Arsenic Facts – Element As or 33


Arsenic Facts
Arsenic is a metalloid element with symbol As and atomic number 33.

Arsenic is a chemical element with the symbol As and atomic number 33, making it a part of the pnictogen or nitrogen group in the periodic table. This metalloid element is notorious for its toxicity. Arsenic exhibits a wide range of properties and plays diverse roles in both ancient and modern times.

Discovery and Naming

The discovery of arsenic traces back to ancient times, with references to its use dating as far back as 3000 BC in the form of arsenic sulfides. Arabic alchemists referred to the element at least as early as 815 AD. The element was first identified in its pure form by the German alchemist Albertus Magnus in the 13th century. Its name, “arsenic,” derives from the Greek word “arsenikon,” which means “yellow orpiment,” reflecting one of its common sulfide minerals.

Arsenic Appearance and Allotropes

Arsenic exists in several allotropes, the most common of which are gray, yellow, and black arsenic.

  • Gray arsenic is the most stable and abundant form at room temperature. It appears as a metallic, soft, silvery-gray, brittle solid. While a metalloid, it becomes a semiconductor under specific conditions.
  • Yellow arsenic, also known as α-arsenic, is a more reactive waxy allotrope that is metastable and turns into gray arsenic over time. Yellow arsenic is the most toxic form of the element.
  • Black arsenic, or β-arsenic, is less common and exhibits a shiny, glassy appearance. This allotrope of the element is a poor conductor.

Isotopes

Natural arsenic exists almost exclusively as one stable isotope: arsenic-75. At least 33 radioactive isotopes have been produced for research purposes.

Abundance and Sources

Arsenic is relatively abundant in the Earth’s crust, with an average concentration of about 1.5 ppm. It typically occurs in association with minerals such as arsenopyrite (FeAsS), realgar (As4S4), and orpiment (As2S3). However, it also occurs in relatively pure native form. Natural sources of arsenic include volcanic activity, erosion of arsenic-containing minerals, and human activities such as mining and industrial processes. Top producers of the element are China, Morocco, Russia, and Belgium.

Historical and Current Uses

The history of arsenic’s uses is rich and varied. Historically, it has been employed for medicinal purposes and as a poison, earning its sinister reputation. It was a stimulant tonic for both humans and race horses. In ancient China, arsenic compounds were used in traditional medicine.

In modern times, arsenic has applications in various industries:

  • Agriculture: Arsenic-based pesticides were widely used in the past but have been largely phased out due to their toxicity. Arsenic was a feed additive for poultry and swine until 2015.
  • Alloys: The main use of the element is alloys with lead for car batteries and bullets.
  • Pigments: Paris Green, Scheele’s Green, and Emerald Green are notable arsenic pigments.
  • Semiconductor industry: Arsenic is a dopant in the production of semiconductors.
  • Wood preservation: Arsenic compounds have been used to treat wood to prevent decay.
  • Glass manufacturing: Arsenic trioxide decolorizes glass and increase its clarity.
Electron Levels of an Arsenic Atom

Oxidation States

Arsenic exhibits a range of oxidation states, ranging from -3 to +5. The most common oxidation states -3, +3, and +5.

Biological Role, Health Effects, and Toxicity

Various organisms require arsenic as a trace nutrient, including birds, pigs, and some species of bacteria. However, arsenic has no known biological role in humans and is considered highly toxic. Chronic exposure to arsenic can lead to a variety of health problems, including skin lesions, respiratory issues, and an increased risk of cancer. Inorganic arsenic compounds are particularly toxic, while organic arsenic compounds are less harmful.

Arsenic Poisoning

Arsenic poisoning, also known as arsenicosis or arsenic toxicity, is a medical condition caused by the ingestion, inhalation, or skin contact with high levels of arsenic compounds. Exposure to elevated levels of arsenic leads to a range of symptoms and health problems and is potentially fatal.

Symptoms of Arsenic Poisoning

The symptoms of arsenic poisoning vary depending on the duration and level of exposure. They include:

  • Gastrointestinal Symptoms:
    • Nausea and vomiting
    • Abdominal pain and cramping
    • Diarrhea
    • Loss of appetite
  • Skin Changes:
    • Skin discoloration (hyperpigmentation or hypopigmentation)
    • Skin lesions, rashes, and itching
    • Swelling and blistering
  • Neurological Symptoms:
    • Headaches
    • Confusion
    • Drowsiness
    • Seizures (in severe cases)
  • Respiratory Symptoms:
    • Cough
    • Shortness of breath
    • Sore throat
  • Cardiovascular Symptoms:
    • Abnormal heart rhythm (arrhythmia)
    • Increased risk of heart disease
  • Other Symptoms:
    • Garlic-like breath odor
    • Hair loss
    • Numbness and tingling in extremities (peripheral neuropathy)
    • Abnormal nail growth

Causes of Arsenic Poisoning

Arsenic is an old-school poison, but most people encounter it accidentally:

  • Contaminated Water: One of the most common sources of arsenic exposure is through drinking water that contains high levels of arsenic. Groundwater in certain regions naturally contains elevated levels of arsenic. Industrial processes or agricultural runoff also introduces arsenic into water supplies.
  • Consumption of Contaminated Food: Arsenic accumulates in certain food products, particularly rice, seafood, and poultry. This occurs because the plants and animals absorb arsenic from contaminated soil or water.
  • Industrial Exposure: Workers in industries such as mining, smelting, and pesticide manufacturing are at risk of arsenic exposure through inhalation or skin contact with arsenic-containing materials.
  • Medicinal Use: Historically, arsenic compounds were used in medicines and tonics, which often led to poisoning.

