Arsenic (As)
[Ar] 3d¹⁰ 4s² 4p³. 3 unpaired electrons, period 4, group 15, p block.
Element or ion
Type a symbol, a name or an atomic number, add a charge such as Fe3+ or Cl-, or tap an element in the table. Orbitals fill from m = −l up, spin +½ first.
AsArsenic, Z = 33, 74.922 u
[Ar] 3d10 4s2 4p3
In full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p³
- Blockp block
- Period4
- Group15
- Valence5
- Unpaired3
- MagneticPara
Last electron 4p
- n4shell
- l1p subshell
- m+1orbital
- s+½spin up
Step by step
- Arsenic has 33 electrons.
- Fill in (n + l) order: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p³.
- Write the subshells in order of n: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p³.
- Replace the argon core with [Ar]: [Ar] 3d¹⁰ 4s² 4p³.
Arsenic (As): the numbers
| Atomic number | 33 |
|---|---|
| Atomic mass | 74.922 u |
| Period | 4 |
| Group | 15 |
| Block | p block |
| Valence electrons | 5 |
| Unpaired electrons | 3 |
| Magnetic | paramagnetic |
| Last electron | 4p: n = 4, l = 1, m = +1, s = +1/2 |
Arsenic (As): quick answers
What is the electronic configuration of arsenic?
Arsenic has 33 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p³, or [Ar] 3d¹⁰ 4s² 4p³ in short.
How many unpaired electrons does arsenic have?
Arsenic has 3 unpaired electrons, so it is paramagnetic. Put one electron in each box of a subshell before pairing (Hund’s rule) to see them.
What are the quantum numbers of the last electron of arsenic?
The last electron goes into 4p: n = 4, l = 1, m = +1, s = +1/2. Orbitals fill from m = −l up, spin +½ first.