Copper Electron Configuration
Reference for copper's anomalous electron configuration ([Ar] 3d¹⁰ 4s¹), orbital box diagram, and key atomic data for Cu (Z=29).
Copper — Electron Configuration
Atomic number 29 · Transition metal · Period 4, Group 11 · d-block
Anomalous Configuration — Aufbau Exception
Expected (Aufbau prediction)
[Ar] 3d⁹ 4s²
9 electrons in 3d, 2 in 4s
Actual (observed)
[Ar] 3d¹⁰ 4s¹
10 electrons in 3d (filled), 1 in 4s
One electron migrates from 4s to complete the 3d subshell. A fully filled 3d¹⁰ subshell releases more exchange energy than a partially filled 3d⁹ 4s² arrangement, making the actual configuration lower in energy.
Subshell Breakdown
| Subshell | Type | Electrons | Max Capacity | Notation |
|---|---|---|---|---|
| 1s | s orbital, shell n=1 | 2 | 2 | 1s² |
| 2s | s orbital, shell n=2 | 2 | 2 | 2s² |
| 2p | p orbitals, shell n=2 | 6 | 6 | 2p⁶ |
| 3s | s orbital, shell n=3 | 2 | 2 | 3s² |
| 3p | p orbitals, shell n=3 | 6 | 6 | 3p⁶ |
| 3d | d orbitals, shell n=3 | 10 | 10 | 3d¹⁰ |
| 4s | s orbital, shell n=4 | 1 | 2 | 4s¹ |
| Total | 29 | |||
Full Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹
All subshells written explicitly.
Noble-Gas Shorthand
[Ar] 3d¹⁰ 4s¹
[Ar] = 1s² 2s² 2p⁶ 3s² 3p⁶ (the filled argon core).
Shell Fill Summary
Shells 1, 2, and 3 are completely filled (2 + 8 + 18 = 28 electrons). Shell 4 holds only the single anomalous 4s electron.
Oxidation States and Ionization
Cu⁺ (cuprous)
[Ar] 3d¹⁰
Loses the single 4s¹ electron. Leaves a completely filled 3d¹⁰ — stable, but Cu⁺ disproportionates in water.
Cu²⁺ (cupric)
[Ar] 3d⁹
Loses 4s¹ and one 3d electron. Most stable in aqueous solution; responsible for the blue color of copper(II) solutions.
Summary
Reference for copper's anomalous electron configuration ([Ar] 3d¹⁰ 4s¹), orbital box diagram, and key atomic data for Cu (Z=29).
How it works
- The Aufbau principle normally fills orbitals from lowest to highest energy: 1s → 2s → 2p → 3s → 3p → 4s → 3d.
- For copper (Z=29), the naive prediction would be [Ar] 3d⁹ 4s², placing 9 electrons in 3d and 2 in 4s.
- Instead, one electron moves from 4s to complete the 3d subshell, giving the actual configuration [Ar] 3d¹⁰ 4s¹.
- A completely filled 3d¹⁰ subshell has maximum exchange energy, making it more stable than the partially filled 3d⁹ 4s².
- The same anomaly occurs in chromium (3d⁵ 4s¹ instead of 3d⁴ 4s²), driven by the extra stability of a half-filled 3d⁵.
- Noble-gas notation replaces the argon core with [Ar], leaving [Ar] 3d¹⁰ 4s¹ as the standard abbreviated form.
Use cases
- Quick reference for chemistry homework on d-block anomalies and Aufbau exceptions.
- Understand why copper's 3d¹⁰ 4s¹ is more stable than the expected 3d⁹ 4s².
- Learn how copper forms Cu⁺ (loses 4s¹) and Cu²⁺ (loses 4s¹ and one 3d) ions.
- Visualize orbital filling for transition metal anomalies using the orbital diagram.
- Compare copper to chromium — both exceptions to the Aufbau principle.
- Teaching aid for exchange energy, Hund's rule, and d-block chemistry lessons.