Indium Electron Configuration

Reference for indium's electron configuration ([Kr] 4d¹⁰ 5s² 5p¹), orbital box diagram, valence electron count, and key atomic data for In (Z=49).

Z = 49 In Indium

Indium — Electron Configuration

Atomic number 49 · Post-transition metal · Period 5, Group 13 · p-block

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p¹ [Kr] 4d¹⁰ 5s² 5p¹ 49 electrons 3 valence e⁻ In³⁺ common ion

Group 13 / p-block — First Electron into 5p

Indium (Z=49) is the first Period 5 element to place an electron in the 5p subshell. Its configuration [Kr] 4d¹⁰ 5s² 5p¹ follows straightforward Aufbau filling — no anomalies unlike its neighbor silver (Z=47). The single 5p¹ electron is the valence electron that distinguishes indium's chemistry from cadmium's.

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 (valence) 1 6 5p¹
Total 49

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p¹

All 11 subshells written explicitly.

Noble-Gas Shorthand

[Kr] 4d¹⁰ 5s² 5p¹

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

Valence Electrons

5s² 5p¹ (3 total)

All 3 lost → In³⁺. Rarely In⁺ (loses 5p¹ only).

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 5p¹ 3 / 50 electrons (6%)

Shell 5 can hold up to 50 electrons (5s + 5p + 5d + 5f + 5g). Indium uses 3 slots — 5s² and one of the three 5p orbitals — leaving the 5p subshell mostly empty.

Group 13 — Same s² p¹ Valence Pattern

Element Z Configuration Common Ion
Boron (B) 5 [He] 2s² 2p¹ B³⁺ (covalent)
Aluminum (Al) 13 [Ne] 3s² 3p¹ Al³⁺
Gallium (Ga) 31 [Ar] 3d¹⁰ 4s² 4p¹ Ga³⁺
Indium (In) 49 [Kr] 4d¹⁰ 5s² 5p¹ In³⁺
Thallium (Tl) 81 [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹ Tl³⁺ / Tl⁺

All Group 13 elements share the ns² np¹ valence pattern. Thallium also forms Tl⁺ because the relativistic inert-pair effect stabilizes the 6s² pair, an effect absent for indium.

Summary

Reference for indium's electron configuration ([Kr] 4d¹⁰ 5s² 5p¹), orbital box diagram, valence electron count, and key atomic data for In (Z=49).

How it works

  1. The Aufbau principle fills subshells from lowest to highest energy in order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p.
  2. Indium has 49 electrons, one more than cadmium (Z=48). The 49th electron enters the 5p subshell.
  3. The noble-gas core [Kr] accounts for the first 36 electrons (1s² through 4p⁶).
  4. Beyond the krypton core, 10 electrons fill the 4d subshell and 3 fill the 5th shell (5s² 5p¹).
  5. Noble-gas notation: [Kr] 4d¹⁰ 5s² 5p¹ — [Kr] replaces the filled inner shells through krypton.
  6. Indium's 3 valence electrons (5s² 5p¹) are in shell n=5; losing all three gives In³⁺.

Use cases

  • Quick reference for chemistry homework on post-transition metals and Group 13 electron filling.
  • Understand why indium has 3 valence electrons and forms In³⁺ in most compounds.
  • Visualize the orbital filling for Period 5 p-block elements using the orbital box diagram.
  • Compare indium to aluminum and thallium — its Group 13 neighbors above and below.
  • Teaching aid for Aufbau principle, Hund's rule, and periodic table trends in Period 5.
  • Learn how the 5p¹ configuration relates to indium's role in ITO and semiconductor applications.
  • Verify quantum numbers for the outermost subshells of indium.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu