Chemical element · Atomic number 33
Arsenic
Arsenic in the periodic table: atomic number 33, electron configuration, atomic mass, physical data, oxidation states, media credit and visible sources.
Metalloid
solid
74.92159 u
Documented element sampleA documented sample of elemental arsenic, a brittle metalloid.
Image credit: James St. John
Auto-oriented, limited to 1600 × 1200 pixels and re-encoded as WebP; the subject was not altered.
Atomic classification
Shell occupancy
Arsenic in the Bohr shell model
This shows the electron distribution of the neutral atom in a simplified shell model.
- K · n=1
- 2 electrons
- L · n=2
- 8 electrons
- M · n=3
- 18 electrons
- N · n=4
- 5 electrons
- Electron configuration
- [Ar]4s2 3d10 4p3
- Electrons per shell
- 2 · 8 · 18 · 5
- Group
- 15
- Period
- 4
- Block
- P
- Element category
- Metalloid
Physical and chemical properties
- Atomic mass
- 74.92159 u
- Standard state
- solid
- Density
- 5.776 g/cm³
- Melting point
- 1,090 K
- Boiling point
- 887 K
- Electronegativity
- 2.18 (Pauling)
- First ionisation energy
- 9.815 eV
- Oxidation states
- +5, +3, -3
- Discovery
- known since antiquity
Safety and periodic classification
Safety
Safe handling cannot be inferred from Arsenic's position in the periodic table alone. Laboratory, classroom and disposal decisions must follow the documentation for the exact material and its safety data sheet.
Position and comparison
Arsenic is in period 4, group 15 and the P block. Its direct neighbours by atomic number are Germanium and Selenium. The recorded Pauling electronegativity is 2.18. Periodic trends are compared only through the separately sourced neighbouring values.
Sources and scope
PubChem attributes element data to sources including IUPAC, NIST and IAEA. Quanta stores the referenced snapshot locally and leaves unknown values unavailable.
Where Arsenic sits among the 118 elements
The table compares the reported values for Arsenic with every other element that carries the same value in the snapshot. A rank is not a judgement, it is orientation: it says how unusual this value is across the periodic table.
| Value | Arsenic | Position in the data set |
|---|---|---|
| Melting point | 1,090 K | Rank 60 of 103 elements with a reported value. Highest: Carbon. |
| Boiling point | 887 K | Rank 77 of 93 elements with a reported value. Highest: Rhenium. |
| Density | 5.776 g/cm³ | Rank 60 of 96 elements with a reported value. Highest: Osmium. |
| Electronegativity (Pauling) | 2.18 | Rank 24 of 95 elements with a reported value. Highest: Fluorine. |
| Ionisation energy | 9.815 eV | Rank 18 of 102 elements with a reported value. Highest: Helium. |
All values and ranks come from the PubChem Periodic Table snapshot, retrieved on 2026-07-15. Elements without a reported value are excluded, so the population differs per row.
The neighbours of Arsenic in the periodic table
- Place in the table
- Group 15, period 4, P block. Classified as metalloid, solid at standard conditions.
- Direct neighbours
- Atomic number 33. Preceded by Germanium, followed by Selenium.
- Same group
- Same number of outer electrons, and therefore similar reactivity to Nitrogen, Phosphorus, Antimony, Bismuth, Moscovium.
- Discovery
- Recorded in the snapshot as: known since antiquity. Who, where and under what circumstances is not part of that record, so this page carries the sourced year and no discovery narrative.
- Oxidation states
- +5, +3, -3. They follow from the electron configuration [Ar]4s2 3d10 4p3 and indicate which compounds to expect.
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