Arsenic (As)
Arsenic is element 33, a metalloid in period 4, group 15 of the periodic table. At room temperature it is a solid.
Electron configuration [Ar] 3d10 4s2 4p3
Electrons per shell 2, 8, 18, 5
Arsenic data
| Atomic number | 33 |
|---|---|
| Symbol | As |
| Atomic mass | 74.922 u |
| Category | Metalloid |
| Group | 15 |
| Period | 4 |
| Block | p |
| State at 25 °C | solid |
| Melting point | 1090 K (816.9 °C) |
| Boiling point | 887 K (613.9 °C) |
| Density | 5.727 g/cm³ |
| Electronegativity (Pauling) | 2.18 |
| Atomic radius | 119 pm |
| 1st ionization energy | 947 kJ/mol |
| Electron affinity | -78 kJ/mol |
| Oxidation states | -3, +2, +3, +5 |
| Common ion charge | 3− |
| Discovered | Known since antiquity |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through arsenic’s configuration and its ions →
Where arsenic sits
Arsenic belongs to the metalloids. Its Pauling electronegativity of 2.18 is mid-range; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Arsenic FAQ
What is the electron configuration of arsenic?
Arsenic (Z = 33) has the configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p3. In noble-gas shorthand that is [Ar] 3d10 4s2 4p3.
How many valence electrons does arsenic have?
5 (outer shell (n = 4)).
What is the atomic mass of arsenic?
The standard atomic weight of arsenic is 74.922 u, so one mole weighs 74.922 g.
Is arsenic a metal?
Arsenic is a metalloid: it has properties between metals and nonmetals.
What is the charge of a arsenic ion?
Arsenic most commonly forms As3−.