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33
As
74.92
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Arsenious acid - a poison.
| Classification: | Arsenic is a metalloid |
| Atomic weight: | 74.9216 g/mol |
| Density @ 20 oC: | 5.776 g/cm3 |
| Atomic volume: | 12.97 cm3/mol |
Discovery of Arsenic
Arsenic has been known since antiquity in its sulfide compound.
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.
Two methods of preparing arsenic were published by Johann Schroeder in 1649.
The element name is believed to come from the Greek word 'arsenikos' meaning potent.
States
State (s, l, g): solid
Melting point: 1090 K (817 oC)
Melting point: 1090 K (817 oC)
Boiling point: 887 K (614 oC)
Energies
Specific heat capacity: 0.33 J/gK
Heat of fusion: 24.44 kJ mol-1
1st ionization energy: 946.5 kJ mol-1
3rd ionization energy: 2735.4 kJ mol-1
Heat of fusion: 24.44 kJ mol-1
1st ionization energy: 946.5 kJ mol-1
3rd ionization energy: 2735.4 kJ mol-1
Heat of atomization: 303 kJ mol-1
Heat of vaporization (sublimation): 32.4 kJ mol-1
2nd ionization energy: 1797.8 kJ mol-1
Electron affinity: 78 kJ mol-1
Heat of vaporization (sublimation): 32.4 kJ mol-1
2nd ionization energy: 1797.8 kJ mol-1
Electron affinity: 78 kJ mol-1
Oxidation & Electrons
Shells: 2,8,18,5
Minimum oxidation number: -3
Min. common oxidation no.: -3
Electronegativity (Pauling Scale): 2.18
Minimum oxidation number: -3
Min. common oxidation no.: -3
Electronegativity (Pauling Scale): 2.18
Electron configuration: [Ar] 3d10 4s2 4p3
Maximum oxidation number: 5
Max. common oxidation no.: 5
Polarizability volume: 4.3 Å3
Maximum oxidation number: 5
Max. common oxidation no.: 5
Polarizability volume: 4.3 Å3
Appearance & Characteristics
Structure: rhombohedral; layers of 6-member rings
Hardness: 3.5 mohs
Hardness: 3.5 mohs
3d model of arsenic (III) oxide, As2O3. Sometimes called white arsenic, it is colorless, tasteless and was a common poison used by criminals before the development of forensic science.
An old government warning poster.
Color: gray
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.
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 & Compounds
Reaction with air: mild, w/ht ⇒ As4O6
Reaction with 15 M HNO3: mild, w/ht ⇒ H3AsO4, NOx
Oxide(s): As2O3
Hydride(s): AsH3
Reaction with 15 M HNO3: mild, w/ht ⇒ H3AsO4, NOx
Oxide(s): As2O3
Hydride(s): AsH3
Reaction with 6 M HCl: none
Reaction with 6 M NaOH: none
Chloride(s): AsCl3 AsCl5
Reaction with 6 M NaOH: none
Chloride(s): AsCl3 AsCl5
Radius
Atomic radius: 115 pm
Ionic radius (2+ ion): pm
Ionic radius (2- ion): pm
Ionic radius (2+ ion): pm
Ionic radius (2- ion): pm
Ionic radius (1+ ion): pm
Ionic radius (3+ ion): 72 pm
Ionic radius (1- ion): pm
Ionic radius (3+ ion): 72 pm
Ionic radius (1- ion): pm
Conductivity
Thermal conductivity: 50.2 W m-1 K-1
Electrical conductivity: 3.85 x 106 S m-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: Arsenic has 23 isotopes whose half-lives are known, with mass numbers 65 to 87. Of these, only one is stable: 75As.
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: Arsenic has 23 isotopes whose half-lives are known, with mass numbers 65 to 87. Of these, only one is stable: 75As.
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