Actinium Electron Configuration
★ Exception to the Aufbau order. Predicted 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f1 6s2 6p6 7s2; measured 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d10 6s2 6p6 6d1 7s2.
Orbital diagram
- Valence electrons
- 3
- Unpaired electrons
- 1
- Block
- f-block
- Magnetism (atom)
- paramagnetic
Electrons per shell
| K (n = 1) | 2 |
|---|---|
| L (n = 2) | 8 |
| M (n = 3) | 18 |
| N (n = 4) | 32 |
| O (n = 5) | 18 |
| P (n = 6) | 9 |
| Q (n = 7) | 2 |
Actinium ion configurations
| Ion | Electrons | Configuration |
|---|---|---|
| Ac3+ | 86 | [Xe] 4f14 5d10 6s2 6p6 |
How to write it
Place 89 electrons into subshells in the Aufbau order (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p), filling s with 2, p with 6, d with 10 and f with 14. Actinium sits in period 7, in the f-block, so its last electron enters a f subshell. Replacing the inner electrons with the previous noble gas gives the shorthand [Rn] 6d1 7s2.
Try actinium and its ions in the calculator, or see the full actinium data sheet.
Actinium electron configuration FAQ
What is the electron configuration of actinium?
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 6d¹ 7s². Shorthand (noble gas) notation: [Rn] 6d¹ 7s².
What is the noble gas configuration of actinium?
[Rn] 6d¹ 7s². The bracket stands for the Rn core electrons.
Why is actinium’s electron configuration an exception?
The simple filling (Aufbau) order predicts 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹ 6s² 6p⁶ 7s², but the measured ground state is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 6d¹ 7s². Shifting an electron gives a lower overall energy because the subshells involved are very close in energy.
How many valence electrons does actinium have?
3 (2 outer s + 1 d electrons; 2 in the outermost shell).
How many unpaired electrons does actinium have?
1 in the ground state, following Hund’s rule. An atom with unpaired electrons is paramagnetic.
What is the electron configuration of Ac3+?
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶ (86 electrons).