Arsenic: the essentials
- Name: arsenic
- Symbol: As
- Atomic number: 33
- Relative atomic mass (Ar): 74.921595 (6)
- Standard state: solid at 298 K
- Appearance: metallic grey
- Classification: Semi-metallic
- Group in periodic table: 15
- Group name: Pnictogen
- Period in periodic table: 4
- Block in periodic table: p
- Shell structure: 126.96.36.199
- CAS Registry: 7440-38-2
Arsenic atoms have 33 electrons and the shell structure is 188.8.131.52. The ground state electronic configuration of neutral arsenic is [Ar].3d10.4s2.4p3 and the term symbol of arsenic is 4S3/2.
Elemental arsenic occurs in two solid modifications: yellow, and grey or metallic, with specific gravities of 1.97, and 5.73, respectively. The element is a steel grey, very brittle, crystalline, semimetallic (metalloid) solid. It tarnishes in air, and when heated rapidly oxidises to arsenous oxide which has a garlic odour.
Arsenic and its compounds are poisonous as any reader of "who-done-it" books knows. Upon heating arsenic and some minerals containing arsenic, it sublimes (transfers from the solid to the gaseous state, without passing through the liquid state).
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Arsenic: physical properties
- Density of solid: 5727 kg m-3
- Molar volume: 12.95 cm3
- Thermal conductivity: 50 W m‑1 K‑1
Arsenic: heat properties
- Melting point: 1090 [817 °C (1503 °F)] (under pressure) K
- Boiling point: 887 [614 °C (1137 °F)] (sublimes) K
- Enthalpy of fusion: 20.5 kJ mol-1
Arsenic: atom sizes
- Atomic radius (empirical): 115 pm
- Molecular single bond covalent radius: 121 (coordination number 3) ppm
- van der Waals radius: 188 ppm
- Pauling electronegativity: 2.18 (Pauling units)
- Allred Rochow electronegativity: 2.20 (Pauling units)
- Mulliken-Jaffe electronegativity: 2.26 (20% s orbital)
Arsenic: orbital properties
- First ionisation energy: 944.45 kJ mol‑1
- Second ionisation energy: 1793.58 kJ mol‑1
- Third ionisation energy: 2735.3 kJ mol‑1
- Universe: 8 ppb by weight
- Crustal rocks: 2100 ppb by weight
- Human: 50 ppb by weight
Arsenic: crystal structure
Arsenic: biological data
- Human abundance by weight: 50 ppb by weight
Arsenic, despite its poisonous reputation, may be a necessary ultratrace element for humans. It is a necessary ultratrace element for red algae, chickens, rats, goats, and pigs. A deficiency results in inhibited growth.
Reactions of arsenic as the element with air, water, halogens, acids, and bases where known.
Arsenic: binary compounds
Binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and other compounds of arsenic where known.
Arsenic: compound properties
Bond strengths; lattice energies of arsenic halides, hydrides, oxides (where known); and reduction potentials where known.
Arsenic: historyArsenic was discovered by known since ancient times in unknown at not known. Origin of name: from the Greek word "arsenikon" meaning "yellow orpiment".
Isolation: it is not usually necessary to make arsenic in the laboratory as it is commercially available. Arsenic is found in nature in a number of minerals including realgar (As4S4), orpiment (As2S3), arsenolite (As2O3), and iron minerals such as arsenopyrite (FeAsS) and loellingite (FeAs2). Arsenic is made on an industrial scale by heating appropriate minerals in the absence of air. The arsenic is condensed out as a solid.
FeAsS (700°C) → FeS + As(g) → As(s)