Arsenic, elemental

Arsenic is a metalloid. Solid samples of elemental arsenic (As(0)) tend to be brittle, nonductile, and insoluble in water. These properties largely result from arsenic atoms forming strong covalent bonds with each other. Table 2.3 lists the common chemical and physical properties of arsenic, including its density, electronegativity, and first ionization potential. 

Pararsenolamprite was discovered in a mine in Oita Prefecture, Japan (Matsubara et al., 2001). The Japanese specimens contained antimony and sulfur impurities (As0.96Sb0.03S0.01). In at least the Japanese 

First ionization potential (electron volts, eV) 9.7886 Lide (2007) 

Luster on fresh surface Metallic (rhombohedral form) Nesse (2000) 

Property Elemental (rhombohedral form) Arsenolamprite Pararsenolamprite 

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Arsenic Peroxides. Arsenic peroxides have not been isolated however, elemental arsenic, and a great variety of arsenic compounds, have been found to be effective catalysts ia the epoxidation of olefins by aqueous hydrogen peroxide. Transient peroxoarsenic compounds are beheved to be iavolved ia these systems. Compounds that act as effective epoxidation catalysts iaclude arsenic trioxide, arsenic pentoxide, arsenious acid, arsenic acid, arsenic trichloride, arsenic oxychloride, triphenyl arsiae, phenylarsonic acid, and the arsenates of sodium, ammonium, and bismuth (56). To avoid having to dispose of the toxic residues of these reactions, the arsenic can be immobi1i2ed on a polystyrene resia (57). 

Antimony [7440-36-0J, Sb, belongs to Group 15 (VA) of the periodic table which also includes the elements arsenic and bismuth. It is in the second long period of the table between tin and tellurium. Antimony, which may exhibit a valence of +5, +3, 0, or —3 (see Antimony compounds), is classified as a nonmetal or metalloid, although it has metallic characteristics in the trivalent state. There are two stable antimony isotopes that ate both abundant and have masses of 121 (57.25%) and 123 (42.75%). 

Elemental arsenic normally exists in the a-crystaUine metallic form which is steel-gray in appearance and britde in nature, and in the P-form, a dark-gray amorphous soHd. Other aHotropic forms, ie, yellow, pale reddish-brown to dark brown, have been reported (1), but the evidence supporting some of these aHotropes is meager. MetaUic arsenic, heated under ordinary conditions, does not exhibit a discrete melting point but sublimes. Molten arsenic can be obtained by heating under pressure. 

Elemental arsenic combines with many metals to form arsenides. When heated in the presence of halogens it forms trihaUdes however, pentahaUdes with the exception of AsF (2) and the unstable AsQ. are not readily formed. It reacts with sulfur to form the compounds AS2S2, AsS, As2S, and complex mixtures in various proportions (see Arsenic compounds). 

Arsenic is widely distributed about the earth and has a terrestrial abundance of approximately 5 g/t (4). Over 150 arsenic-bearing minerals are known (1). Table 2 fists the most common minerals. The most important commercial source of arsenic, however, is as a by-product from the treatment of copper, lead, cobalt, and gold ores. The quantity of arsenic usually associated with lead and copper ores may range from a trace to 2 —3%, whereas the gold ores found in Sweden contain 7—11% arsenic. Small quantities of elemental arsenic have been found in a number of localities. 

The commercial uses of arsenic compounds in 1988, measured in terms of elemental arsenic, are wood (qv) preservatives, 69% agricultural products (herbicides (qv) and desiccants (qv)), 23% glass (qv), 4% nonferrous alloys and electronics, 2% and animal feed additives and pharmaceuticals (qv), 2% (see Feeds AND feed additives). Chromated copper arsenate (CCA) [11125-95-4] is the most widely used arsenic-based wood preservative. The Environmental Protection Agency has, however, restricted the use of arsenical wood preservatives to certified appHcators. 

Arsenic tniodide (arsenic(III) iodide), Asl, can be precipitated from a hot solution of trivalent arsenic in hydrochloric acid by the addition of potassium iodide, or it can be formed by treating elemental arsenic with a solution of iodine in carbon disulfide. It is not as easily hydrolyzed as the other arsenic haUdes, but it decomposes slowly in air at 100 °C (rapidly at 200°C) to give a mixture of iodine, arsenic trioxide, and elemental arsenic. Solutions of Asl are unstable, particularly in the presence of moisture. 

The selective epoxidation of ethylene by hydrogen peroxide ia a 1,4-dioxane solvent ia the presence of an arsenic catalyst is claimed. No solvent degradation is observed. Ethylene oxide is the only significant product detected. The catalyst used may be either elemental arsenic, an arsenic compound, or both. 

Derivatives of the Group 15 Elements Arsenic, Antimony, and Bismuth. 

Inorganic elements can be broadly classified as metals and nonmetals. Most metallic elements become toxic at some concentration. Nine elements (arsenic, barium, cadmium, chromium, lead, mercury, nickel, selenium, and thallium) and cyanide are defined as hazardous inorganics for the purposes of deep-well injection. 

