What is the electron configuration of astatine?

The full configuration is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p5. The shorthand noble-gas notation is [Xe] 4f14 5d10 6s2 6p5.

How many valence electrons does astatine have?

Astatine has 7 valence electrons in the n=6 valence shell (6s2 6p5), which is why it belongs to Group 17 (the halogens) and typically forms a -1 oxidation state.

Why does astatine's configuration include a 4f14 block?

Astatine (Z=85) comes after the lanthanide series (elements 57–71), so the 4f subshell is fully filled before the 5d and 6p subshells are populated. This is a consequence of the Aufbau principle and the relative energies of subshells.

Is astatine the rarest naturally occurring element?

Yes. Astatine is the rarest naturally occurring element in Earth's crust — estimates suggest less than 30 grams exist at any one time, entirely as short-lived decay products. Its most stable isotope, At-210, has a half-life of only 8.1 hours.

How does astatine's configuration compare to iodine?

Iodine (Z=53) has the configuration [Kr] 4d10 5s2 5p5. Astatine sits directly below iodine in the periodic table and has one additional filled 4f and 5d shell, giving [Xe] 4f14 5d10 6s2 6p5. Both share the same outer s2p5 valence pattern.

Astatine Electron Configuration

Look up the full and shorthand electron configuration for Astatine (At, Z=85) with an interactive subshell breakdown.

Element 85 — Period 6, Group 17

Astatine

Radioactive Halogen

Atomic number 85

Valence e− 7

Block p-block

Electrons 85

Notation

Full Electron Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁵

Total electrons: 85 • All subshells listed in shell order by principal quantum level.

Subshell Breakdown

Subshell	Electrons	Max capacity	Running total	Fill bar

* Highlighted rows are the outer (valence-region) subshells beyond [Xe].

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Summary

Look up the full and shorthand electron configuration for Astatine (At, Z=85) with an interactive subshell breakdown.

How it works

Select the notation you want: full, shorthand (noble gas), or subshell breakdown.
The full configuration lists every subshell from 1s through 6p.
The shorthand uses [Xe] to replace the 54 inner electrons, showing only the valence and outer subshells.
The subshell breakdown displays electron counts, maximum capacity, and fill levels for each subshell.
Use the copy button to grab the notation for use in assignments or notes.

Use cases

Verify astatine's electron configuration for chemistry coursework.
Understand why astatine is a halogen with 7 valence electrons (like fluorine, chlorine, and iodine).
Compare Period 6 element configurations side by side.
Study the role of 4f and 5d subshells in post-xenon elements.
Prepare for AP Chemistry or university-level inorganic chemistry exams.

Frequently Asked Questions

Last updated: 2026-09-13 · Reviewed by Nham Vu