Arsenic

Crystal structure common to Sb, AsSb and gray As
Trimethylarsine
A large sample of native arsenic
Arsenic output in 2006
Realgar
Alchemical symbol for arsenic
The arsenic labyrinth, part of Botallack Mine, Cornwall
Satirical cartoon by Honoré Daumier of a chemist giving a public demonstration of arsenic, 1841
Roxarsone is a controversial arsenic compound used as a feed ingredient for chickens.
Arsenobetaine
An improved rice cooking approach to maximise arsenic removal while preserving nutrient elements

Chemical element with the symbol As and atomic number 33.

- Arsenic
Crystal structure common to Sb, AsSb and gray As

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Groundwater arsenic contamination areas

Arsenic contamination of groundwater

Groundwater arsenic contamination areas

Arsenic contamination of groundwater is a form of groundwater pollution which is often due to naturally occurring high concentrations of arsenic in deeper levels of groundwater.

An 1889 newspaper advertisement for "arsenic complexion wafers". Arsenic was known to be poisonous especially during the Victorian era.

Arsenic poisoning

An 1889 newspaper advertisement for "arsenic complexion wafers". Arsenic was known to be poisonous especially during the Victorian era.

Arsenic poisoning is a medical condition that occurs due to elevated levels of arsenic in the body.

Copper-germanium alloy pellets, likely ~84% Cu; 16% Ge. When combined with silver the result is a tarnish resistant sterling silver. Also shown are two silver pellets.

Metalloid

Type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals.

Type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals.

Copper-germanium alloy pellets, likely ~84% Cu; 16% Ge. When combined with silver the result is a tarnish resistant sterling silver. Also shown are two silver pellets.
Arsenic trioxide or white arsenic, one of the most toxic and prevalent forms of arsenic. The antileukaemic properties of white arsenic were first reported in 1878.
Optical fibers, usually made of pure silicon dioxide glass, with additives such as boron trioxide or germanium dioxide for increased sensitivity
Archaic blue light signal, fuelled by a mixture of sodium nitrate, sulfur, and (red) arsenic trisulfide
Semiconductor-based electronic components. From left to right: a transistor, an integrated circuit, and an LED. The elements commonly recognised as metalloids find widespread use in such devices, as elemental or compound semiconductor constituents (Si, Ge or GaAs, for example) or as doping agents (B, Sb, Te, for example).
Boron, shown here in the form of its β-rhombohedral phase (its most thermodynamically stable allotrope)
Silicon has a blue-grey metallic lustre.
Germanium is sometimes described as a metal
Arsenic, sealed in a container to prevent tarnishing
Antimony, showing its brilliant lustre
Tellurium, described by Dmitri Mendeleev as forming a transition between metals and nonmetals
Carbon (as graphite). Delocalized valence electrons within the layers of graphite give it a metallic appearance.
High purity aluminium is much softer than its familiar alloys. People who handle it for the first time often ask if it is the real thing.
Grey selenium, being a photoconductor, conducts electricity around 1,000 times better when light falls on it, a property used since the mid-1870s in various light-sensing applications
Iodine crystals, showing a metallic lustre. Iodine is a semiconductor in the direction of its planes, with a band gap of ~1.3 eV. It has an electrical conductivity of 1.7 × 10−8 S•cm−1 at room temperature. This is higher than selenium but lower than boron, the least electrically conducting of the recognised metalloids.
White tin (left) and grey tin (right). Both forms have a metallic appearance.

The six commonly recognised metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium.

An ingot of monocrystalline silicon

Semiconductor

Electrical conductivity value falling between that of a conductor, such as metallic copper, and an insulator, such as glass.

Electrical conductivity value falling between that of a conductor, such as metallic copper, and an insulator, such as glass.

An ingot of monocrystalline silicon
Silicon crystals are the most common semiconducting materials used in microelectronics and photovoltaics.
Karl Ferdinand Braun developed the crystal detector, the first semiconductor device, in 1874.
John Bardeen, William Shockley and Walter Brattain developed the bipolar point-contact transistor in 1947.
Mohamed Atalla developed the surface passivation process in 1957 and the MOS transistor in 1959.
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The conductivity of silicon is increased by adding a small amount (of the order of 1 in 108) of pentavalent (antimony, phosphorus, or arsenic) or trivalent (boron, gallium, indium) atoms.

Triple-junction GaAs cells covering MidSTAR-1

Gallium arsenide

III-V direct band gap semiconductor with a zinc blende crystal structure.

III-V direct band gap semiconductor with a zinc blende crystal structure.

Triple-junction GaAs cells covering MidSTAR-1
Band structure of GaAs. The direct gap of GaAs results in efficient emission of infrared light at 1.424 eV (~870 nm).

