Arsenic
metalloid · period 4 · group 15 (pnictogens) · p-block
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal.
What the numbers say
At standard temperature and pressure Arsenic is a solid, sitting in period 4, group 15 of the p-block.
Its melting point of 1090 K (817 °C) is the 62nd highest of the 110 elements with a measured value — mid-range among the elements.
At 5.727 g/cm³ it is the 60th densest of 96 elements with a quoted density.
Pauling electronegativity is 2.18. Paired with oxygen (3.44) that is a difference of 1.26, which puts the bond polar covalent — oxides here tend to be semiconducting or refractory rather than salt-like.
In the solid state it takes a simple trigonal structure.
It is reported in 4 oxidation states (-3, 2, 3, 5), which sets how many distinct compounds and phases it can form.
First identified in 1250.
Crystal structure
Solid Arsenic adopts a Simple Trigonal arrangement, in the Trigonal (rhombohedral) system — axes a = b = c (rhombohedral setting), angles α = β = γ ≠ 90°. Symmetry controls the anisotropy of stiffness and thermal expansion, and the available slip systems set how far the metal deforms before it fractures.
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing As — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 8 · M 18 · N 5
Properties
| Atomic number | 33 |
|---|---|
| Atomic mass | 74.9215956 u |
| Series | metalloid |
| Group | 15 |
| Period | 4 |
| Block | p-block |
| Phase at STP | Solid |
| Density | 5.727 g/cm³ |
| Melting point | 1090 K (817 °C) |
| Boiling point | 887 K (614 °C) |
| Electronegativity (Pauling) | 2.18 |
| Electron configuration | [Ar] 3d¹⁰ 4s² 4p³ |
| Crystal structure | Simple Trigonal |
| Oxidation states | -3,2,3,5 |
| Discovered | 1250 |
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See As in context with all 118 elements.
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