Arsenic

Arsenic, ₃₃As

Arsenic
Pronunciation	/ˈɑːrsənɪk/ (AR-sən-ik) as an adjective: /ɑːrˈsɛnɪk/ (ar-SEN-ik)
Allotropes	grey (most common), yellow, black (see Allotropes of arsenic)
Appearance	metallic grey
Standard atomic weight Ar°(As)
	74.921595(6)
Arsenic in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson P ↑ As ↓ Sb germanium ← arsenic → selenium
Atomic number (Z)	33
Group	group 15 (pnictogens)
Period	period 4
Block	p-block
Electron configuration	[Ar] 3d10 4s2 4p3
Electrons per shell	2, 8, 18, 5
Physical properties
Phase at STP	solid
Sublimation point	887 K ​(615 °C, ​1137 °F)
Density (near r.t.)	5.727 g/cm3
when liquid (at m.p.)	5.22 g/cm3
Triple point	1090 K, ​3628 kPa
Critical point	1673 K, ? MPa
Heat of fusion	grey: 24.44 kJ/mol
Heat of vaporization	34.76 kJ/mol (?)
Molar heat capacity	24.64 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 553 596 646 706 781 874
Atomic properties
Oxidation states	−3, −2, −1, 0, +1, +2, +3, +4, +5 (a mildly acidic oxide)
Electronegativity	Pauling scale: 2.18
Ionization energies	1st: 947.0 kJ/mol 2nd: 1798 kJ/mol 3rd: 2735 kJ/mol (more)
Atomic radius	empirical: 119 pm
Covalent radius	119±4 pm
Van der Waals radius	185 pm
Spectral lines of arsenic
Other properties
Natural occurrence	primordial
Crystal structure	​rhombohedral
Thermal expansion	5.6 µm/(m⋅K) (at r.t.)
Thermal conductivity	50.2 W/(m⋅K)
Electrical resistivity	333 nΩ⋅m (at 20 °C)
Magnetic ordering	diamagnetic
Molar magnetic susceptibility	−5.5×10−6 cm3/mol
Young's modulus	8 GPa
Bulk modulus	22 GPa
Mohs hardness	3.5
Brinell hardness	1440 MPa
CAS Number	7440-38-2
History
Discovery	Arabic alchemists (before AD 815)
Isotopes of arsenic v e
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 73As synth 80.3 d ε 73Ge γ – 74As synth 17.8 d ε 74Ge β+ 74Ge γ – β− 74Se 75As 100% stable
Category: Arsenic view talk edit | references

Arsenic is chemical element 33 on the periodic table. Its symbol is As. Its atomic number is 33 and its atomic mass is 74.92. It is a toxic metalloid. It is in the pnictogen group on the periodic table.

Properties

Chemical properties

Arsenic is a relatively chemically inert element, similar to copper in reactivity. It burns in air to make garlic-smelling arsenic trioxide. Arsenic, as well as some of its compounds, do not have a liquid state; they sublime. Arsenic reacts with fluorine to make arsenic pentafluoride. It reacts with the rest of the halogens to make the arsenic trihalides. Arsenic does not dissolve in hydrochloric acid. It dissolves in concentrated nitric acid to make arsenic acid and in dilute nitric acid to make arsenious acid. It reacts with concentrated sulfuric acid to make arsenic trioxide. Arsenic burns with a pale lavender flame.

Chemical compounds

Arsenic forms chemical compounds in three oxidation states: -3, +3, and +5. -3 compounds are reducing agents. They are the main form of arsenic in the ground (as arsenides). Arsine is a colorless, highly toxic gas with a garlic odor. The +3 state is the most common. They are weak oxidizing agents. Arsenic trioxide is a white solid. It dissolves in water to make a solution of arsenious acid. The arsenic trichlorides are low melting covalent solids. The +5 state is common, too. They are strong oxidizing agents. Arsenic pentafluoride, a colorless and highly reactive gas, is the only stable arsenic pentahalide. Arsenic pentoxide dissolves in water to make arsenic acid, which can make arsenate salts.

-3 compounds

-3 compounds are reducing agents. They are found as arsenides and arsine. The metal arsenides have properties between an alloy and a salt.