Molecular beam epitaxy (MBE) of gallium and arsenic: 4 Ga + → 4 GaAs or 2 Ga + → 2 GaAs

Dark green crystals of nickelocene, sublimed and freshly deposited on a cold finger

Sublimation (phase transition)

Transition of a substance directly from the solid to the gas state, without passing through the liquid state.

Transition of a substance directly from the solid to the gas state, without passing through the liquid state.

Dark green crystals of nickelocene, sublimed and freshly deposited on a cold finger
Comparison of phase diagrams of carbon dioxide (red) and water (blue) showing the carbon dioxide sublimation point (middle-left) at 1 atmosphere. As dry ice is heated, it crosses this point along the bold horizontal line from the solid phase directly into the gaseous phase. Water, on the other hand, passes through a liquid phase at 1 atmosphere.
Dry ice subliming in air
Experimental set up for the sublimation reaction of naphthalene Solid naphthalene sublimes and form the crystal-like structure at the bottom of the watch glass
Solid compound of naphthalene sublimed to form a crystal-like structure on the cool surface.
Camphor subliming in a cold finger. The crude product in the bottom is dark brown; the white purified product on the bottom of the cold finger above is hard to see against the light background.
Crystals of ferrocene after purification by vacuum sublimation

For some substances, such as carbon and arsenic, sublimation is much easier than evaporation from the melt, because the pressure of their triple point is very high, and it is difficult to obtain them as liquids.

Structure of hexagonal (gray) selenium

Selenium

Chemical element with the symbol Se and atomic number 34.

Chemical element with the symbol Se and atomic number 34.

Structure of hexagonal (gray) selenium
Structure of the polymer SeO2: The (pyramidal) Se atoms are yellow.
Native selenium in sandstone, from a uranium mine near Grants, New Mexico
Selenium paradox, selenium at nutritional levels or low concentrations is required for cell homeostasis, playing a role as an anti-oxidant through selenoproteins, thus, act chemo-preventive against cancer. In contrast, supra-nutritional levels or higher concentrations act as pro-oxidant in tumour cells, thus can be exploited as chemo-therapeutic against cancer.
Relationship between survival of juvenile salmon and concentration of selenium in their tissues after 90 days (Chinook salmon ) or 45 days (Atlantic salmon ) exposure to dietary selenium. The 10% lethality level (LC10=1.84 µg/g) was derived by applying the biphasic model of Brain and Cousens to only the Chinook salmon data. The Chinook salmon data comprise two series of dietary treatments, combined here because the effects on survival are indistinguishable.

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.

Prediction of germanium, "?=70" (periodic table 1869)

Germanium

Chemical element with the symbol Ge and atomic number 32.

Chemical element with the symbol Ge and atomic number 32.

Prediction of germanium, "?=70" (periodic table 1869)
Germane is similar to methane.
Nucleophilic addition with an organogermanium compound.
Renierite
A typical single-mode optical fiber. Germanium oxide is a dopant of the core silica (Item 1).
A PET bottle

Although the new element somewhat resembled arsenic and antimony in appearance, the combining ratios in compounds agreed with Mendeleev's predictions for a relative of silicon.

Fuming nitric acid contaminated with yellow nitrogen dioxide

Nitric acid

Inorganic compound with the formula HNO3.

Inorganic compound with the formula HNO3.

Fuming nitric acid contaminated with yellow nitrogen dioxide
Two major resonance representations of HNO3
Nitric acid in a laboratory

Some metalloids and metals give the oxides; for instance, Sn, As, Sb, and Ti are oxidized into SnO2, As2O5, Sb2O5, and TiO2 respectively.

A proposed level crossing at railroad tracks would result in "the worse death trap in Los Angeles", a California traffic engineer warned in 1915, because of the impaired view of the railway by automobile drivers. A viaduct was built instead.

Hazard

Potential source of harm.

Potential source of harm.

A proposed level crossing at railroad tracks would result in "the worse death trap in Los Angeles", a California traffic engineer warned in 1915, because of the impaired view of the railway by automobile drivers. A viaduct was built instead.
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Ukrainian "danger" road sign. Stop for dangers, including traffic accidents, natural disasters or other road obstructions

Some harmful chemicals occur naturally in certain geological formations, such as radon gas or arsenic. Other chemicals include products with commercial uses, such as agricultural and industrial chemicals, as well as products developed for home use. Pesticides, which are normally used to control unwanted insects and plants, may cause a variety of negative effects on non-target organisms. DDT can build up, or bioaccumulate, in birds, resulting in thinner-than-normal eggshells, which can break in the nest. The organochlorine pesticide dieldrin has been linked to Parkinson's disease. Corrosive chemicals like sulfuric acid, which is found in car batteries and research laboratories, can cause severe skin burns. Many other chemicals used in industrial and laboratory settings can cause respiratory, digestive, or nervous system problems if they are inhaled, ingested, or absorbed through the skin. The negative effects of other chemicals, such as alcohol and nicotine, have been well documented.