As
Arsenic
Element 33 · Metalloid
Arsenic (As)
Arsenic is a grey metalloid infamous as a poison. Its compounds have also been used as medicine, pesticides and pigments.
- Metalloid
- Period 4
- Group 15
- p-block
- solid at room temperature
Key properties
- Atomic mass
- 74.9216
- u
- Electron configuration
- [Ar] 3d10 4s2 4p3
- Melting point
- 816.9 °C
- 1,090 K
- Boiling point
- 613.9 °C
- 887 K
- Density
- 5.776 g/cm³
- Electronegativity
- 2.18
- Pauling
- Atomic radius
- 185 pm
- van der Waals
- 1st ionisation energy
- 9.815 eV
Compare with every element:Electronegativity chartAtomic radius chartIonisation energy chartDensity chart of the elementsMelting point chartElectron configuration chart
Did you know?
Notable facts about arsenic
- 01
Arsenic was called the “inheritance powder” because it was used to poison wealthy relatives.
- 02
The Marsh test (1836) made arsenic poisoning detectable and helped found forensic toxicology.
- 03
Arsenic trioxide is an effective treatment for a form of leukaemia.
Applications
What is arsenic used for?
- Semiconductors (gallium arsenide)
- Wood preservatives (historically)
- Leukaemia treatment
- Lead alloys for batteries
History
Discovery & name origin
Discovered by
Year
Where
Germany
Name origin
Greek arsenikon, the yellow pigment orpiment; from Persian zarnikh, “golden”.
Atomic structure
Atomic properties
Atomic structure
Atomic properties
- Atomic number
- 33
- Atomic mass
- 74.9216 u
- Group
- 15
- Period
- 4
- Block
- p-block
- Electron configuration
- [Ar] 3d10 4s2 4p3
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
- Electrons per shell
- 2, 8, 18, 5
- Electronegativity (Pauling)
- 2.18
- Electron affinity
- 0.81 eV
- Atomic radius (van der Waals)
- 185 pm
- Stable isotopes
- 1
Oxidation states
Highlighted: common oxidation states (+5, +3, -3).
Successive ionisation energies
Energy to remove each electron in turn (kJ/mol). Big jumps show where a new, inner shell begins.
- 1st947
- 2nd1,798
- 3rd2,735
- 4th4,837
- 5th6,043
- 6th12,310
Physical
Physical properties & colour
Physical
Physical properties & colour
- State at 20 °C
- Solid
- Melting point
- 1,090 K · 816.9 °C · 1,502.3 °F
- Boiling point
- 887 K · 613.9 °C · 1,136.9 °F
- Density
- 5.776 g/cm³
- Molar heat capacity
- 24.64 J/(mol·K)
- Appearance
- Metallic grey
- CPK model colour
- Copied
The CPK colour is the convention used for this element’s atoms in molecular models.
FAQ
Arsenic questions
What is As on the periodic table?
As is the symbol for arsenic, element 33 on the periodic table. It sits in group 15, period 4, in the metalloid category, and has an atomic mass of 74.9216.
What is the atomic number of arsenic?
Arsenic has atomic number 33, so every arsenic atom has 33 protons in its nucleus. Its symbol is As and its atomic mass is 74.9216.
Who discovered arsenic?
Arsenic was discovered by Albertus Magnus in c. 1250 (Germany). The name comes from Greek arsenikon, the yellow pigment orpiment; from Persian zarnikh, “golden”.
What is arsenic used for?
Arsenic is used for: semiconductors (gallium arsenide); wood preservatives (historically); leukaemia treatment; lead alloys for batteries.
Is arsenic a metal?
No. Arsenic is classed as a metalloid, with properties between metals and nonmetals.
What is the electron configuration of arsenic?
The electron configuration of arsenic is [Ar] 3d10 4s2 4p3. Its 33 electrons are arranged in shells as 2, 8, 18, 5.