Structure of Atom

What you'll learn

A from-scratch guide to the atom for CBSE Class 11 Science: the three sub-atomic particles, atomic and mass number, the Bohr model with a worked numerical, the four quantum numbers, orbitals, and the Aufbau, Pauli and Hund rules for electronic configuration - with the Cr and Cu exceptions.

This chapter has

Structure of Atom — solved practice questions

8 Class 11 Chemistry questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   The subatomic particle carrying a negative charge and having negligible mass is the:

   • Aproton
   • Bneutron
   • Celectron
   • Dpositron
   Show answer & solution

   Correct answer: (C) electron

   The electron carries a charge of -1.6 x 10^-19 C and has a mass about 1/1836 that of a proton, which is negligible.

2. Q2easy

   Rutherford's alpha-particle scattering (gold foil) experiment established the existence of the:

   • Anucleus
   • Belectron
   • Cneutron
   • Dproton
   Show answer & solution

   Correct answer: (A) nucleus

   The deflection and back-scattering of a few alpha particles led Rutherford to conclude that the atom has a small, dense, positively charged nucleus.

3. Q3easy

   The maximum number of electrons that can be accommodated in a shell with principal quantum number n is:

   • An^2
   • B2n^2
   • Cn + 1
   • D2n
   Show answer & solution

   Correct answer: (B) 2n^2

   The capacity of a shell is given by the formula 2n^2, e.g. for n = 3 it is 2 x 9 = 18 electrons.

4. Q4medium

   The quantum number that determines the shape of an orbital is the:

   • Aprincipal quantum number (n)
   • Bmagnetic quantum number (m_l)
   • Cspin quantum number (m_s)
   • Dazimuthal quantum number (l)
   Show answer & solution

   Correct answer: (D) azimuthal quantum number (l)

   The azimuthal (angular momentum) quantum number l determines the shape of the orbital (s, p, d, f), while n gives size and m_l gives orientation.

5. Q5easy

   The number of orbitals present in the d-subshell is:

   • A1
   • B3
   • C5
   • D7
   Show answer & solution

   Correct answer: (C) 5

   The d-subshell has l = 2, giving m_l values -2, -1, 0, +1, +2, which corresponds to 5 orbitals.

6. Q6medium

   The correct ground-state electronic configuration of sodium (Z = 11) is:

   • A1s2 2s2 2p6 3s1
   • B1s2 2s2 2p6
   • C1s2 2s2 2p6 3s2 3p1
   • D1s2 2s2 2p5 3s2
   Show answer & solution

   Correct answer: (A) 1s2 2s2 2p6 3s1

   Filling 11 electrons following the Aufbau principle gives 1s2 2s2 2p6 3s1.

7. Q7medium

   The number of unpaired electrons in a nitrogen atom (Z = 7) is:

   • A0
   • B1
   • C2
   • D3
   Show answer & solution

   Correct answer: (D) 3

   Nitrogen is 1s2 2s2 2p3; by Hund's rule the three 2p electrons occupy separate orbitals singly, giving 3 unpaired electrons.

8. Q8medium

   According to the Aufbau principle, which of these orbitals is filled first?

   • A3d
   • B4s
   • C4p
   • D4d
   Show answer & solution

   Correct answer: (B) 4s

   By the (n + l) rule, 4s has n + l = 4 while 3d has n + l = 5, so the 4s orbital is filled before 3d.

Want the full set? Practise all 15 Structure of Atom questions →