Aufbau orbital filling order from 1s to 7p
The Aufbau configuration of orbitals from 1s to 7p (often written as “list the aufbau configuration of orbiys from 1s to 7p”) is the standard subshell ordering used to build electron configurations by increasing orbital energy in multi-electron atoms.
Orbital labels, quantum numbers, and capacity
A subshell label such as 3p contains a principal quantum number \(n\) and an angular momentum type \( \ell \) (s, p, d, f). For a given \( \ell \), the number of orbitals and the maximum number of electrons follow directly from quantum mechanics:
\[ \text{Number of orbitals in a subshell} = 2\ell+1, \qquad \text{Maximum electrons in a subshell} = 2(2\ell+1). \]
| Subshell type | \( \ell \) | Orbitals \((2\ell+1)\) | Max electrons \(\,2(2\ell+1)\) | Common notation |
|---|---|---|---|---|
| s | \(0\) | \(1\) | \(2\) | 1s, 2s, 3s, … |
| p | \(1\) | \(3\) | \(6\) | 2p, 3p, 4p, … |
| d | \(2\) | \(5\) | \(10\) | 3d, 4d, 5d, … |
| f | \(3\) | \(7\) | \(14\) | 4f, 5f, … |
Energy ordering and the \(n+\ell\) (Madelung) rule
The Aufbau principle orders subshells by increasing approximate energy in many-electron atoms. A practical ordering rule is:
The quantity \(n+\ell\) ranks subshell energies. Smaller \(n+\ell\) indicates lower energy. When two subshells share the same \(n+\ell\), the smaller \(n\) is lower in energy.
Aufbau filling sequence from 1s to 7p
The resulting filling sequence through 7p is shown below. The table includes the subshell capacity and its \(n+\ell\) value (useful for checking the order).
| Fill order | Subshell | \(n\) | \(\ell\) | \(n+\ell\) | Max electrons |
|---|---|---|---|---|---|
| 1 | 1s | 1 | \(0\) | 1 | 2 |
| 2 | 2s | 2 | \(0\) | 2 | 2 |
| 3 | 2p | 2 | \(1\) | 3 | 6 |
| 4 | 3s | 3 | \(0\) | 3 | 2 |
| 5 | 3p | 3 | \(1\) | 4 | 6 |
| 6 | 4s | 4 | \(0\) | 4 | 2 |
| 7 | 3d | 3 | \(2\) | 5 | 10 |
| 8 | 4p | 4 | \(1\) | 5 | 6 |
| 9 | 5s | 5 | \(0\) | 5 | 2 |
| 10 | 4d | 4 | \(2\) | 6 | 10 |
| 11 | 5p | 5 | \(1\) | 6 | 6 |
| 12 | 6s | 6 | \(0\) | 6 | 2 |
| 13 | 4f | 4 | \(3\) | 7 | 14 |
| 14 | 5d | 5 | \(2\) | 7 | 10 |
| 15 | 6p | 6 | \(1\) | 7 | 6 |
| 16 | 7s | 7 | \(0\) | 7 | 2 |
| 17 | 5f | 5 | \(3\) | 8 | 14 |
| 18 | 6d | 6 | \(2\) | 8 | 10 |
| 19 | 7p | 7 | \(1\) | 8 | 6 |
Diagonal-rule visualization of the same order
Configuration constraints used alongside the Aufbau order
A chemically correct electron configuration combines the filling order with three additional constraints (the energy order does not replace these constraints).
| Constraint | Statement | Immediate consequence for notation |
|---|---|---|
| Pauli exclusion principle | Each orbital holds at most two electrons with opposite spins. | Subshell exponents do not exceed the subshell maximum (s: 2, p: 6, d: 10, f: 14). |
| Hund’s rule | Electrons occupy degenerate orbitals singly before pairing. | Partially filled p, d, f subshells spread electrons across orbitals before doubling up. |
| Aufbau principle | Lower-energy subshells fill before higher-energy subshells in the ground state. | The ordering list (1s → 7p) dictates which subshell exponent increases next. |
Common points of confusion in general chemistry
The placement of 4s before 3d in the Aufbau sequence is standard for building ground-state configurations from low to high energy. In ionic configurations of transition metals, electrons are typically removed from the highest \(n\) level first (often 4s before 3d), reflecting the relative energies after occupation and in the ionic environment.
Small, well-known deviations from a strict Aufbau filling can occur among transition metals (for example, enhanced stability of half-filled or filled d subshells). The ordering list remains the correct baseline; specific exceptions are treated as experimentally established ground-state patterns.