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Oxidation & Electrons | Appearance & Characteristics Reactions | Compounds | Radius | Conductivity Abundance & Isotopes 
Arsenious acid - a poison. |
General:
| Name: Arsenic | Symbol: As |
| Type: Metalloid, Nitrogen group | Atomic weight: 74.9216 |
| Density @ 293 K: 5.776 g/cm3 | Atomic volume: 12.97 cm3/mol |
| Discovered: Arsenic has been known since antiquity as the sulfide. Aristotle, in the fourth century BC, refers to "sandarach", renamed arhenicum by his student Theophrastus of Eresos. Olympiodorus of Thebes (5th century AD) roasted arsenic sulfide and obtained white arsenic (As2O3). Albertus Magnus (1193-1280) was the first to state that arsenic has a metal-like nature. In De Mineralibus he described how the metal could be obtained by heating orpiment (As2S3) with soap. | |
States
| State (s, l, g): solid | |
| Melting point: 1090 K (817 oC) | Boiling point: 887 K (614 oC) |
| Note: At normal pressures arsenic does not melt when heated, it sublimes - i.e. when heated, arsenic undergoes a phase change directly from solid to gas, much like dry ice (solid carbon dioxide) does. The melting point quoted above is under a pressure of 28 atmospheres. | |
Energies
| Specific heat capacity: 0.33 J/gK | Heat of atomization: 303 kJ mol-1 |
| Heat of fusion: 24.44 kJ mol-1 | Heat of vaporization (sublimation): 32.4 kJ mol-1 |
| 1st ionization energy: 946.5 kJ mol-1 | 2nd ionization energy: 1797.8 kJ mol-1 |
| 3rd ionization energy: 2735.4 kJ mol-1 | Electron affinity: 78 kJ mol-1 |
Oxidation & Electrons
| Shells: 2,8,18,5 | Electron configuration: [Ar] 3d10 4s2 4p3 |
| Minimum oxidation number: -3 | Maximum oxidation number: 5 |
| Min. common oxidation no.: -3 | Max. common oxidation no.: 5 |
| Electronegativity (Pauling Scale): 2.18 | Polarizability volume: 4.3 Å3 |
Appearance & Characteristics
| Structure: rhombohedral; layers of 6-member rings | Color: gray |
| Hardness: 3.5 mohs | |
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Harmful effects:
Arsenic is immediately dangerous to life or health at 5 mg m-3. Our bodies do not readily absorb the element itself, hence pure arsenic is much less dangerous than As(III) compounds such as AsH3 and As2O3 which are absorbed easily and are carcinogenic with high toxicity. Characteristics: Arsenic occurs in three distinct solid forms. Gray arsenic is the most common. It has a metallic sheen and conducts electricity. Yellow arsenic is metastable, is a poor electrical conductor and does not have a metallic sheen. It is prepared by cooling gray arsenic vapor in liquid air. It reverts to gray arsenic at room temperature. Black arsenic can be prepared by cooling arsenic vapor at 100 oC - 200 oC. It is glassy, brittle and a poor electrical conductor. Uses: As a result of its toxicity, arsenic compounds are used in wood preservation and insecticides. Gallium arsenide (GaAs) is a semiconductor used in laser diodes and LEDs. Small amounts of arsenic (less than two percent) can be used in lead alloys for ammunition. Despite its potential toxicity, arsenic is also an essential element, necessary to our physiology. A level of 0.00001% is needed for growth and for a healthy nervous system. |
Reactions
| Reaction with air: mild, w/ht ⇒ As4O6 | Reaction with 6 M HCl: none |
| Reaction with 15 M HNO3: mild, w/ht ⇒ H3AsO4, NOx | Reaction with 6 M NaOH: none |
Compounds
| Oxide(s): As2O3 | Chloride(s): AsCl3 AsCl5 |
| Hydride(s): AsH3 |
Radius
| Atomic radius: 115 pm | Ionic radius (1+ ion): pm |
| Ionic radius (2+ ion): pm | Ionic radius (3+ ion): 72 pm |
| Ionic radius (2- ion): pm | Ionic radius (1- ion): pm |
Conductivity
| Thermal conductivity: 50.2 W m-1 K-1 | Electrical conductivity: 3.85 x 10-6 S cm-1 |
Abundance & Isotopes
| Abundance earth's crust: 1.8 parts per million by weight, 0.5 parts per million by moles | |
| Abundance solar system: 12 parts per billion by weight, 0.21 parts per billion by moles | |
| Cost, pure: $320 per 100g | |
| Cost, bulk: $ per 100g | |
| Source: Most arsenic is obtained as a by-product of processing gold, silver, copper, and other metal ores. | |
| Isotopes: 23 whose half-lives are known, with mass numbers 65 to 87. Of these, only one is stable: 75As. | |
