Arsenic (As)
Metalloid · p-block · period 4 · group 15
Grey, brittle, metallic-looking metalloid (also a yellow non-metallic form).
Arsenic (symbol As) is chemical element number 33, a metalloid in group 15, period 4 of the periodic table. Its standard atomic weight is 74.922 and its electron configuration is [Ar] 3d10 4s2 4p3. At room temperature it is a solid. A famous poison — nearly tasteless, and once hard to detect in a body.
Properties
| Atomic number | 33 |
|---|---|
| Atomic mass | 74.922 |
| Category | Metalloid |
| Block | p-block |
| Group · Period | 15 · 4 |
| Electron configuration | [Ar] 3d10 4s2 4p3 |
| Electrons per shell | 2, 8, 18, 5 |
| State at 25 °C | solid |
| Melting point | — |
| Boiling point | 887 K |
| Density | 5.727 g/cm³ |
| Electronegativity (Pauling) | 2.18 |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1250 · Albertus Magnus |
Key facts about Arsenic
- A famous poison — nearly tasteless, and once hard to detect in a body.
- Contaminates groundwater in parts of South Asia, a major public-health problem.
- Gallium arsenide is a fast semiconductor used in phone and satellite electronics.
- Was used in green Victorian wallpaper dyes, with deadly results.
What Arsenic is used for
Semiconductor doping, gallium-arsenide chips, wood preservatives (now restricted), lead alloys, historically pesticides.
Where it sits in the periodic table
Arsenic is in group 15, period 4, of the p-block. Its electron configuration [Ar] 3d10 4s2 4p3 means its outermost shell holds 5 electrons, which is what places it here and explains much of its chemistry. See Arsenic on the interactive table →
Arsenic — frequently asked questions
What is Arsenic used for?
Semiconductor doping, gallium-arsenide chips, wood preservatives (now restricted), lead alloys, historically pesticides.
Is Arsenic radioactive?
No. Arsenic has at least one stable isotope and is not radioactive.
What is the electron configuration of Arsenic?
Arsenic has the electron configuration [Ar] 3d10 4s2 4p3, which is 2, 8, 18, 5 electrons per shell.
What group and period is Arsenic in?
Arsenic is in group 15, period 4, in the p-block. Its outer shell holds 5 electrons.
Who discovered Arsenic?
Arsenic was discovered in 1250 by Albertus Magnus.