Orbitals in an atom are arranged based on energy levels and sublevels, following the rules of quantum mechanics. Here’s a simple explanation:
1. Energy Levels (Shells)
- Denoted by n = 1, 2, 3…
- The bigger the n, the farther the orbital is from the nucleus and the higher its energy.
2. Sublevels (Subshells)
- Each energy level has sublevels: s, p, d, f
- Number of sublevels = the principal quantum number (n)
- n = 1 → s
- n = 2 → s, p
- n = 3 → s, p, d
- n = 4 → s, p, d, f
3. Order of Filling Orbitals
Electrons fill orbitals from lowest to highest energy, following the Aufbau principle:
Filling order (simplified):
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p
4. Rules to Keep in Mind
- Pauli Exclusion Principle: Each orbital holds max 2 electrons with opposite spins.
- Hund’s Rule: Electrons fill orbitals of the same sublevel singly first, then pair up.
In short:
Orbitals are arranged in shells and subshells, filling from low to high energy, with s → p → d → f shapes, following specific rules.