Treatments for Arsenic Poisoning

The treatment for arsenic poisoning depends on the severity of the exposure and the symptoms. Prompt medical intervention is crucial. Treatment options include:

  • Discontinuing Exposure: The first step in treating arsenic poisoning is removing the source of exposure.
  • Chelation Therapy: Severe cases of arsenic poisoning require chelation therapy. Chelating agents like dimercaprol, dimercaptosuccinic acid (DMSA), or dimercaptopropane sulfonate (DMPS) bind to arsenic and help the body eliminate it more rapidly.
  • Supportive Care: Symptomatic treatment includes anti-nausea medications, pain relievers, and treatments for skin rashes.
  • Hydration: Maintaining proper hydration flushes arsenic from the body more effectively.

Table of Key Arsenic Facts

PropertyValue
NameArsenic
SymbolAs
Atomic Number33
Atomic Weight74.9216 g/mol
Group15 (Nitrogen Group or Pnictogens)
Period4
BlockP-block
Electron Configuration[Kr] 4d10 5s2 5p3
Number of Electrons per Shell2, 8, 18, 5
State of Matter at RTSolid
Sublimation Point615°C
Density5.727 g/cm³
Heat of Vaporization34.76 kJ/mol
Heat of Fusion24.44 kJ/mol (gray)
Molar Heat Capacity24.64 J/(mol·K)
Oxidation States-3, -2, -1, 0, +1. +2, +3, +4, +5
Ionization Energies947.0 kJ/mol (first)
Atomic Radius119 pm
Covalent Radius119 pm
Van der Waals Radius185 pm
Crystal StructureRhombohedral
Thermal Conductivity50.2 W/(m·K)
Electrical Resistivity333 nΩ·m
Young’s Modulus8 GPa
Bulk Modulus22 GPa
Mohs Hardness3.5
Magnetic OrderingDiamagnetic

Interesting Arsenic Facts

Here are some interesting facts about the element:

  1. Historical Use in Cosmetics: White arsenic or lead arsenate was ingested or used in cosmetics to achieve a pale complexion.
  2. Napoleon Bonaparte’s Death: There is a theory that suggests Napoleon Bonaparte was exposed to arsenic during his exile on the island of Saint Helena, contributing to his deteriorating health and death.
  3. Arsenic-Eating Bacteria: Some extremophilic bacteria, such as GFAJ-1, thrive in environments with high levels of arsenic. They substitute arsenic for phosphorus in their DNA, challenging the traditional understanding of the biochemistry of life.
  4. Arsenic in Traditional Medicines: Arsenic-based compounds were popular in Ayurvedic and Chinese herbal remedies.
  5. Arsenic’s Role in Taxidermy: Taxidermists used arsenic-based compounds to preserve animal specimens. Modern taxidermy techniques use safer alternatives.
  6. Arsenic in Cigarette Smoke: Cigarette smoke contains trace amounts of arsenic due to the use of arsenic-based pesticides in tobacco farming.
  7. Arsenic as a Semiconductor Dopant: Arsenic is a dopant in the semiconductor industry to introduce n-type conductivity in silicon.
  8. Arsenic in Pressure-Treated Wood: Arsenic-based compounds were a common treatment for outdoor wood products, such as decks and playground equipment, to prevent decay. This practice has been largely discontinued.
  9. Arsenic and Rice: Rice accumulates arsenic from soil and water, making it one of the primary dietary sources of arsenic exposure in some regions. Cooking rice with excess water and rinsing it helps reduce arsenic levels.
  10. Arsenic as a Component in Pigments: Arsenic-based pigments were historically used in paintings and wallpapers.
  11. Arsenic and Pyrotechnics: Arsenic compounds find use in fireworks and pyrotechnics to produce white and yellow flames.
  12. Natural Arsenic Removal: Natural processes, such as microbial activity in groundwater and adsorption onto iron minerals, help reduce arsenic levels in contaminated water sources.

References

  • Grund, Sabina C.; Hanusch, Kunibert; Wolf, Hans Uwe (2008). “Arsenic and Arsenic Compounds”. Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_113.pub2
  • Henke, Kevin R. (2009). Arsenic: Environmental Chemistry, Health Threats and Waste Treatment. John Wiley & Sons. ISBN 978-0-470-02758-5.
  • Seidl, Michael; Balázs, Gábor; Scheer, Manfred (2019). “The Chemistry of Yellow Arsenic”. Chemical Reviews. 119 (14): 8406–8434. doi:10.1021/acs.chemrev.8b00713
  • Uthus, Eric O. (1992). “Evidence for arsenic essentiality”. Environmental Geochemistry and Health. 14 (2): 55–58. doi:10.1007/BF01783629
  • Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. ISBN 0-8493-0464-4.