Ashe, Arthur J., Ill, and AI-Ahmad, Saleem, Diheteroferrocenes and Related Derivatives of the Group 15 Elements Arsenic, Antimony,... 

The toxicity of arsenicals conforms to the following order, from greatest to least toxicity arsines > inorganic arsenites > organic trivalent compounds (arsenoxides) > inorganic arsenates > organic pentavalent compounds > arsonium compounds > elemental arsenic. 

Solubility in water and body fluids appears to be directly related to toxicity (the low toxicity of elemental arsenic is attributed to its virtual insolubility in water and body fluids, whereas the highly toxic arsenic trioxide, for example, is soluble in water to 12.0 g/L at 0°C, 21.0 g/L at 25°C, and 56.0 g/L at 75°C). 

If the gas is strongly heated it is decomposed and elemental arsenic deposited. 

The honor for discovering the element arsenic in or about 1250 goes to a German alchemist, Albertus Magnus (1193-1280). He was also the first to propose the concepts of afpnitas, which explained how chemicals were held together. In addition, he learned how to separate several compounds into their constituent elements. 

Pesticide wastes that are hazardous by reason of the characteristics are those which are either solvent based and have a flash point <60 °C are aqueous and have a pH <2.0 or >12.5 release HCN or H2S upon contact with acids or leach greater than threshold levels of one or more of the elements arsenic, barium, cadmium, chromium, lead, mercury, selenium and silver, or the pesticides endrin, lindane, methoxychlor, toxa-phene, 2,4-D or 2,4,5-TP. To date, these are the only pesticides for which thresholds have been established. 

Reaction (7.3.16) enriches the GaAs surface with elemental arsenic, resulting in a negative shift in the onset potential as well as an increase in the photocurrent density, which in turn promotes H2 photogeneration [118,119]. The stability of elemental arsenic on a GaAs surface depends on the electrolyte pH, as well as the applied potential. At veiy low pH and a potential of -0.45 V, arsenic is oxidized to stable AS2O3 [120] ... 

Elemental arsenic is stable in dry air but exposure to moist air tarnishes its surface to a golden bronze color which converts to a black oxide on further exposure. Arsenic vapors react with oxygen to form arsenic trioxide (sesquiox-ide) ... 

Elemental arsenic is much less toxic than its soluble compounds. Only its uncommon yellow aUotrope is highly toxic. Inhalation of metal dusts can cause ulceration of nasal septum. Ingestion may produce systemic skin and gastrointestinal effects in humans. Arsenic and its compounds are human carcinogens producing hver tumors. 

When heated in air at 800°C AS4S4 vapors begin to dissociate to AS2S2 which then ignites to form arsenic oxides. Ignition in chlorine produces arsenic chloride. Reaction with fluorine forms arsenic trifluoride. It is stable in water and also in the air at ambient temperatures. It does not react with hot concentrated HCl but is decomposed by nitric acid. It forms thioarsenite ion, AsS3 and elemental arsenic when warmed with caustic soda solution. Similar reaction occurs with sodium sulfide. 

The aqueous solution is highly acidic, pH of 0. IN solution is 1.1. It readily decomposes to arsenic trioxide, elemental arsenic and iodine when heated in air at 200°C. The decomposition, however, commences at 100°C ... 

In this group there is gradation from non-metal to metal. The element arsenic has some of the characteristics of a metal the metallic character becomes more marked in the element antimony, and bismuth is a true metal. All three elements form ammino-salts. 

In the latter, the valency angles must be about 100°, so the layers cannot be flat. Their shape is obtained if, in Figure 38, the atoms shown with the clear circles are displaced somewhat below the plane of the paper and the shaded ones similarly, above it. If the layers formed in this way are then arranged on top of one another, the crystal structure of the elements arsenic, antimony and bismuth are obtained in their normal forms in which they have metallic properties. There also exists a modification of phosphorus with a similar structure. In addition, there are other forms of arsenic and antimony, the properties of which correspond to those of yellow phosphorus these forms contain molecules p As4 and Sb4. 

Other metals such as tin, lead, and thallium may also be methylated as can the elements arsenic and selenium. Thus, the methylation reaction, like acetylation, tends to reduce the water solubility of a foreign compound rather than increase it. 

The irradiated ash sample, with arsenic carrier added, is digested under reflux with hydrochloric, nitric, and perchloric acids. Arsenic (III) is then distilled from the mixture with hydrobromic acid and collected in water. Elemental arsenic is precipitated with sodium hypophosphite, and the activity of the precipitate is counted. The 0.559 MeV y-ray photopeak of 26.5-hr 76As is measured. Radiochemical yields are quantitative. 

Identifying the physical and chemical form of a trace element pollutant at the time of body penetration is probably the single most important prerequisite for meaningful biological testing. It is known, for example, that elemental arsenic (13) and beryllium (46) are nontoxic... 

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