• Aluminum arsenide
• Arsenide, the ion
• Arsine, colorless highly toxic flammable gas
• Gallium arsenide, used in LEDs
• Zinc arsenide

+3 compounds

+3 compounds are weak oxidizing agents. Many are colorless, although some are orange.

• Arsenic tribromide, white solid
• Arsenic trichloride, colorless liquid
• Arsenic trifluoride, colorless liquid
• Arsenic triiodide, red-orange solid
• Arsenic trioxide, white solid
• Arsenic trisulfide, yellow solid

Arsenates

Arsenates are salts of arsenious acid.

• Arsenious acid, weak acid
• Arsenate, the ion
• Paris green, copper acetoarsenite (copper acetate arsenite), green solid
• Potassium arsenite
• Sodium arsenate

+5 compounds

+5 compounds are strong oxidizing agents.

• Arsenic pentafluoride, colorless gas
• Arsenic pentoxide, white solid

Arsenates

Arsenates are salts of arsenic acid.

• Arsenate, the ion
• Arsenic acid, white solid or colorless solution
• Lead arsenate
• Potassium arsenate

Occurrence

• 
  Realgar, arsenic sulfide
• 
  Arsenic as an element
• 
  Arsenopyrite, iron arsenic sulfide
• 
  Erythrite, cobalt arsenide

Arsenic is found sometimes as an element in the ground, but is normally found in minerals. Some arsenic minerals have a metal and sulfur along with arsenic. Arsenopyrite is iron arsenic sulfide. It is the same as pyrite with arsenic added. Other arsenic minerals have a metal and arsenic. Erythrite, a cobalt arsenide mineral, is an example. Other arsenic minerals are simple. Realgar and orpiment (arsenic sulfides), simple arsenic minerals, are ores of arsenic.

Arsenic is found as a less toxic variety in fish and mushrooms. Some people think that humans need very small amounts of arsenic to be healthy. Some bacteria can use arsenic instead of phosphorus for some things; they are called arsenic bacteria.

Preparation

Most arsenic is made from the waste products after other metals are processed. Only China actually mines arsenic.

Arsenic is made from arsenopyrite by heating it. This makes arsenic trioxide which sublimes (along with sulfur dioxide), while the iron oxide stays behind. The arsenic trioxide is condensed, while the sulfur dioxide does not condense. The arsenic trioxide can be reduced with carbon. Another way is to heat the arsenopyrite without air. Then gray arsenic is made. Realgar can be heated to make arsenic trioxide as well.

History

Arsenic was known since antiquity. It was alloyed with bronze to make the bronze harder. Some people used arsenic as make-up, although it was toxic. Arsenic was well known as a poison. Since people used it to kill royalty and it was hard to detect, it was called the "Poison of Kings" and the "King of Poisons". An arsenic compound could have been the first organometallic compound (a metal bonded to an organic compound).

Uses

Arsenic compounds were used as a preservative for wood. Once people saw how toxic arsenic was, they stopped using it to preserve wood. Some feed for animals had arsenic in it to prevent disease. Lead arsenate was used as an insecticide in orchards but damaged the brains of those who put the insecticide on the trees.

Arsenic was used in medicines in the 1700s, 1800s, and 1900s. Arsenic trioxide was used to treat cancer. Very tiny doses of arsenic compounds can act as stimulants. Some arsenic compounds are used as poison gases.

Arsenic as an element is used in alloys. The lead in lead acid batteries has some arsenic in it to make it stronger. Some semiconductors have arsenic in them.

Copper arsenate was used as a coloring for sweets. Paris green, a green pigment having arsenic in it, made many people sick. Some bullets have arsenic in them. Arsenic is sometimes added to brass to prevent the zinc from coming out. Arsenic was used in optical glass but was taken out because it was toxic.

The trioxide was once used as a rat poison.

Safety

Arsenic and its compounds are highly toxic. They are carcinogens. Water near arsenic mines is normally contaminated with arsenic. Wood that was preserved with arsenic compounds can leach arsenic into the soil. Emissions from coke ovens have arsenic in them.

References