Bohr’s Model-Quantum Numbers-Electronic Configuration:

Bohr’s Model, quantum numbers, and electronic configuration are fundamental concepts in atomic theory. Bohr’s Model explains how electrons orbit the nucleus in distinct energy levels. Quantum numbers describe the specific properties of these electron orbits, such as their energy, shape, and orientation. Electronic configuration refers to the arrangement of electrons in these energy levels, determining an element’s chemical behavior and properties. Understanding these concepts is crucial for mastering atomic structure and chemical reactions.

1. According to Bohr’s model, electrons revolve around the nucleus in:
   (a) Random orbits
   (b) Definite circular orbits of fixed energy
   (c) Elliptical orbits
   (d) No orbits at all
   
2. In Bohr’s model, an electron in a permitted orbit:
   (a) Continuously radiates energy
   (b) Does not radiate energy
   (c) Has zero angular momentum
   (d) Collides with the nucleus frequently
   
3. Which quantum number denotes the energy level or shell of an electron?
   (a) Principal quantum number (n)
   (b) Azimuthal quantum number (l)
   (c) Magnetic quantum number (m_l)
   (d) Spin quantum number (m_s)
   
4. The azimuthal quantum number (l) describes:
   (a) The spin of the electron
   (b) The shape of the orbital (subshell)
   (c) The orientation of an orbital
   (d) The maximum number of electrons in a shell
   
5. For the n = 3 shell, the possible values of l (azimuthal quantum number) are:
   (a) 0, 1 only
   (b) 0, 1, 2
   (c) 1, 2, 3
   (d) 0, 2, 3
   
6. The magnetic quantum number (m_l) can take integer values from:
   (a) -l to +l
   (b) 0 to l
   (c) 1 to 2l+1
   (d) -n to +n
   
7. An orbital is defined as:
   (a) A circular path followed by an electron
   (b) A region in space where the probability of finding an electron is high
   (c) The nucleus of an atom
   (d) A point charge
   
8. Which quantum number specifies the orientation of an orbital in space?
   (a) n
   (b) l
   (c) m_l
   (d) m_s
   
9. The spin quantum number (m_s) for an electron can be:
   (a) 0 or +1
   (b) +½ or -½
   (c) 1, 2, or 3
   (d) Any integer value
   
10. According to the Pauli Exclusion Principle:
    (a) Each orbital can accommodate only 2 electrons, each with opposite spins
    (b) Electrons always spin in the same direction
    (c) No two electrons can have the same principal quantum number
    (d) Only one electron can exist in each shell
    
11. Bohr’s model was primarily successful in explaining the atomic spectrum of:
    (a) Helium
    (b) Lithium
    (c) Hydrogen
    (d) All multi-electron atoms
    
12. In the Bohr model, when an electron jumps from a higher orbit to a lower orbit, it:
    (a) Absorbs a photon
    (b) Remains neutral
    (c) Emits a photon
    (d) Changes into a proton
    
13. Which rule states that electrons are filled in order of increasing orbital energy?
    (a) Pauli Exclusion Principle
    (b) Hund’s Rule
    (c) Aufbau Principle
    (d) Dalton’s Law
    
14. Hund’s Rule deals with:
    (a) Maximum multiplicity in degenerate orbitals
    (b) Electrons pairing with opposite spins in the same orbital
    (c) Filling orbitals from lower to higher energy
    (d) Limiting each orbital to 2 electrons
    
15. The total number of orbitals in the third shell (n=3) is:
    (a) 3
    (b) 9
    (c) 4
    (d) 1
    
16. Which electronic configuration violates the Pauli Exclusion Principle?
    (a) ↑↓ in the same orbital
    (b) ↑ in orbital 1, ↑ in orbital 2
    (c) Two electrons in the same orbital with the same spin
    (d) Single electrons in separate orbitals
    
17. The (n + l) rule helps determine:
    (a) The maximum number of electrons per subshell
    (b) The order in which orbitals are filled (Aufbau principle)
    (c) The spin direction of electrons
    (d) The shape of d orbitals
    
18. The orbital angular momentum depends on:
    (a) Principal quantum number (n)
    (b) Azimuthal quantum number (l)
    (c) Spin quantum number (m_s)
    (d) Magnetic quantum number (m_l)
    
