Arsenic: Properties and Uses

Arsenic also represented as As, is an element from the nitrogen group. The element exists in both yellow and gray crystalline forms.

• Arsenic is a natural compound of the earth’s crust and is present at a high level in the groundwater. 
• The element when in its inorganic form is highly toxic. 
• The contaminated water containing inorganic As can cause various health issues. 
• At a higher stage, chronic As poisoning can be caused. 

Key Terms: Arsenic, Nitrogen group, crystalline, inorganic, Arsenic poisoning, electronegativity, thermal conduction 

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What is Arsenic? 

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Arsenic also represented by As belongs to the 4th period and 15th group of the periodic table. The atomic number of the element is 33 and is a metalloid element.

• The electronic configuration of As is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p³ or Ar 3d¹⁰ 4s² 4p³
• The element persists in yellow and gray crystalline form.
• In the periodic table Phosphorus is above As and below it is Antimony. There are some similarities that can be observed between phosphorus and Arsenic. 
• They are the structure of black Arsenic and electronegativity. The three allotropic forms of Arsenic are black, gray, and yellow. 

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Properties of Arsenic 

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The toxic nature of arsenic is already known, some of the other properties of arsenic are given below. 

Physical properties 

The physical properties of Arsenic are as follows: 

• Since it is a metalloid, it exhibits the properties of both metal and non-metal. 
• It is a brittle solid and has low electrical and thermal conductivity.
•  It is solid at 20℃ temperature. 
• The atomic mass of Arsenic is 74.92. 
• The crystalline form of As is rhombohedral. 
• The melting point of As is at 816.8 ℃. 

Chemical properties 

The chemical properties of As are as follows: 

• Arsenic when reacts with moist air, forms arsenic oxide. This oxide forms a black covering on the surface. Arsenic does not have a tendency to react with dry air and also water in the absence of air. The reaction is as below: 

4As_(s) + 5O_2(g) → As₄O_10(s)

4As_(s) + 3O_2(g) → As₄O_6(s)

• The reaction of Arsenic with halogens: When As reacts with fluorine, it forms arsenic pentafluoride which is a colorless compound. 

2As_(s) + 5F_2(g) → 2AsF_5(g) (colorless)

• In a controlled manner, Arsenic can react with other halogens as well. The compound formed when As reacts with Cl, Br and I are arsenic trichloride (colorless), arsenic tribromide (pale yellow), and arsenic triiodide ( red) respectively. The reaction for the same is as follows: 

2As_(s) + 3Cl_2(g) → 2AsCl_3(l) 

2As_(s) + 3Br_2(g) → 2AsBr_3(s)

2As_(s) + 3I_2(g) → 2AsI_3(s)

• When Arsenic reacts with water and oxygen it forms arsenic acid. The reaction is as given below: 

As + 3H₂O + 5O₃ → 2H₃AsO₄ + 5O₂

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Uses of Arsenic 

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Arsenic is used in various fields. Some of the uses of arsenic are as follows: 

• Medicinal: Arsenic was earlier used in medicines but with the increase in the toxicity of As, the medicines are limited now. One of the examples is melarsoprol. There are a lot of side effects of Arsenic. If the person is suffering from promyelocytic leukemia Arsenic trioxide can be used. 
• Military: During world war I, Arsenic is widely used, but its instruments were banned because of its toxicity. 
• Agriculture: They are used as insecticides and fungicides. They can also kill rats. The use of As is also seen in poultry and swine production. Organic Arsenic is less toxic and therefore can be used to promote chickens. 
• Alloys: The most common alloy of As in use is lead. They are used in car batteries. The alloy of As with gallium is widely used as a semiconductor material and also in laser diodes or LEDs. 

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Disadvantages of Arsenic 

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Some of the disadvantages of arsenic are as follows: 

• Arsenic is a toxic element, therefore its use is limited. 
• Upon high dosage, it has killed athletes. 
• The inorganic form of Arsenic is more toxic and is said to be carcinogenic. 
• The consumption of As in water is said to cause many health-related issues and in severe cases can cause arsenic poisoning. 
• The As can affect, the immune system, cardiovascular system, endocrine system, and skin. 

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Things to Remember 

• The atomic number of Arsenic (As) is 33. 
• The electronic configuration can be written as 1s² 2s² 2p⁶ 3s² 3p6 3d¹⁰ 4s² 4p³ or Ar 3d¹⁰ 4s² 4p³
• It is a metalloid, that shows properties of both metal and nonmetal. 
• It has properties similar to Phosphorus. 
• It has three allotropic forms, yellow, black, and gray. 
• The inorganic form of Ar is highly toxic thus reducing its uses. 
• Ar is commonly used in medicine, agriculture, military, and also as alloys. 

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