Arsenic
[Ar] 3d¹⁰ 4s² 4p³ · 2 · 8 · 18 · 5
A metalloid known first and foremost as the classic poison. Arsenic is tasteless and odourless and its symptoms mimic cholera, which earned it centuries as the king of poisons and the poison of kings.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
Drag to rotate, scroll to zoom
Atomic properties
- Atomic number
- 33
- Atomic mass
- 74.922 а.е.м.
- Electron configuration
- [Ar] 3d¹⁰ 4s² 4p³
- Electrons per shell
- 2 · 8 · 18 · 5
- Block
- p-block
- Group
- Pnictogens
- Period
- 4
- Electronegativity (Pauling)
- 2.18
- Electronegativity (Allen)
- 2.21
- Atomic radius
- 114 pm
- Covalent radius
- 119 pm
- Van der Waals radius
- 185 pm
- Ionisation energy 1
- 947 kJ/mol
- Ionisation energy 2
- 1 798 kJ/mol
- Ionisation energy 3
- 2 735 kJ/mol
- Ionisation energy 4
- 4 837 kJ/mol
- Ionisation energy 5
- 6 043 kJ/mol
- Electron affinity
- 78 kJ/mol
- Common oxidation states
- -3, +3, +5
- Oxidation states
- -3, -2, -1, +1, +2, +3, +4, +5
Physical properties
- State at 25 °C
- solid
- Density
- 5.727 g/cm³
- Melting point
- 1 090 K · 816.9 °C
- Boiling point
- 887 K · 613.9 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 24.44 kJ/mol
- Heat of vaporisation
- 34.76 kJ/mol
- Specific heat capacity
- 0.329 J/(g·K)
- Thermal conductivity
- 50.2 W/(m·K)
Mechanical properties
- Young's modulus
- 8 GPa
- Shear modulus
- no data
- Bulk modulus
- 22 GPa
- Poisson ratio
- no data
- Mohs hardness
- 3.5
- Brinell hardness
- 1 440 MPa
Electrical and magnetic properties
- Electrical resistivity
- 333 nΩ·m
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- rhombohedral
- Lattice constants
- a = 375.98 pm · c = 1 054.75 pm
Abundance
- In the crust
- 1.8 mg/kg
- In the ocean
- 0.0037 mg/L
- In the universe
- 0.008 mg/kg
- In the human body
- 0.1 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 75As | 100 % | stable | — |
Arsenic-75 is the only stable isotope. Arsenic-74 is used as a positron emitter in research PET imaging.
Discovery
- Year of discovery
- 1250
- Discovered by
- Albertus Magnus
- Where
- Germany
- Origin of the name
- from Greek arsenikon (yellow orpiment)
History
Arsenic compounds served antiquity as pigments and medicines. Elemental arsenic was probably first obtained by Albertus Magnus around 1250. The Russian name comes from the word for mouse: arsenic preparations killed rodents.
Where it occurs
1.8 mg/kg of the crust. The main minerals are arsenopyrite and realgar. Its largest environmental problem is natural groundwater contamination in Bangladesh and West Bengal.
How it is produced
A by-product of copper and gold processing: it volatilises during roasting and is captured as the trioxide.
Role in living things
Some bacteria use arsenate in anaerobic respiration. For humans arsenic is poison: it blocks respiratory-chain enzymes and substitutes for phosphate in ATP.
Safety
Chronic poisoning through drinking water attacks skin and nerves and causes cancer — the WHO estimates tens of millions of people at risk. A lethal dose of the trioxide is around 100 mg.
Uses
- Gallium arsenide in high-frequency electronics and laser diodes
- Doping silicon to make it n-type
- Lead-acid batteries, where arsenic stiffens the grid alloy
- Arsenic trioxide in the treatment of acute promyelocytic leukaemia
Curiosities
- The Marsh test, devised in 1836, was the first reliable courtroom proof of arsenic poisoning.
- Nineteenth-century green wallpaper contained copper arsenite — Paris green — and gave off toxic vapour in damp rooms.
- Arsenic sublimes at 887 K, skipping the liquid phase entirely.
- Arsenic trioxide went from poison to an effective anti-leukaemia drug.