Arsenic (As): electron configuration, atomic mass and facts
Arsenic (As) is element 33 of the periodic table, a metalloid in period 4, group 15. Its electron configuration is [Ar] 3d10 4s2 4p3, with electrons arranged in shells 2, 8, 18, 5, and its standard atomic weight is 74.922 u.
▶ Watch Arsenic’s electrons orbit in the interactive periodic tableArsenic at a glance
| Symbol | As |
|---|---|
| Atomic number | 33 |
| Atomic mass | 74.922 u |
| Category | Metalloid |
| Group | 15 |
| Period | 4 |
| Block | p-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p3 |
| Noble-gas shorthand | [Ar] 3d10 4s2 4p3 |
| Electrons per shell | 2, 8, 18, 5 |
| Outer-shell electrons | 5 |
| Electronegativity (Pauling) | 2.18 |
| State at 20 °C | solid |
Where is Arsenic on the periodic table?
Arsenic is in period 4, group 15, in the p-block. The period number matches its 4 electron shells, and the block names the subshell its last electrons fill. In the same group, Phosphorus sits directly above it and Antimony sits directly below it. Elements in one group have the same number of outer-shell electrons (5 here), which is why they react in similar ways.
How to work out the electron configuration of Arsenic
Put 33 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d¹⁰ (30), 4p³ (33). In shorthand, [Ar] stands for the 18 electrons of argon, giving [Ar] 3d¹⁰ 4s² 4p³.
How electronegative is Arsenic?
Arsenic has a Pauling electronegativity of 2.18, ranking 25 of the 100 elements with a known value (fluorine is highest at 3.98). That is in the middle of the range.
Frequently asked questions
What is the electron configuration of Arsenic?
The electron configuration of Arsenic (As) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p3. In noble-gas shorthand it is written [Ar] 3d10 4s2 4p3.
How many electrons does Arsenic have in each shell?
Arsenic has 33 electrons arranged in shells as 2, 8, 18, 5. It has 5 electrons in its outer shell.
What is the atomic mass of Arsenic?
The standard atomic weight of Arsenic is 74.922 u, so one mole of Arsenic atoms has a mass of about 74.922 g.
Is Arsenic a metal?
Arsenic is a metalloid: its properties sit between those of metals and nonmetals.
Explore nearby elements
More metalloids: Boron, Silicon, Germanium, Antimony, Tellurium. See all elements on the periodic table.