Atomic Structure

16 free MDCAT Chemistry MCQs on Atomic Structure (PM&DC syllabus), each with the answer, an explanation and the textbook line it comes from. Tap to check, no sign-up.

Tap an answer to check it · 16 questions

1. Question 1

   Electrons enter degenerate orbitals singly, with the same spin, before pairing. This is:
   • AMoseley's law
   • BPauli exclusion principle
   • CAufbau principle
   • DHund's rule
   Show answer and explanation

   Answer: D) Hund's rule

   Hund's rule gives the maximum number of unpaired electrons with parallel spins. Source: Chemistry 11 KPK (taleem360.com), p. 68.

2. Question 2

   The charge-to-mass ratio (e/m) of cathode rays is:
   • A1.7588 x 10^11 C/kg
   • B1.7588 x 10^23 C/kg
   • C1.7588 x 10^7 C/kg
   • D1.7588 x 10^-31 C/kg
   Show answer and explanation

   Answer: A) 1.7588 x 10^11 C/kg

   e/m of the electron = 1.7588 x 10^11 C/kg; with e = 1.6022 x 10^-19 C it gives m = 9.11 x 10^-31 kg. Source: Chemistry 11 KPK (taleem360.com), p. 34.

3. Question 3

   The splitting of spectral lines in a magnetic field is called the:
   • AStark effect
   • BZeeman effect
   • CCompton effect
   • DPhotoelectric effect
   Show answer and explanation

   Answer: B) Zeeman effect

   Zeeman effect: magnetic field; Stark effect: electric field. It led to the magnetic quantum number. Source: Chemistry 11 KPK (taleem360.com), p. 61.

4. Question 4

   The maximum number of electrons that the 3s orbital can hold is:
   • ATen
   • BSix
   • CTwo
   • DOne
   Show answer and explanation

   Answer: C) Two

   Any single orbital holds at most two electrons with opposite spins. Source: Chemistry 11 KPK (taleem360.com), p. 63.

5. Question 5

   The energy of the electron in the second orbit (n = 2) of hydrogen is about (E1 = -1312.36 kJ/mol):
   • A-1312 kJ/mol
   • B-656 kJ/mol
   • C-328 kJ/mol
   • D-146 kJ/mol
   Show answer and explanation

   Answer: C) -328 kJ/mol

   E2 = -1312.36 / 2^2 = -328 kJ/mol. Source: Chemistry 11 KPK (taleem360.com), p. 44.

6. Question 6

   As the principal quantum number n increases, the energy of the electron in hydrogen:
   • ABecomes zero
   • BDecreases
   • CStays constant
   • DIncreases
   Show answer and explanation

   Answer: D) Increases

   Energies are negative and become less negative (higher) as n increases. Source: Chemistry 11 KPK (taleem360.com), p. 44.

7. Question 7

   How much energy is released when the electron of a hydrogen atom falls from n = 3 to n = 1?
   • A1166.5 kJ/mol
   • B1312.4 kJ/mol
   • C145.8 kJ/mol
   • D984.3 kJ/mol
   Show answer and explanation

   Answer: A) 1166.5 kJ/mol

   ΔE = 1312.36 (1/1^2 - 1/3^2) = 1312.36 x 8/9 = 1166.5 kJ/mol. Source: Chemistry 11 KPK (taleem360.com), p. 45.

8. Question 8

   A radiation has a wave number of 0.5 x 10^8 m^-1. Its frequency (c = 3 x 10^8 m/s) is:
   • A6.0 x 10^15 Hz
   • B1.5 x 10^16 Hz
   • C3.0 x 10^16 Hz
   • D0.6 x 10^-1 Hz
   Show answer and explanation

   Answer: B) 1.5 x 10^16 Hz

   v = c x wave number = 3 x 10^8 x 0.5 x 10^8 = 1.5 x 10^16 Hz. Source: Chemistry 11 KPK (taleem360.com), p. 54.

9. Question 9

   A K-alpha (Kα) characteristic X-ray photon is emitted when an electron moves from the:
   • AM shell to K shell
   • BN shell to L shell
   • CK shell to L shell
   • DL shell to K shell
   Show answer and explanation

   Answer: D) L shell to K shell

   Kα: L to K; Kβ: M to K; Kγ: N to K. Source: Chemistry 11 KPK (taleem360.com), p. 56.

10. Question 10

    Following Moseley's work, the atomic number of an element is defined as the number of:
    • AProtons in its nucleus
    • BNeutrons in its nucleus
    • CNucleons in its nucleus
    • DElectrons in its outer shell
    Show answer and explanation

    Answer: A) Protons in its nucleus

    The positive nuclear charge comes from protons. Source: Chemistry 11 KPK (taleem360.com), p. 57.

11. Question 11

    The principal quantum number (n) describes the:
    • AShape of the orbital
    • BMain energy level (shell)
    • COrientation of the orbital
    • DDirection of spin
    Show answer and explanation

    Answer: B) Main energy level (shell)

    n: shell; l: shape (sub-shell); m: orientation; s: spin. Source: Chemistry 11 KPK (taleem360.com), p. 60.

12. Question 12

    The azimuthal quantum number (l) describes the:
    • AOrientation in space
    • BSize of the shell
    • CShape of the orbital
    • DDirection of spin
    Show answer and explanation

    Answer: C) Shape of the orbital

    l = 0, 1, 2, 3 for s, p, d, f sub-shells, each with its own shape. Source: Chemistry 11 KPK (taleem360.com), p. 60.

13. Question 13

    For l = 2 (a d sub-shell), how many values of the magnetic quantum number m are possible?
    • A2
    • B3
    • C7
    • D5
    Show answer and explanation

    Answer: D) 5

    m runs from -l to +l: 2l + 1 = 5 values, i.e. five d orbitals. Source: Chemistry 11 KPK (taleem360.com), p. 61.

14. Question 14

    For n = 3, the possible values of the azimuthal quantum number l are:
    • A0, 1 and 2
    • B1, 2 and 3
    • C0, 1, 2 and 3
    • D1 and 2
    Show answer and explanation

    Answer: A) 0, 1 and 2

    l runs from 0 to n - 1: 0, 1, 2 (3s, 3p, 3d). Source: Chemistry 11 KPK (taleem360.com), p. 61.

15. Question 15

    The maximum number of electrons that the M shell (n = 3) can hold is:
    • A8
    • B18
    • C9
    • D32
    Show answer and explanation

    Answer: B) 18

    Maximum = 2n^2 = 2 x 3^2 = 18. Source: Chemistry 11 KPK (taleem360.com), p. 60.

16. Question 16

    In the most stable arrangement of carbon (1s2 2s2 2p2), the two 2p electrons are:
    • APaired in one orbital
    • BUnpaired, with opposite spins
    • CUnpaired, with the same spin
    • DBoth in the 2s orbital
    Show answer and explanation

    Answer: C) Unpaired, with the same spin

    Hund's rule: separate degenerate orbitals with parallel spins give maximum stability. Source: Chemistry 11 KPK (taleem360.com), p. 68.

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