SUMMARY / RELATED TOPICS

Arsenic

Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals in combination with sulfur and metals, but as a pure elemental crystal. Arsenic is a metalloid, it has various allotropes, but only the gray form, which has a metallic appearance, is important to industry. The primary use of arsenic is in alloys of lead. Arsenic is a common n-type dopant in semiconductor electronic devices, the optoelectronic compound gallium arsenide is the second most used semiconductor after doped silicon. Arsenic and its compounds the trioxide, are used in the production of pesticides, treated wood products and insecticides; these applications are declining due to the toxicity of its compounds. A few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic are an essential dietary element in rats, goats and other species. A role in human metabolism is not known. However, arsenic poisoning occurs in multicellular life. Arsenic contamination of groundwater is a problem.

The United States' Environmental Protection Agency states that all forms of arsenic are a serious risk to human health. The United States' Agency for Toxic Substances and Disease Registry ranked arsenic as number 1 in its 2001 Priority List of Hazardous Substances at Superfund sites. Arsenic is classified as a Group-A carcinogen; the three most common arsenic allotropes are gray and black arsenic, with gray being the most common. Gray arsenic adopts a double-layered structure consisting of many interlocked, six-membered rings; because of weak bonding between the layers, gray arsenic is brittle and has a low Mohs hardness of 3.5. Nearest and next-nearest neighbors form a distorted octahedral complex, with the three atoms in the same double-layer being closer than the three atoms in the next; this close packing leads to a high density of 5.73 g/cm3. Gray arsenic becomes a semiconductor with a bandgap of 1.2 -- 1.4 eV if amorphized. Gray arsenic is the most stable form. Yellow arsenic is soft and waxy, somewhat similar to tetraphosphorus.

Both have four atoms arranged in a tetrahedral structure in which each atom is bound to each of the other three atoms by a single bond. This unstable allotrope, being molecular, is the most volatile, least dense, most toxic. Solid yellow arsenic is produced by rapid cooling of arsenic vapor, As4, it is transformed into gray arsenic by light. The yellow form has a density of 1.97 g/cm3. Black arsenic is similar in structure to black phosphorus. Black arsenic can be formed by cooling vapor at around 100–220 °C and by crystallization of amorphous arsenic in the presence of mercury vapors, it is brittle. It is a poor electrical conductor. Arsenic occurs in nature as a monoisotopic element, composed of 75As; as of 2003, at least 33 radioisotopes have been synthesized, ranging in atomic mass from 60 to 92. The most stable of these is 73As with a half-life of 80.30 days. All other isotopes have half-lives of under one day, with the exception of 71As, 72As, 74As, 76As, 77As. Isotopes that are lighter than the stable 75As tend to decay by β+ decay, those that are heavier tend to decay by β− decay, with some exceptions.

At least 10 nuclear isomers have been described, ranging in atomic mass from 66 to 84. The most stable of arsenic's isomers is 68mAs with a half-life of 111 seconds. Arsenic has a similar electronegativity and ionization energies to its lighter congener phosphorus and as such forms covalent molecules with most of the nonmetals. Though stable in dry air, arsenic forms a golden-bronze tarnish upon exposure to humidity which becomes a black surface layer; when heated in air, arsenic oxidizes to arsenic trioxide. This odor can be detected on striking arsenide minerals such as arsenopyrite with a hammer, it burns in oxygen to form arsenic trioxide and arsenic pentoxide, which have the same structure as the more well-known phosphorus compounds, in fluorine to give arsenic pentafluoride. Arsenic sublimes upon heating at atmospheric pressure, converting directly to a gaseous form without an intervening liquid state at 887 K; the triple point is 3.63 MPa and 1,090 K. Arsenic makes arsenic acid with concentrated nitric acid, arsenous acid with dilute nitric acid, arsenic trioxide with concentrated sulfuric acid.

Arsenic reacts with metals to form arsenides, though these are not ionic compounds containing the As3− ion as the formation of such an anion would be endothermic and the group 1 arsenides have properties of intermetallic compounds. Like germanium and bromine, which like arsenic succeed the 3d transition series, arsenic is much less stable in the group oxidation state of +5 than its vertical neighbors phosphorus and antimony, hence arsenic pentoxide and arsenic acid are potent oxidizers. Compounds of arsenic resemble in some respects those of phosphorus which occupies the same group of the periodic table; the most common oxidation states for arsenic are: −3 in the arsenides, which are alloy-like intermetallic compounds, +3 in the arsenites, +5 in the arsenates and most organoarsenic compounds. Arsenic bonds to itself as seen in the square As3−4 ions in the mineral skutte

Luck (town), Wisconsin

Luck is a town in Polk County, United States. The population was 881 at the 2000 census; the village of Luck is located within the town. The unincorporated community of West Denmark is located in the town; the unincorporated community of Pole Cat Crossing is located in the town. According to the United States Census Bureau, the town has a total area of 32.7 square miles, of which, 32.1 square miles of it is land and 0.6 square miles of it is water. As of the census of 2000, there were 881 people, 339 households, 251 families residing in the town; the population density was 27.5 people per square mile. There were 400 housing units at an average density of 12.5 per square mile. The racial makeup of the town was 98.07% White, 0.11% Black or African American, 0.45% Native American, 0.34% Asian, 1.02% from two or more races. 0.57 % of the population were Latino of any race. There were 339 households out of which 31.3% had children under the age of 18 living with them, 65.2% were married couples living together, 6.5% had a female householder with no husband present, 25.7% were non-families.

22.4% of all households were made up of individuals and 4.7% had someone living alone, 65 years of age or older. The average household size was 2.60 and the average family size was 3.05. In the town, the population was spread out with 27.7% under the age of 18, 6.7% from 18 to 24, 25.0% from 25 to 44, 28.1% from 45 to 64, 12.5% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 111.3 males. For every 100 females age 18 and over, there were 110.9 males. The median income for a household in the town was $40,417, the median income for a family was $44,659. Males had a median income of $33,571 versus $20,833 for females; the per capita income for the town was $16,096. About 6.2% of families and 9.9% of the population were below the poverty line, including 13.1% of those under age 18 and 4.9% of those age 65 or over. Hans M. Laursen and Wisconsin State Representative, lived in the town

Radio Centraal

Radio Centraal is a Belgian "underground" radio station in the old city center of Antwerp. It began broadcasting on 31 October 1980 as one of the first pirate radio stations which started around the country in protest against the broadcasting monopoly of the national state networks, it always was and still remains an independent radio project with many experimental programmes and niche music. The station is structured as a non-for-profit organisation; the contributors are all volunteers and all the on-air talent finance the investment and cover the running costs of the project. In this way, Radio Centraal can stay independent from local government or commercial sponsors. Most programming is in Dutch; the station offers a starting platform for aspiring and creative radio broadcasters, who are given licence to experiment in sound, music and language. Several have gone on to careers in the Belgian national media. Original founder members such as Jan Balliauw and Stefan Blommaert now work at VRT television as international correspondents.

Since the studio is located close to the Steen on the river front boulevard, Radio Centraal can be said to have its fingers on the pulse of a living city. It has organised and supported many inner city cultural activities, parties and "art" radio projects over the years. Understanding alternative media, Olga Guedes Bailey, Bart Cammaerts, Nico Carpentier, ISBN 0-335-22210-2 Radio Centraal