Arsenic

germanium – arsenic – selenium P Ar Sb       Full table
General
Name, Symbol, Number	arsenic, As, 33
Series	metalloids
Group, Period, Block	15 (VA), 4, p
Density, Hardness	5727 kg/m3, 3.5
Appearance	metallic grey
Atomic properties
Atomic weight	74.92160 amu
Atomic radius (calc.)	115 (114) pm
Covalent radius	119 pm
van der Waals radius	185 pm
Electron configuration	[Ar]3d10 4s2 4p3
e- 's per energy level	2, 8, 18, 5
Oxidation states (Oxide)	+-3,5 (mildly acidic)
Crystal structure	rhombohedral
Physical properties
State of matter	solid
Melting point	1090 K (1503 °F)
Boiling point	887 K (1137 °F)
Molar volume	12.95 ×10-6 m3/mol
Heat of vaporization	34.76 kJ/mol
Heat of fusion	369.9 kJ/mol
Vapor pressure	__ Pa at __ K
Speed of sound	__ m/s at __ K
Miscellaneous
Electronegativity	2.18 (Pauling scale)
Specific heat capacity	330 J/(kg*K)
Electrical conductivity	3.45 106/(m·ohm)
Thermal conductivity	50 W/(m*K)
1st ionization potential	947.0 kJ/mol
2nd ionization potential	1798 kJ/mol
3rd ionization potential	2735 kJ/mol
4th ionization potential	4837 kJ/mol
5th ionization potential	6043 kJ/mol
6th ionization potential	12310 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP 75As 100% As is stable with 42 neutrons
SI units & STP are used except where noted.

Arsenic is a chemical element in the periodic table that has the symbol As and atomic number 33. This is a notorious poisonous metalloid that has three allotropic forms; yellow, black and grey. Arsenic and its compounds are used as pesticides, herbicides and insecticides and various alloys.

Notable characteristics

Arsenic is chemically very similar to its predecessor phosphorus, so much so that it will partly substitute for it in biochemical reactions and is thus poisonous. When heated it rapidly oxidizes to arsenous oxide, which has a garlic odor. Arsenic and some arsenic compounds can also sublime upon heating, converting to gaseous form directly. Elemental arsenic is found in two solid forms: yellow and gray/metallic, with specific gravities of 1.97 and 5.73, respectively.

Applications

Lead arsenate has been used, well into the 20th century, as a pesticide on fruit trees (resulting in neurological damage to those working the sprayers), and copper arsenate has even been recorded in the 19th century as a coloring agent in sweets. Other uses;

• Various agricultural insecticides and poisons.
• Gallium arsenide is an important semiconductor material, used in integrated circuits. Circuits made using the compound are much faster (but also much more expensive) than those made in silicon. Unlike silicon it is direct bandgap, and so can be used in is used in laser diodes and LEDs to directly convert electricity into light.
• Arsenic trioxide has been used in hematology to treat patients with acute promyelocytic leukemia that are resistant to ATRA treatment
• Arsenic trioxide is used in Australia for treating termite infestations in houses.
• Also used in; bronzing, pyrotechny

History

The word Arsenic is borrowed from the Persian word زرنيخ Zarnik meaning "yellow orpiment". Zarnik was borrowed by Greek as arsenikon. Arsenic has been known and used in Persia and elsewhere since ancient times. It was frequently used for murder, the symptoms of arsenic poisoning being somewhat ill-defined, until the advent of the Marsh test, a sensitive chemical test for its presence.

During the Bronze Age, arsenic was often included in the bronze (mostly as an impurity), which made the alloy harder.

Albertus Magnus is believed to have been the first to isolate the element in 1250. In 1649 Johann Schroeder published two ways of preparing arsenic.

The alchemical symbol for arsenic is shown opposite.

There is a massive epidemic of arsenic poisoning in Bangladesh. This is due to the massive tube well drinking-water program instigated by western NGOs in the late twentieth century, who failed to test for arsenic in the groundwater. Hundreds of thousands of people are affected. It is thought to be the worst mass-poisoning in history, and possibly the worst environmental disaster in history.

Occurrence

Arsenopyrite also called mispickel (FeSAs) is the most common mineral from which, on heating, the arsenic sublimes leaving ferrous sulfide.

The most important compounds of arsenic are white arsenic, its sulfide, Paris green, calcium arsenate, and lead arsenate. Paris green, calcium arsenate, and lead arsenate have been used as agricultural insecticides and poisons. It is sometimes found native, but usually combined with silver, cobalt, nickel, iron, antimony, or sulfur.

Precautions

Arsenic and many of its compounds are especially potent poisons. Arsenic kills by massively disrupting the digestive system, leading to death from shock. See arsenic poisoning.

Related topics

• Fowler's solution

References