Atomic number 33
Arsenic
Metalloid
Quick facts
- Atomic mass
- 74.922
- Group
- 15
- Period
- 4
- State (STP)
- solid
- Electronegativity
- 2.18
- Common ox. states
- -3, +3, +5
Properties
Electron configuration
[Ar] 3d¹⁰ 4s² 4p³
- Ionization energy
- 947.0 kJ/mol
- Electron affinity
- 78.0 kJ/mol
- Melting point
- 1090.00 K (816.9 °C)
- Boiling point
- 887.00 K (613.9 °C)
How it bonds
Arsenic mirrors phosphorus: group 15, 3 bonds + 1 lone pair (AsH₃, arsine), with an expanded-octet +5 state (As₂O₅). The reason arsenic is famously poisonous is exactly this similarity — it sneaks into phosphate-using enzymes, then poisons them.