Element 33 · Metalloid
Arsenic (As) — Element 33
Greek arsenikos
Arsenic (As) is a metalloid in Period 4, Group 15 of the periodic table with atomic number 33, standard atomic weight 74.922 u, and ground-state electron configuration [Ar] 3d¹⁰ 4s² 4p³. At standard temperature and pressure it is classified as a solid with 5 valence electrons and common oxidation states -3, +3, +5.
Semiconductors, wood preservatives
What are the atomic properties and physical constants of Arsenic?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 33
- Standard atomic mass
- 74.922 u
- Chemical family
- Metalloid
- Ground-state configuration
- [Ar] 3d¹⁰ 4s² 4p³
- Electrons per shell
- 2, 8, 18, 5
- Valence electrons
- 5
- Common ion charges / oxidation states
- -3, +3, +5
- Phase at STP
- Solid
- Pauling electronegativity
- 2.18 Pauling
- First ionization energy
- 947 kJ/mol
- Atomic radius
- 114 pm
- Melting point
- 817 °C
- Boiling point
- 614 °C
- Discovery year
- Ancient
- Table coordinate
- Period 4, Group 15
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Arsenic’s shells?
A neutral Arsenic atom contains 33 electrons distributed across 4 occupied principal energy shells ([Ar] 3d¹⁰ 4s² 4p³). The table below compares Arsenic’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in As | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 5 e⁻ | 32 e⁻ |
Frequently Asked Questions about Arsenic (As)
What is the atomic mass and atomic number of Arsenic (As)?
Arsenic (As) has atomic number Z = 33 (33 protons in its nucleus) and an IUPAC standard atomic weight of 74.922 u. It sits in Period 4, Group 15 and is classified as a metalloid.
What is the ground-state electron configuration of Arsenic?
The neutral ground-state electron configuration of Arsenic (Z = 33) is [Ar] 3d¹⁰ 4s² 4p³. Across its 4 occupied principal shells (n = 1 to n = 4), the electrons per shell are 2, 8, 18, 5, with 5 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Arsenic?
Arsenic commonly forms -3, +3, +5 oxidation states or ion charges in compounds. Its Pauling electronegativity is 2.18 and its first ionization energy is 947 kJ/mol.
When was Arsenic discovered and what is it used for?
Arsenic was discovered in Ancient (Greek arsenikos). Semiconductors, wood preservatives
How does Arsenic compare to neighboring elements?
Other metalloid elements: