Properties and Overview of Arsenic

Overview:

Arsenic (As) is a metalloid with the chemical symbol "As" and atomic number 33 on the periodic table. It has a long and complex history, known for its toxic properties and applications in various industries. Arsenic is naturally found in the Earth's crust, typically in minerals such as arsenopyrite, and can also be released into the environment through volcanic activity, erosion, and industrial processes. Arsenic exists in several allotropes, but the most common forms are gray (metallic), yellow, and black arsenic. Gray Arsenic, the most stable and industrially important form, has a metallic appearance and a density of about 5.7 g/cm³. Arsenic is brittle and easily fractures, and it sublimates at a temperature of approximately 600°C without melting at atmospheric pressure. It is a poor conductor of electricity and heat.
Arsenic has a complex chemistry. It readily forms compounds with both metals and non-metals. Common arsenic compounds include arsenic trioxide (As₂O₃), arsenic pentoxide (As₂O₅), and arsenides. Arsenic can react with oxygen, sulfur, and halogens, forming various arsenic oxides, sulfides, and halides. Its ability to bond with other elements gives it diverse chemical behaviour, which is exploited in various industrial applications. Arsenic is well-known for its toxicity, and its exposure can lead to severe health effects. Inorganic arsenic compounds, such as arsenic trioxide, are highly toxic and carcinogenic. Chronic exposure to arsenic, mainly through contaminated water or food, can lead to skin lesions, cancer, cardiovascular diseases, and neurological effects. Acute arsenic poisoning can be fatal, causing symptoms such as vomiting, abdominal pain, and diarrhea, followed by severe systemic effects.
Given its toxicity, the use and handling of arsenic demand stringent safety measures. Personal protective equipment (PPE), proper ventilation, and rigorous industrial hygiene practices are not just recommended, but essential when working with arsenic or its compounds. This is further reinforced by regulations that govern the permissible levels of arsenic in drinking water and food, with strict limits set by agencies like the World Health Organization (WHO) and the U.S. Environmental Protection Agency (EPA).

Production:

Arsenic is typically obtained as a byproduct of the smelting of ores containing lead, copper, gold, and other metals. In these processes, arsenic-bearing ores such as arsenopyrite (FeAsS) are heated in the presence of air, causing the arsenic to oxidize and form arsenic trioxide. This oxide is then collected from flue dust during smelting and can be further refined if needed. China is the largest producer of arsenic and its compounds.

Applications:

Despite its toxicity, arsenic has several critical applications. Historically, it was widely used in pesticides and wood preservatives. However, due to growing environmental and health concerns, this use has significantly declined. Arsenic compounds, particularly arsenic trioxide, are still used in the production of glass and ceramics, where they act as clarifying agents and improve product quality.
In the semiconductor industry, arsenic is used in the form of gallium arsenide (GaAs), a compound with superior electronic properties compared to silicon. It is used in high-speed electronics, light-emitting diodes (LEDs), and solar cells. Arsenic is also used in lead alloys for ammunition, battery grids, and bearing materials, enhancing hardness and corrosion resistance.
Arsenic compounds like arsenic trioxide have been used medicinally to treat acute promyelocytic leukaemia (APL), a rare type of cancer. In this context, arsenic trioxide works by inducing apoptosis (programmed cell death) in cancer cells, although its use is carefully controlled due to its toxicity.

Summary:

Arsenic is a metalloid with a dual nature: it is both a dangerous toxin and a valuable industrial material. Its unique chemical properties enable its use in various applications, from electronics to medicine. However, the risks associated with arsenic require careful management, including strict safety protocols and regulatory oversight, to protect human health and the environment. As technology advances, the challenge remains to harness the beneficial aspects of arsenic while minimizing its harmful effects.

See a comprehensive list of atomic, electrical, mechanical, physical and thermal properties for arsenic below: