Iodine Electron Configuration

Reference for iodine's electron configuration ([Kr] 4d¹⁰ 5s² 5p⁵), orbital box diagram, and key atomic data for I (Z=53).

Z = 53 I Iodine

Iodine — Electron Configuration

Atomic number 53 · Halogen · Period 5, Group 17 · p-block

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁵ [Kr] 4d¹⁰ 5s² 5p⁵ 53 electrons 7 valence e⁻ Standard filling

Group 17 Halogen — 7 Valence Electrons

Iodine follows a standard Aufbau filling (no anomaly). The outer shell is 5s² 5p⁵ — one electron short of the xenon noble-gas configuration. This single vacancy makes iodine highly electronegative and gives it a large electron affinity (295.2 kJ/mol), readily accepting one electron to become I⁻. Its symbol "I" comes from the Greek ioeides (violet-colored).

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 2 2 4s²
4p p orbitals, shell n=4 6 6 4p⁶
4d d orbitals, shell n=4 10 10 4d¹⁰
5s s orbital, shell n=5 2 2 5s²
5p p orbitals, shell n=5 (outer) 5 6 5p⁵
Total 53

Full Configuration

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

All subshells written explicitly.

Noble-Gas Shorthand

[Kr] 4d¹⁰ 5s² 5p⁵

[Kr] = 1s²…4p⁶ (krypton's filled core, Z=36).

Valence Shell

5s² 5p⁵

7 valence electrons. One more → [Xe] noble-gas configuration.

Shell Fill Summary

Shell 1 (n=1) — 1s² 2 / 2 electrons (100%)
Shell 2 (n=2) — 2s² 2p⁶ 8 / 8 electrons (100%)
Shell 3 (n=3) — 3s² 3p⁶ 3d¹⁰ 18 / 18 electrons (100%)
Shell 4 (n=4) — 4s² 4p⁶ 4d¹⁰ 18 / 32 electrons (56%)
Shell 5 (n=5) — 5s² 5p⁵ 7 / 50 electrons (14%)

Shell 5 can hold up to 50 electrons (5s + 5p + 5d + 5f + 5g). Iodine occupies 7 slots (5s² + 5p⁵), leaving one vacancy in 5p. The next element, xenon (Z=54), fills that last 5p slot to achieve a complete octet.

Group 17 Halogens — All Share ns² np⁵

Element Z Noble-Gas Shorthand State (25 °C)
Fluorine (F) 9 [He] 2s² 2p⁵ Gas
Chlorine (Cl) 17 [Ne] 3s² 3p⁵ Gas
Bromine (Br) 35 [Ar] 3d¹⁰ 4s² 4p⁵ Liquid
Iodine (I) 53 [Kr] 4d¹⁰ 5s² 5p⁵ Solid (violet-black)
Astatine (At) 85 [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵ Solid (radioactive)

Summary

Reference for iodine's electron configuration ([Kr] 4d¹⁰ 5s² 5p⁵), orbital box diagram, and key atomic data for I (Z=53).

How it works

  1. The Aufbau principle fills subshells from lowest to highest energy: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p.
  2. Iodine (Z=53) follows a standard (non-anomalous) filling: the 36-electron krypton core fills first, then 4d¹⁰, then 5s², then 5 electrons into 5p.
  3. The 5p subshell holds up to 6 electrons (three p orbitals × 2 spins). Iodine has 5, leaving one vacancy.
  4. With 7 valence electrons (5s² 5p⁵), iodine is one electron short of a noble-gas octet — it strongly attracts an extra electron to form I⁻.
  5. Noble-gas notation replaces the 36-electron krypton core with [Kr], giving [Kr] 4d¹⁰ 5s² 5p⁵ as the standard abbreviated form.
  6. Iodine exists naturally as I₂ (diatomic), a violet-black solid that produces a characteristic purple vapor.

Use cases

  • Quick reference for chemistry homework on Period 5 and Group 17 halogens.
  • Understand why iodine forms I⁻ by gaining one electron to complete its 5p subshell.
  • Visualize orbital filling for iodine using the subshell breakdown and orbital diagram.
  • Learn how iodine's electronegativity (2.66) reflects its near-complete valence shell.
  • Compare iodine to other halogens (F, Cl, Br, At) — all have the ns² np⁵ outer configuration.
  • Teaching aid for octet rule, electron affinity, and Group 17 reactivity trends.
  • Verify the [Kr] 4d¹⁰ 5s² 5p⁵ shorthand and quantum numbers for outer electrons.

Frequently Asked Questions

Last updated: 2026-07-08 · Reviewed by Nham Vu