Arsenic (As) – element 33
Arsenic is a chemical element with the symbol As and atomic number 33. It is a metalloid in group 15 (pnictogens), period 4 of the periodic table (p-block), and is a solid at room temperature.
Arsenic (As) has atomic number 33, atomic mass 74.922 u and electron configuration [Ar] 3d10 4s2 4p3.
Arsenic facts
| Symbol | As |
|---|---|
| Atomic number | 33 |
| Atomic mass | 74.922 u (g/mol) |
| Category | metalloid |
| Group | group 15 (pnictogens) |
| Period | 4 |
| Block | p-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3 |
| Noble-gas notation | [Ar] 3d10 4s2 4p3 |
| Electrons per shell | 2, 8, 18, 5 |
| Valence electrons | 5 |
Bohr model and shells
Arsenic has 33 electrons in 4 shells: 2, 8, 18, 5. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 1090 K (816.9 °C) |
|---|---|
| Density | 5.727 g/cm³ |
| Electronegativity (Pauling) | 2.18 |
| Electron affinity | 77.65 kJ/mol |
| Ionization energies | 947, 1798, 2735 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 24.64 J/(mol·K) |
| Discovered by | Bronze Age |
Use the atomic mass in the molar mass calculator for any formula containing As.
Position in the periodic table
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Frequently asked questions
What is the atomic mass of arsenic?
The atomic mass of arsenic is 74.922 u, so one mole of arsenic atoms weighs 74.922 g.
What is the electron configuration of arsenic?
Arsenic has 33 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p³, or [Ar] 3d¹⁰ 4s² 4p³ in noble-gas notation. Electrons per shell: 2, 8, 18, 5.
How many valence electrons does arsenic have?
Arsenic has 5 valence electrons (group 15).
Is arsenic a metal?
Arsenic is a metalloid: it has properties between metals and nonmetals.
Where is arsenic on the periodic table?
Arsenic is in group 15 (pnictogens), period 4, in the p-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.