Arsenic (As)
Element 33 · Metalloid · Solid at 25 °C · Group 15, Period 4
Arsenic is history's most infamous poison, yet gallium arsenide semiconductors are essential to lasers and high-speed electronics.
On the periodic table, arsenic sits in group 15 — the pnictogens (nitrogen group) — in period 4. It is one of 6 elements classified as a metalloid, and at room temperature (25 °C) it is a solid.
Metalloids line the zig-zag “staircase” between the metals and nonmetals and behave a bit like both: they look metallic but are brittle and conduct electricity only moderately well. That in-between conductivity — a semiconductor's — is exactly what modern electronics is built on.
Properties of arsenic
| Atomic number (Z) | 33 |
|---|---|
| Symbol | As |
| Atomic mass | 74.922 |
| Category | Metalloid |
| Group | 15 |
| Period | 4 |
| Block | p-block |
| Metal / nonmetal | Metalloid |
| State at 25 °C | Solid |
| Electron configuration | [Ar] 3d10 4s2 4p3 |
| Electronegativity (Pauling) | 2.18 |
| Melting point | 817 °C (1,090.15 K / 1,502.6 °F) |
| Boiling point | 616 °C (889.15 K / 1,140.8 °F) |
| Density | 5.727 g/cm³ |
Position in the periodic table
Arsenic shares group 15 — the pnictogens (nitrogen group) with Nitrogen (N), Phosphorus (P), Antimony (Sb), Bismuth (Bi), Moscovium (Mc). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.
Physical properties
Arsenic melts at 817 °C (1,090.15 K / 1,502.6 °F) and boils at 616 °C (889.15 K / 1,140.8 °F), giving it a liquid range of about -201 °C at standard pressure.
Its density is 5.727 g/cm³.
See also: the interactive periodic table, how to read the periodic table, metals, nonmetals & metalloids.