Hund's Rule: Definition and Examples in Chemistry

📚 Quick Study Guide

• ⚛️ Hund's Rule states that electrons will individually occupy each orbital within a subshell before any orbital is doubly occupied.
• ⬆️ All electrons in singly occupied orbitals have the same spin (maximize total spin).
• 🧪 This minimizes electron-electron repulsion and leads to a more stable configuration.
• 📝 Hund's Rule is applicable only when dealing with degenerate orbitals (orbitals with the same energy level).
• 💡 Exceptions exist, especially in heavier elements, but Hund's Rule is generally a good guideline for lighter elements.

Practice Quiz

1. Which statement best describes Hund's Rule?
1. Electrons always pair up in the lowest energy orbital.
2. Electrons individually occupy each orbital before pairing up in the same orbital.
3. Electrons always have opposite spins.
4. Electrons fill orbitals from highest to lowest energy.
2. What is the primary reason behind Hund's Rule?
1. To maximize the number of paired electrons.
2. To minimize electron-electron repulsion.
3. To maximize the energy of the atom.
4. To minimize the number of unpaired electrons.
3. Consider a $p$ subshell, which has three orbitals. According to Hund's Rule, how will 4 electrons fill these orbitals?
1. All four electrons will pair up in one orbital, leaving the other two empty.
2. Two orbitals will have paired electrons, and one orbital will be empty.
3. Two orbitals will have one electron each, with the same spin, and one orbital will have a pair.
4. Three orbitals will have one electron each, with the same spin, and one orbital will have another electron paired in one of the three orbitals.
4. Which of the following electronic configurations violates Hund's Rule? (Consider only the last subshell configuration)
   1. $2p^3$: ↑↓ ↑
   2. $2p^3$: ↑ ↑ ↑
   3. $2p^4$: ↑↓ ↑ ↑
   4. $2p^2$: ↑ ↑
5. For a given electronic configuration, Hund's Rule helps determine the term symbol corresponding to the __________ energy level.
   1. Highest
   2. Lowest
   3. Average
   4. Most probable
6. Which element's ground state electronic configuration is best described by applying Hund's Rule to its *p* orbitals?
1. Beryllium (Be)
2. Carbon (C)
3. Neon (Ne)
4. Magnesium (Mg)
7. What quantum number is maximized when applying Hund's Rule?
   1. Principal quantum number ($n$)
   2. Azimuthal quantum number ($l$)
   3. Magnetic quantum number ($m_l$)
   4. Spin quantum number ($m_s$)