Arsenic (As): Electron Configuration, Properties and Uses
Arsenic (As): Electron Configuration, Properties and Uses
Electron configuration [Ar] 4s2 3d10 4p3 · group 15 · period 4 · Ar 74.922
Arsenic data
- Atomic number
- 33
- Relative atomic mass
- 74.922
- Group
- 15
- Period
- 4
- Block
- p
- Category
- Metalloid
- Electron configuration
- [Ar] 4s2 3d10 4p3
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
- Electrons per shell
- 2, 8, 18, 5 (K L M N)
- Valence electrons
- 5
- Electronegativity (Pauling)
- 2.18
- First ionisation energy
- 9.815 eV
- Atomic radius (van der Waals)
- 185 pm
- State at room temperature
- Solid
- Melting point
- 817 °C (under pressure)
- Boiling point
- 614 °C (sublimes)
- Density
- 5.776 g/cm³
- Common oxidation states
- +5, +3, −3
- Discovered
- ancient times
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 18 · N 5
Orbital diagram (outer electrons)
About arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. It is a metalloid in group 15, period 4, p-block. Arsenic has been known and used since ancient times. At normal pressure arsenic does not melt but sublimes at 614 °C.
Arsenic electron configuration
The electron configuration of arsenic is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3, or in short [Ar] 4s2 3d10 4p3. Its electrons occupy 4 shells: K = 2, L = 8, M = 18, N = 5. Arsenic has 5 valence electrons in the N shell (4s2 4p3), which is why it sits in group 15.
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d10(30) → 4p3(33)
Uses of arsenic
The main uses of arsenic include GaAs semiconductors, lead alloys and the leukaemia drug arsenic trioxide; formerly wood preservatives and pesticides.
Safety
Arsenic and its compounds are highly toxic and carcinogenic. Always read the safety data sheet (SDS) before working with a chemical.
Other elements in group 15
Frequently asked questions
What is the electron configuration of arsenic?
The electron configuration of arsenic (As, atomic number 33) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3, or [Ar] 4s2 3d10 4p3 in short. By shell: 2, 8, 18, 5.
How many valence electrons does arsenic have?
Arsenic has 5 valence electrons.
Which group and period is arsenic in?
Arsenic is in group 15, period 4, p-block.
What is the atomic mass of arsenic?
The relative atomic mass of arsenic is 74.922. Use it to calculate molar mass with the molar mass calculator.
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