19. Bohr’s model introduces the concept of:
    (a) Uncertainty principle
    (b) Quantized energy levels
    (c) Orbital shapes (s, p, d)
    (d) Electron clouds
    
20. In the quantum mechanical model, an electron’s position is described by:
    (a) A definite circular path
    (b) A region of probability (orbital)
    (c) A fixed radius from the nucleus
    (d) Complete certainty of location
    
21. The 4th shell (n=4) can theoretically hold a maximum of:
    (a) 8 electrons
    (b) 32 electrons
    (c) 18 electrons
    (d) 16 electrons
    
22. For a given n, the number of subshells (l values) is:
    (a) n
    (b) n+1
    (c) 2n
    (d) n-1
    
23. The s orbital (l=0) has how many possible orientations (m_l values)?
    (a) 1
    (b) 2
    (c) 3
    (d) 5
    
24. Electron configuration of carbon (Z=6) in ground state is:
    (a) 1s² 2s² 2p²
    (b) 1s² 2s² 2p⁴
    (c) 1s² 1p⁴
    (d) 1s² 2p⁴
    
25. The maximum number of electrons in any p-subshell is:
    (a) 2
    (b) 6
    (c) 10
    (d) 14
    
26. In the n=2 shell, which subshells are present?
    (a) s only
    (b) s and p
    (c) p and d
    (d) s, p, and d
    
27. Hund’s Rule states that in degenerate orbitals, electrons:
    (a) Pair up first before occupying the next orbital
    (b) Must have opposite spins if in the same orbital
    (c) Occupy orbitals singly with parallel spins as far as possible
    (d) Have no preference for spin orientation
    
28. Which set of quantum numbers is valid for an electron in the 3p orbital?
    (a) n=3, l=1, m_l=0, m_s=+½
    (b) n=3, l=2, m_l=2, m_s=0
    (c) n=1, l=0, m_l=0, m_s=+½
    (d) n=3, l=3, m_l=-3, m_s=+½
    
29. Orbital capacity is governed by:
    (a) Aufbau principle
    (b) Pauli Exclusion Principle
    (c) Hund’s Rule
    (d) Heisenberg principle
    
30. The maximum number of electrons that can fit into any single orbital is:
    (a) 1
    (b) 2
    (c) 3
    (d) 4
    

Answer Key

1. (b) Bohr’s model describes electrons in circular orbits of fixed energy.
2. (b) In Bohr’s model, electrons in allowed orbits do not radiate energy.
3. (a) n is the principal quantum number (energy level/shell).
4. (b) l describes the shape of the orbital (subshell).
5. (b) For n=3, l=0 (s), 1 (p), 2 (d).
6. (a) m_l ranges from -l to +l.
7. (b) Orbital = region in space with high probability of finding electron.
8. (c) m_l indicates orbital orientation.
9. (b) Spin can be +½ or -½.
10. (a) Each orbital can hold max 2 e- with opposite spins (Pauli principle).
11. (c) Bohr’s model explained hydrogen’s emission spectrum well.
12. (c) Electron transition from higher to lower orbit emits a photon.
13. (c) Aufbau Principle: fill lower-energy orbitals first.
14. (a) Hund’s Rule: maximize parallel spins in degenerate orbitals first.
15. (b) For n=3, total orbitals = 3s (1) + 3p (3) + 3d (5) = 9.
16. (c) Two electrons in the same orbital with same spin violates Pauli.
17. (b) (n + l) rule = orbital filling order (lower n+l fills first).
18. (b) Orbital angular momentum depends on l.
19. (b) Bohr introduced quantized energy levels for electrons.
20. (b) Quantum mechanical model uses orbitals (probability regions).
21. (b) n=4 shell can hold 2n² = 2(4²)=32 electrons.
22. (a) Number of subshells = n for a given n.
23. (a) s orbital (l=0) → m_l=0 → 1 orientation.
24. (a) Carbon: 1s² 2s² 2p².
25. (b) p-subshell can hold 6 electrons total (3 orbitals × 2 each).
26. (b) For n=2, we have 2s and 2p.
27. (c) Hund’s Rule: singly occupy degenerate orbitals with parallel spins first.
28. (a) 3p: n=3, l=1, m_l=-1,0,+1, m_s=±½. Example: (3,1,0,+½).
29. (b) Pauli Exclusion Principle sets orbital capacity limit (2 e- per orbital).
30. (b) Maximum of 2 electrons per orbital.