What is the electron configuration of selenium?

Selenium (Se, Z=34) has the ground-state electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴. Its 34 electrons fill eight subshells across four principal shells.

What is the noble-gas shorthand for selenium?

The condensed notation is [Ar] 3d¹⁰ 4s² 4p⁴, where [Ar] represents the filled 1s² 2s² 2p⁶ 3s² 3p⁶ core shared with argon.

How many valence electrons does selenium have?

Selenium has 6 valence electrons: 2 in the 4s subshell and 4 in the 4p subshell. This matches its Group 16 membership, the same as oxygen and sulfur.

Why does selenium have a partially filled 4p subshell?

With 4 electrons in the 4p subshell, one orbital is paired and two orbitals each hold one electron. Hund's rule fills all three 4p orbitals singly before pairing begins, giving selenium two unpaired 4p electrons.

What oxidation states does selenium form?

Selenium most commonly shows −2 (gaining 2 electrons, as in H₂Se), +4 (in SeO₂), and +6 (in H₂SeO₄). The −2 state arises from its tendency to complete the 4p subshell like its Group 16 relatives.

What block and period is selenium in?

Selenium is in Period 4, Group 16 (VIA), and belongs to the p-block of the periodic table. It is a chalcogen.

How does selenium's configuration compare to sulfur?

Both are Group 16 chalcogens with four half-filled or paired p electrons (sulfur: [Ne] 3s² 3p⁴; selenium: [Ar] 3d¹⁰ 4s² 4p⁴). Selenium adds a filled 3d subshell relative to sulfur, placing it in the fourth period.

Selenium Electron Configuration

Reference for selenium's electron configuration (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴), orbital box diagram, quantum numbers, and key atomic properties.

Z = 34 Se Selenium

Selenium — Electron Configuration

Atomic number 34 · Chalcogen · Period 4, Group 16 · p-block

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴ [Ar] 3d¹⁰ 4s² 4p⁴ 34 electrons 6 valence e⁻

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	4	6	4p⁴
Total		34

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴

All subshells written explicitly.

Noble-Gas Shorthand

[Ar] 3d¹⁰ 4s² 4p⁴

[Ar] = 1s² 2s² 2p⁶ 3s² 3p⁶ (the filled argon core).

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 4p⁴ 6 / 32 electrons (19%)

Shell 4 can hold up to 32 electrons (4s + 4p + 4d + 4f). Selenium uses 6 of those 32 slots.

Orbital Box Diagram

2 electrons (paired) — filled

6 electrons across 3 orbitals — filled

2 electrons (paired) — filled

6 electrons across 3 orbitals — filled

10 electrons across 5 orbitals — filled

2 electrons (paired) — filled

4 electrons — one pair and two unpaired electrons (Hund's rule)

Each box represents one orbital. Opposing arrows show paired electrons with opposite spins (+½ and −½). Selenium's 4p⁴ configuration has one paired orbital and two singly occupied orbitals — consistent with Hund's rule.

Quantum Numbers — Selected Electrons

Electron #	n	l	mₗ	mₛ	Subshell
1	1	0	0	+½	1s
2	1	0	0	−½	1s
3	2	0	0	+½	2s
4	2	0	0	−½	2s
5	2	1	-1	+½	2p
6	2	1	-1	−½	2p
7	2	1	0	+½	2p
8	2	1	0	−½	2p
9	2	1	1	+½	2p
10	2	1	1	−½	2p
11	3	0	0	+½	3s
12	3	0	0	−½	3s
13	3	1	-1	+½	3p
14	3	1	-1	−½	3p
15	3	1	0	+½	3p
16	3	1	0	−½	3p
17	3	1	1	+½	3p
18	3	1	1	−½	3p
19–28	3	2	−2…+2	±½	3d (10 e⁻)
29	4	0	0	+½	4s
30	4	0	0	−½	4s
31	4	1	-1	+½	4p
32	4	1	0	+½	4p
33	4	1	1	+½	4p
34	4	1	-1	−½	4p

n = principal quantum number; l = azimuthal (l=0 → s, l=1 → p, l=2 → d); mₗ = magnetic; mₛ = spin. The 3d block (electrons 19–28) is condensed for readability. Electrons 31–34 occupy the 4p subshell.

Summary

Selenium (Se) has atomic number 34 and the ground-state electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴. This tool displays its full orbital diagram, subshell-by-subshell breakdown, and noble-gas shorthand ([Ar] 3d¹⁰ 4s² 4p⁴), along with a quantum-number table and key physical and chemical properties. It is a reliable reference for students and educators studying atomic structure and periodic-table chemistry.

How it works

The Aufbau principle fills orbitals from lowest to highest energy.
Selenium's 34 electrons fill subshells in Aufbau order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, then 4p.
The 3d subshell holds 10 electrons across five orbitals, all fully paired.
The 4p subshell holds 4 electrons: one orbital is paired and two orbitals are singly occupied — consistent with Hund's rule.
Noble-gas notation replaces the inner filled shells with argon in brackets: [Ar] 3d¹⁰ 4s² 4p⁴.
Selenium is a chalcogen (Group 16) and behaves similarly to oxygen and sulfur.

Use cases

Quick reference for chemistry homework or exam review on d-block and p-block elements.
Visualize how the 3d subshell fills before the 4p subshell in Period 4 elements.
Understand why selenium commonly forms −2, +2, +4, and +6 oxidation states.
Compare selenium to neighboring elements arsenic and bromine in Period 4.
Teaching aid for introductory atomic structure and electron configuration lessons.
Verify quantum numbers for each of selenium's 34 electrons.
Explore how selenium's 4p⁴ configuration makes it similar in chemistry to sulfur.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu

Selenium Electron Configuration

Selenium — Electron Configuration

Subshell Breakdown

Shell Fill Summary

Orbital Box Diagram

Quantum Numbers — Selected Electrons

Identity

Physical Properties

Electronic Properties

Context & Uses

Summary

How it works

Use cases

Frequently Asked Questions

Selenium Electron Configuration

Use the Selenium Electron Configuration

Selenium — Electron Configuration

Subshell Breakdown

Shell Fill Summary

Orbital Box Diagram

Quantum Numbers — Selected Electrons

Identity

Physical Properties

Electronic Properties

Context & Uses

Summary

How it works

Use cases

Frequently Asked Questions