Hund's rule of maximum multiplicity
States that every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin.
What is Hund's rule of maximum multiplicity?
Orbitals within the same subshell that have the same energy (e.g., 2px, 2py, 2pz orbitals).
Key points
- State Hund's rule of maximum multiplicity correctly.
- Apply Hund's rule to write the ground state electron configurations of atoms.
- Explain the significance of parallel spins in degenerate orbitals.
- Predict the magnetic properties (paramagnetic/diamagnetic) of elements based on their electron configurations.
Common exam trap
Pairing electrons in an orbital before all degenerate orbitals are singly occupied.
Definitions
- Term
Degenerate Orbitals
- Meaning
Orbitals within the same subshell that have the same energy (e.g., 2px, 2py, 2pz orbitals).
- Term
Multiplicity (Spin Multiplicity)
- Meaning
A measure of the total spin angular momentum of an atom or molecule, given by (2S+1), where S is the total spin quantum number. Maximizing parallel spins maximizes S and thus multiplicity.
- Term
Parallel Spins
- Meaning
Electrons having the same spin quantum number (both +1/2 or both -1/2).
- Term
Exchange Energy
- Meaning
A quantum mechanical effect that arises when electrons with parallel spins can exchange their positions, leading to a stabilization of the system.
Learning objectives
State Hund's rule of maximum multiplicity correctly.
Apply Hund's rule to write the ground state electron configurations of atoms.
Explain the significance of parallel spins in degenerate orbitals.
Predict the magnetic properties (paramagnetic/diamagnetic) of elements based on their electron configurations.
Prerequisites
Basic understanding of atomic structure (nucleus, electrons).
Knowledge of quantum numbers (n, l, ml, ms).
Understanding of atomic orbitals (s, p, d, f) and their shapes.
Familiarity with the Aufbau principle.
Understanding of the Pauli Exclusion Principle.
Common mistakes
Pairing electrons in an orbital before all degenerate orbitals are singly occupied.
Assigning opposite spins to electrons in singly occupied degenerate orbitals.
Confusing it with the Aufbau principle (energy ordering) or Pauli exclusion principle (max 2 electrons per orbital, opposite spins).
Keywords
Hund's rule
maximum multiplicity
electron configuration
degenerate orbitals
parallel spins
ground state
stability
exchange energy
paramagnetism
diamagnetism
Practice preview
Which of the following electronic configurations violates Hund's rule of maximum multiplicity?…
medium
For which element is the electronic configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵ consistent with Hund's rule?…
medium
Consider the electronic configuration of Nitrogen (atomic number 7). Which of the following orbital diagrams correctly represents the filling of the 2p subshell according to Hund's rule?…
easy