Arsenic Atomic Number

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Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. Arsenic appears in three allotropic forms: yellow, black and grey; the stable form is a silver-gray, brittle crystalline solid. It tarnishes rapidly in air, and at high temperatures burns forming a white cloud of arsenic trioxide. Arsenic is a member of group Va of the periodic table, which combines readily with many elements. Atomic Number of Arsenic Arsenic is a chemical element with atomic number 33 which means there are 33 protons and 33 electrons in the atomic structure. The chemical symbol for Arsenic is As. The atom consist of a small but massive nucleus surrounded by a cloud of rapidly moving electrons.


Atomic Number33
Atomic Mass74.9216 atomic mass units
Number of Protons33
Number of Neutrons42
Number of Electrons33
Melting Point817.0° C
Boiling Point613.0° C
Density5.72 grams per cubic centimeter
Normal PhaseSolid
Origin of NameFrom the Greek word 'arsenikos' and the Latin word 'arsenicum,' meaning yellow orpiment
Date and Place of DiscoveryIt's been used since ancient times, but the first recorded use was in 1250 when Albert the Great, an alchemist, heated a compound containing arsenic.
Discovered byAlbert the Great aka Albertus Magnus
Common Compounds
  • Arsenic acid (H3A5O4)
  • Arsenous acid (As(OH)3)
  • Arsenic trisulfide (As2S3), a yellow mineral used as a pigment.
Interesting facts
  • It and all its compounds are poisonous.
  • It can contaminate ground water which is what occurred in Bangladesh (see articles).
Common Uses
  • Poisons, such as insecticides
  • Electrical conduits
  • Semiconductors
  • Bronzing

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Arsenic Atomic StructureElements by NameElements by NumberHome

Arsenic is one of the most ancient element known to human history. It is very toxic and can enter the biological system through contaminated water, soil and air.

History and Discovery

Arsenic Atomic Number And Symbol

Arsenic has a been known since prehistoric time and in the Bronze age it was used to make alloys with bronze. Arsenic was isolated as a distinct compound by Albertus Magnus in 1250. The word arsenic has been originated from zarnik, that means yellow or golden colored in Persian language and from Greek word arsenikon used for male. Later, the Greek word changed to arsenicum in French and finally the English word arsenic was derived from it. Arsenic has a notorious history in regard to its use as a fatal poison and was commonly termed as the poison of the kings and the king of the poisons [1].

Arsenic ion atomic number


Periodic Table ClassificationGroup 15
Period 4
State at 20CSolid
ColorMetallic grey
Electron Configuration[Ar] 3d10 4s2 4p3
Electron Number33
Proton Number33
Electron Shell2, 8, 18, 5
Density5.72 at 20°C
Atomic number23
Atomic Mass74.92 g.mol -1
Electronegativity according to Pauling2.18


Arsenic is abundant element and occurs in about 1.5ppm of concentration in the earth’s crust. It is categorized as the 53rd most abundant element on earth. However, it is also present in minute quantities in water and atmosphere. Arsenic can exist in nature in its free elemental, as well as combined form. In combined form, it is primarily present in minerals of sulfur. There are various allotropic forms of arsenic, black, yellow and gray. The gray allotrope of arsenic is the most common and is widely used all over the world in various applications [2]. Arsenic is metabolized by some bacteria and certain animals, including goats, hamsters and chicken intake arsenic as an essential dietary nutrient. The largest producers of arsenic include China, Russia, Belgium, USA and Morocco.

Physical Characteristics

Yellow arsenic is waxy and soft. Both yellow and gray arsenic are highly volatile and unstable. They have very low density (5.727 g/cm3). Black arsenic is brittle and have a glassy appearance. It is poor conductor of electricity.

Where To Get Arsenic

Chemical Characteristics

When exposed to air it is tarnished and forms a golden-bronze layer on its surface that turns black with passage of time [3]. When arsenic is heated in air, it gives a pungent, garlic like odor as arsenic is oxidized to form arsenic trioxide. Certain compounds of arsenic undergo sublimation when exposed to high temperature, around 614 °C [3]. Arsenic reacts with various metals to form arsenides, and the most common oxidation state of arsenic in compounds is +3 and -3. There are various inorganic compounds of arsenic, including arsenic trioxide which is formed by the oxidation of arsenic in the presence of air and water. Arsenic also readily reacts with halogens to form trihalides and pentahalides, for instance arsenic pentafluoride. There are also many organic compounds of arsenic, such as cacodylic acid, which is formed by the methylation of arsenic trioxide, which is highly pungent and toxic compound.

Significance and Uses

Arsenic Atomic Model

  • The use of arsenic for various products was greatly limited due to the increased knowledge of its toxicity. In 2004, an official ban was applied on the use of chromated copper arsenate (CCA) in US and Europe. CCA was widely used as wood preservative in these countries. However, arsenic is still used in other countries of the world for wood preservation and various other applications.
  • Arsenic is used as a feed additive in swine and poultry industry, to improve the growth of animals.
  • Arsenic is used in various medial purposes, such as drugs for treatment of infection and cancer.
  • Arsenic is used to make alloys with lead to provide strength to lead batteries.

Health Hazards

Arsenic is toxic compound. Its toxicity to biological system and environment is greatly enhanced due to its water solubility. The main source of arsenic toxicity includes weathering of arsenic ores and mineral, and volcanic ash. Traces of arsenic pollution have been found in air, soil and water, from where it can be inhaled and ingested [4]. arsenic water pollution has reached to an alarming level in groundwater in Bangladesh and have according to an estimate, it has affected 57 million people living that region [5].

Isotopes of Arsenic

Natural arsenic has only one stable isotope, arsenic-75 [6]. There are around 33 artificially produced isotopes of arsenic, that range in atomic mass from 60 t0 92. The most stable radioactive isotope is arsenic-73, which as a half-life of 80 days.


[1]. Vahidnia, A.; Van Der Voet, G. B.; De Wolff, F. A. (2007). “Arsenic neurotoxicity – a review”. Human & Experimental Toxicology. 26 (10): 823–32. doi:1177/0960327107084539. PMID18025055.

Arsenic Properties

[2]. Norman, Nicholas C. (1998). Chemistry of Arsenic, Antimony and Bismuth. Springer. p. 50. ISBN978-0-7514-0389-3.

Arsenic Atomic Numbers

[3]. Gokcen, N. A (1989). “The As (arsenic) system”. Bull. Alloy Phase Diagrams. 10: 11–22. doi:10.1007/BF02882166.

[4].Arsenic. The Agency for Toxic Substances and Disease Registry (2009).

Arsenic Atomic Number And Atomic Mass

[5]. Henke, Kevin R. (28 April 2009). Arsenic: Environmental Chemistry, Health Threats and Waste Treatment. p. 317. ISBN978-0-470-02758-5.

Arsenic Atomic Number And Mass

[6]. Georges, Audi; Bersillon, O.; Blachot, J.; Wapstra, A. H. (2003). “The NUBASE Evaluation of Nuclear and Decay Properties”. Nuclear Physics A. Atomic Mass Data Center. 729: 3–128. Bibcode:2003NuPhA.729….3A. doi:10.1016/j.nuclphysa.2003.11.001.

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