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What is Arsenic

Arsenic (pronunciation AR-s’n-ik [2]), represented by the chemical symbol or formula As [1], is a lustrous, tasteless, odorless, brittle metalloid belonging to the family of transition metals [3, 13]. Naturally occurring W is a mixture of 5 isotopes with mass numbers 180, 182, 183, 184 and 186 [1, 3]. Besides that, it has 33 synthetic, radioactive isotopes with known half-lives [3]. In the solid form, it is oxidized by oxygen that turns the surface of the metalloid black. When heated in the gas, it forms arsenious oxide giving off a garlic-like smell [12]. Excepting astatine, it reacts readily with halogens. Though pure As is insoluble in water, many of its compounds dissolve easily in it causing arsenic contamination of drinking water at times that has serious health effects [5].

Arsenic Symbol

Where Is It Found

Only a small amount is found in the uncombined state in nature. Rest is found in minerals, the most common being arsenopyrite. Others are orpiment, enargite and realgar. It is mostly produced as a by-product of lead and copper refining. Some foods, like prawns, contain high levels of the element in an organic, less harmful form. Others foods such as meat, poultry, shellfish, fish, cereals and dairy products may act as dietary sources though they contain arsenic in less toxic levels. It is naturally present in the groundwater of some countries [1, 4].

Arsenic Pictures


Origin of Its Name: Its name is thought to be derived from the Greek word ‘arsenikon’ that is the name for the yellow pigment orpiment [1].

Who Discovered Arsenic: German alchemist, Albertus Magnus [1, 2].

When Was It Discovered: Its discovery year is 1783 [1].

How Was It Discovered

Though arsenic compounds were mined by the early Greek, Chinese and Egyptian civilizations, it is believed that the element itself was first identified by Magnus who stated that it has a metal-like nature.  In the book De Mineralibus, he described how the metalloid could be produced by heating orpiment (As2S3) with soap [1, 2, 3].


Arsenic Identification

Atomic Number  33 [1]
CAS Number  7440-38-2 [1]
Position in the periodic table Group Period Block
  15 [1] 4 [1] p [1]

Location of Arsenic in the Periodic Table

Properties and Characteristics of Arsenic

General Properties

Atomic mass 74.922  atomic mass units [1]
Atomic weight 74.922 [1]
Mass number 75 [3]
Molar mass/molecular weight 74.922 g/mol [6]

Physical Properties

Color/appearance Gray [3]
Melting point/freezing point Sublimes at 616°C, 1141°F [1]
Boiling point Sublimes at 616°C, 1141°F [1]
Density 5.75 g cm-3 [1]
State of matter at room temperature (normal phase) Solid [1]
Hardness (Mohs scale) 3.5 [7]

Chemical Properties

Oxidation state/Oxidation number −3, (+1), +2, +3, +5 [1]
Flammability Yes (As dust) [8]

Magnetic Properties

Magnetic ordering Diamagnetic [9]

Atomic Data of Arsenic (Element 33)

Valence electrons/valency 5 [10]
Quantum numbers
– n 4 [10]
– ℓ 1 [10]
– m 1 [10]
– m s [10]
Electron configuration (noble gas configuration) [Ar] 3d104s24p3 [1]
Crystal structure Trigonal [11]
Atomic structure
– Number of Electrons 33 [3]
– Number of Neutrons 42 [3]
– Number of Protons 33 [3]
Energy levels [3]
– First Energy Level 2
– Second Energy Level 8
– Third Energy Level 18
– Fourth Energy Level 5
Radius of atom
– Atomic Radius 1.85 Å [1]
– Covalent Radius 1.20 Å [1]
Electronegativity (Pauling scale) 2.18  [1]
Ionization energy

(kJmol-1) [1]

1st 2nd 3rd 4th 5th 6th 7th 8th
944.456 1793.585 2735.456 4836.81 6042.88 12311.5

Arsenic Electron Configuration (Bohr Model)

Arsenic Uses

  1. Being a well-known poison, it finds application as insecticides and rat poisons, but their use is highly regulated [1].
  2. It has medicinal applications and may be required by our body in minuscule doses, according to some scientists. The popular cure-all tonic of the Victorian era, Dr. Fowler’s Solution, was nothing but potassium arsenate dissolved in water. These days, organoarsenic compounds are mixed with poultry feed for weight gain and preventing diseases [1].
  3. It is used to dope semiconductors for making solid state It is also used in pyrotechnics, bronzing and for hardening shot [1].
  4. Arsenic compounds are used to preserve wood and make special types of glass [1].

Arsenic Yellow

Is It Dangerous

It is highly toxic in its inorganic form. Arsenic, if present in drinking water, water used for cooking and irrigation can be a health hazard. Long-term exposure can cause skin lesions and cancer. It is also associated with diabetes and cardiovascular disease. Early childhood and uterine exposure can hamper cognitive development and even death [4].

Images of Arsenic Poisoning

Interesting Facts

  • Since our bodies are incapable of absorbing the element itself, pure arsenic is much less hazardous than its compounds [3].
  • It has three distinct allotropes that are in solid form, gray arsenic (the most common one), black arsenic and yellow arsenic [3].

What Does Arsenic Look Like

Arsenic (As Element) Cost

The pure metalloid is priced at $320 for every 100 gram [3].



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