Aufbau Pauli Exclusion Hunds Rule - UNSOLVED PRACTICE SET
Chapter: Structure of Atom | Topic: Aufbau Pauli Exclusion Hunds Rule
AUFBAU PAULI EXCLUSION HUNDS RULE - UNSOLVED PRACTICE SET
Topic: Aufbau Pauli Exclusion Hunds Rule
Multiple Choice Questions
Q1. The Aufbau principle states that electrons fill orbitals in order of:
- Decreasing energy
- Increasing energy
- Random order
- Decreasing size
Q2. According to the Pauli exclusion principle:
- No two electrons in an atom can have the same set of four quantum numbers
- Electrons fill degenerate orbitals singly first
- Orbitals are filled in order of increasing energy
- An orbital can hold any number of electrons
Q3. Hund's rule of maximum multiplicity states that:
- Electrons pair up in degenerate orbitals before all orbitals have one electron each
- Electrons occupy degenerate orbitals singly with parallel spins before pairing
- Electrons always have opposite spins in the same orbital
- The most stable configuration has all electrons paired
Q4. The correct order of filling orbitals according to the Aufbau principle is:
- 1s, 2s, 2p, 3s, 3p, 3d, 4s
- 1s, 2s, 2p, 3s, 3p, 4s, 3d
- 1s, 2s, 2p, 3s, 3p, 3d, 4p
- 1s, 2p, 2s, 3s, 3p, 4s, 3d
Q5. The maximum number of electrons that can occupy an orbital is:
- 1
- 2
- 6
- 10
Q6. The (n + l) rule is used to determine:
- The number of electrons in a shell
- The order of filling of orbitals
- The shape of an orbital
- The spin of an electron
Short Answer Questions
Q7. State the Aufbau principle. Why does the 4s orbital fill before the 3d orbital?
Q8. State the Pauli exclusion principle. What is the maximum number of electrons that can be present in the n = 2 shell?
Q9. State Hund's rule of maximum multiplicity. Why do electrons in degenerate orbitals prefer parallel spins?
Q10. What are degenerate orbitals? Give an example.
Q11. Your class teacher is arranging students in a bus with three seats in each row. She first places one student in each seat before making anyone share. Also, students sitting together face opposite directions (one looks forward, one looks back). How is this exactly analogous to Hund's rule and Pauli's principle for electrons filling orbitals?
Q12. Why is the electronic configuration of chromium (Cr, Z = 24) written as [Ar] 3d⁵ 4s¹ instead of [Ar] 3d⁴ 4s²?
Long Answer Questions
Q13. Explain the three fundamental principles governing the filling of electrons in orbitals:
(a) Aufbau principle
(b) Pauli exclusion principle
(c) Hund's rule of maximum multiplicity
Illustrate each principle with a suitable example. Why is the half-filled and fully-filled configuration more stable? Explain with the examples of chromium and copper.
Q14. Describe the (n + l) rule for determining the order of filling of orbitals. Use this rule to explain why:
(a) 4s fills before 3d
(b) 5s fills before 4d
(c) 6s fills before 4f
Write the expected electronic configuration of iron (Z = 26) and explain any exceptions to the expected filling order.
Q15. During a classroom quiz, your teacher presents the following configurations and asks you to identify which violate the three principles:
Configuration A: 1s² 2s² 2pₓ² 2pᵧ⁰ 2p₂⁰
Configuration B: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵ (for Mn, Z = 25)
Configuration C: 1s² 2s² 2p⁶ 3s¹ 3p⁰ (for Mg, Z = 12)
Configuration D: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹ 4s² (for Cu, Z = 29)
(a) Which configuration violates Hund's rule? Explain.
(b) Which configuration violates the Aufbau principle? Explain.
(c) Which configuration is the actual ground state configuration despite appearing to violate the simple Aufbau order? Why is it stable?
(d) Write the correct ground state configuration for the element in Configuration C.
Numerical / Application-Based Problems
Q16. Use the (n + l) rule to determine the correct order of filling for the following orbitals: 3d, 4s, 4p, 3p, 5s, 4d.
(a) Calculate (n + l) for each orbital.
(b) Arrange them in order of increasing energy.
(c) For orbitals with the same (n + l) value, which one fills first? Apply this to resolve between 3d and 4p.
Q17. An element has atomic number 25.
(a) Write its expected electronic configuration following the Aufbau principle.
(b) Write its actual ground state electronic configuration. Explain any deviation.
(c) How many unpaired electrons does it have? Show your reasoning using orbital diagrams.
(d) Is this element paramagnetic or diamagnetic? Explain.
Q18. For the element with atomic number 29 (copper):
(a) Write the electronic configuration you would expect based on simple Aufbau filling.
(b) Write the actual electronic configuration. Explain why the 3d subshell has 10 electrons and the 4s subshell has 1 electron.
(c) How does this relate to the stability of half-filled and fully-filled subshells?
(d) Predict whether the Cu⁺ ion would have the configuration [Ar] 3d⁹ 4s¹ or [Ar] 3d¹⁰. Explain your prediction.