Arsenic (symbol As, atomic number 33) is a notoriously toxic metalloid used in semiconductors and, historically, poisons. It is classified as a metalloid and sits in group 15, period 4 of the periodic table.
Overview
Arsenic is the chemical element with atomic number 33 and the symbol As. With a standard atomic weight of 74.922, it is a metalloid. In the periodic table it occupies group 15 and period 4, and under standard conditions it is normally a solid. Arsenic is a notoriously toxic metalloid used in semiconductors and, historically, poisons.
Atomic structure
An atom of Arsenic has 33 protons in its nucleus and, when neutral, 33 electrons arranged in the configuration [Ar] 3d10 4s2 4p3. Its standard atomic weight of 74.922 reflects the natural mix of its stable isotopes.
Discovery and place in the table
Arsenic has been known since antiquity. It follows Germanium (Ge) and precedes Selenium (Se) in order of atomic number.
| Atomic number | 33 |
|---|---|
| Symbol | As |
| Atomic mass | 74.922 |
| Category | Metalloid |
| Group | 15 |
| Period | 4 |
| Electron configuration | [Ar] 3d10 4s2 4p3 |
| Phase at STP | Solid |
| Discovered | Antiquity |