Selenium (Se): Electron Configuration, Properties and Uses
Selenium (Se): Electron Configuration, Properties and Uses
Electron configuration [Ar] 4s2 3d10 4p4 · group 16 · period 4 · Ar 78.971
Selenium data
- Atomic number
- 34
- Relative atomic mass
- 78.971
- Group
- 16
- Period
- 4
- Block
- p
- Category
- Nonmetal
- Electron configuration
- [Ar] 4s2 3d10 4p4
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
- Electrons per shell
- 2, 8, 18, 6 (K L M N)
- Valence electrons
- 6
- Electronegativity (Pauling)
- 2.55
- First ionisation energy
- 9.752 eV
- Atomic radius (van der Waals)
- 190 pm
- State at room temperature
- Solid
- Melting point
- 220 °C
- Boiling point
- 685 °C
- Density
- 4.809 g/cm³
- Common oxidation states
- +6, +4, −2
- Discovered
- 1817
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 18 · N 6
Orbital diagram (outer electrons)
About selenium
With atomic number 34, selenium (Se) has 34 protons in its nucleus and 34 electrons as a neutral atom. It is a nonmetal in group 16, period 4, p-block. Selenium was first discovered in 1817. Selenium is a solid at room temperature, melting at 220 °C and boiling at 685 °C.
Selenium electron configuration
The electron configuration of selenium is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4, or in short [Ar] 4s2 3d10 4p4. Its electrons occupy 4 shells: K = 2, L = 8, M = 18, N = 6. Selenium has 6 valence electrons in the N shell (4s2 4p4), which is why it sits in group 16. In ionic compounds selenium gains electrons to fill its outer shell: Se2− = [Kr] (like krypton).
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d10(30) → 4p4(34)
Uses of selenium
In industry and the laboratory, selenium turns up in many places, for example CIGS solar cells, decolourising glass, anti-dandruff shampoo (selenium sulfide) and as a trace nutrient. For research and analysis you can browse selenium compounds in the AMI Scientific catalogue.
Safety
Selenium is needed in tiny amounts but is toxic at higher doses. Always read the safety data sheet (SDS) before working with a chemical.
Other elements in group 16
Frequently asked questions
What is the electron configuration of selenium?
The electron configuration of selenium (Se, atomic number 34) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4, or [Ar] 4s2 3d10 4p4 in short. By shell: 2, 8, 18, 6.
How many valence electrons does selenium have?
Selenium has 6 valence electrons.
Which group and period is selenium in?
Selenium is in group 16, period 4, p-block.
What is the atomic mass of selenium?
The relative atomic mass of selenium is 78.971. Use it to calculate molar mass with the molar mass calculator.
Need selenium compounds for your lab?
AMI Scientific is one of the official TCI distributors in Indonesia. Reagents with lot CoA & SDS, formal quotations and tax invoices for universities and laboratories.
Other formulas & calculators: molarity, mole, molality, normality, dilution, titration, pH, buffer, molar mass, ppm, mole fraction, mass percent, periodic table, chemical MSDS.
