Hund's rule describes the specific way electrons fill orbitals within an atom's subshells.
Understanding Hund's Rule
Hund's rule dictates how electrons are arranged within atomic orbitals, particularly when dealing with orbitals of equal energy (degenerate orbitals), like p, d, and f orbitals within a subshell. The rule focuses on two key principles:
- Single Occupancy First: Electrons will individually occupy each orbital within a subshell before any orbital gets a second electron. This ensures each orbital has at least one electron before any pairing occurs.
- Maximize Spin: When occupying these orbitals individually, all the electrons will have the same spin orientation. This is typically represented as either all spins "up" or all spins "down".
Key Components of Hund's Rule
| Principle | Description | Impact |
|---|---|---|
| Single Occupancy | Each orbital in a subshell is occupied by one electron before any orbital is doubly filled. | Minimizes electron-electron repulsion. |
| Maximized Spin | Electrons in singly occupied orbitals all have the same spin. | Maximizes overall spin angular momentum of the atom. |
Example
Consider the nitrogen atom (N) which has an electron configuration of 1s22s22p3. The 2p subshell contains three p-orbitals, each of which can hold two electrons. According to Hund's rule, in the 2p subshell, the three electrons will each go into a different p-orbital, and they will all have the same spin (either +1/2 or -1/2). It would not be correct to put two electrons in one p-orbital, and one electron in another.
Why Hund's Rule Matters
- Stability: Following Hund's rule leads to a more stable and lower-energy electron configuration within an atom, especially in the ground state.
- Magnetic Properties: Hund's rule has a significant effect on the magnetic properties of atoms and molecules. Unpaired electrons contribute to paramagnetism, while paired electrons cancel each other's magnetic moments.
- Spectroscopy: Understanding Hund’s rule is critical for interpreting atomic spectra.
By adhering to Hund's rule, atoms achieve the most stable electron configuration possible, impacting various chemical and physical properties. The reference defines Hund's rule as: "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."
