four quantum numbers.

If two electrons are in the same orbital, they must have the same:
- n (principal)
- l (azimuthal)
- mₗ (magnetic)

They differ only in their spin quantum number (mₛ), which can be either +½ or -½.

Thus, they are distinguished by their spin.

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Q5. Which of the following transitions will have minimum wavelength?

✔ Correct Answer: d.) n₄ → n₁

Explanation:
Wavelength (λ) is inversely proportional to energy difference (ΔE):

> E ∝ 1/λ

So, minimum wavelength corresponds to maximum energy transition.

Energy difference between levels increases as the gap between initial and final levels increases.

Transitions to n₁ (ground state) release more energy than transitions to higher levels.

Among the options:

- a) n₂ → n₁ → moderate energy
- b) n₃ → n₁ → higher energy
- c) n₄ → n₂ → less energy (smaller gap)
- d) n₄ → n₁ → largest energy gap → highest energy → shortest wavelength

✔️ So, n₄ → n₁ has the minimum wavelength.

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Q6. Define the shielding effect.

✔ Answer:

Shielding effect (also called screening effect) is the phenomenon where inner-shell electrons reduce the effective nuclear charge experienced by outer-shell electrons.

In multi-electron atoms, electrons in inner shells “shield” or “screen” the outer electrons from the full attractive force of the nucleus. As a result, the outer electrons feel a reduced positive charge — called the effective nuclear charge (Zₑff).

> Zₑff = Z - σ
Where Z = actual nuclear charge, σ = shielding constant

This effect explains trends like atomic size increase down a group and ionization energy decrease down a group.

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✔ Final Answers Summary:

| Q# | Answer |
|----|--------|
| Q1 | a) 1 |
| Q2 | b) 16 |
| Q3 | a) 0 |
| Q4 | a) Spin quantum number |
| Q5 | d) n₄ → n₁ |
| Q6 | Shielding effect is the reduction in effective nuclear charge on outer electrons due to repulsion by inner electrons. |

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