SPDF Orbital Models
All 118 Elements

SPDF stands for the four types of atomic orbital subshells: s (sharp), p (principal), d (diffuse), and f (fundamental). These letters originated from early spectroscopy observations of atomic emission lines. Each subshell has a different shape: s orbitals are spherical, p orbitals are dumbbell-shaped, d orbitals have four-lobed shapes, and f orbitals have complex multi-lobed shapes.

The Aufbau principle (German: "building up") states that electrons fill atomic orbitals starting from the lowest energy level upward. The filling order follows the Madelung rule: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p.

The Bohr model shows electrons in simple circular shells (K, L, M...) numbered by energy level. The SPDF model (quantum mechanical model) shows electrons in subshells (1s, 2s, 2p, 3s...) with specific shapes and orientations. The SPDF model is more accurate — it predicts the actual three-dimensional probability distribution of electrons, which the Bohr model cannot.

Each individual orbital (s, p, d, or f) holds a maximum of 2 electrons with opposite spins (Pauli exclusion principle). Subshell capacities: s subshell = 1 orbital = 2 electrons max. p subshell = 3 orbitals = 6 electrons max. d subshell = 5 orbitals = 10 electrons max. f subshell = 7 orbitals = 14 electrons max.

Hund's rule states that electrons occupy empty orbitals within the same subshell before pairing in the same orbital. This maximizes the total spin and minimizes electron-electron repulsion. For example, in carbon (1s² 2s² 2p²), the two 2p electrons occupy separate 2p orbitals with parallel spins rather than pairing in one 2p orbital.

The Pauli exclusion principle states that no two electrons in an atom can have the precise same four quantum numbers. In practice, this means a single orbital can hold a maximum of two electrons, and they must have opposite spins (up and down).

Because orbitals fill in order of increasing energy. Due to quantum penetration effects, the 4s orbital is slightly lower in energy than the 3d orbital, so electrons fill 4s first according to the Madelung rule.

Copper is an exception to the Aufbau principle. Instead of [Ar] 4s² 3d⁹, one electron from 4s moves to 3d to fully complete the d-subshell. The correct configuration is [Ar] 4s¹ 3d¹⁰.

The periodic table is divided into s, p, d, and f blocks based on the outermost subshell being filled. Groups 1-2 are the s-block, 13-18 are p-block, transition metals are d-block, and Lanthanides/Actinides are f-block.

Also known as condensed configuration, it represents the inner electron shells by substituting them with the symbol of the nearest preceding noble gas. For example, Sodium (1s² 2s² 2p⁶ 3s¹) becomes [Ne] 3s¹.