Bromine

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35 seleniumbrominekrypton
Cl

Br

I
Br-TableImage.png
General
Name, Symbol, Number bromine, Br, 35
Chemical series halogens
Group, Period, Block 17, 4, p
Appearance gas/liquid: red-brown
solid: metallic luster
Br,35.jpg
Atomic mass 79.904(1) g/mol
Electron configuration [Ar] 3d10 4s2 4p5
Electrons per shell 2, 8, 18, 7
Physical properties
Phase liquid
Density (near r.t.) (liquid) 3.1028 g/cm³
Melting point 265.8 K
(-7.3 °C, 19 °F)
Boiling point 332.0 K
(58.8 °C, 137.8 °F)
Critical point 588 K, 10.34 MPa
Heat of fusion (Br2) 10.57 kJ/mol
Heat of vaporization (Br2) 29.96 kJ/mol
Heat capacity (25 °C) (Br2)
75.69 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 185 201 220 244 276 332
Atomic properties
Crystal structure orthorhombic
Oxidation states ±1, 5
(strongly acidic oxide)
Electronegativity 2.96 (Pauling scale)
Ionization energies
(more)
1st: 1139.9 kJ/mol
2nd: 2103 kJ/mol
3rd: 3470 kJ/mol
Atomic radius 115 pm
Atomic radius (calc.) 94 pm
Covalent radius 114 pm
Van der Waals radius 185 pm
Miscellaneous
Magnetic ordering nonmagnetic
Electrical resistivity (20 °C) 7.8×1010 Ω·m
Thermal conductivity (300 K) 0.122 W/(m·K)
Speed of sound (20 °C) ? 206 m/s
CAS registry number 7726-95-6
Notable isotopes
Main article: Isotopes of bromine
iso NA half-life DM DE (MeV) DP
79Br 50.69% Br is stable with 44 neutrons
81Br 49.31% Br is stable with 46 neutrons

Bromine (chemical symbol Br, atomic number 35) is a nonmetal that belongs to a group of chemical elements known as halogens. It is the only liquid nonmetallic element at room temperature and one of five elements that are liquid at or close to room temperature. As a halogen, its reactivity is between that of chlorine and iodine. Liquid bromine is corrosive to human tissue, and inhalation of its vapors irritates and damages the respiratory system. Ingestion of excess bromide can trigger depression and loss of body weight.

Bromine is an important resource for the production of a wide range of consumer goods and materials used for industrial and agricultural applications. For instance, it is used for the manufacture of water purification compounds, fumigants, flame retardants, dyes, pharmaceuticals, sanitizers, and bromide salts for photography. Brominated vegetable oil acts as an emulsifier in various citrus-flavored soft drinks.

Contents

Occurrence

Given its reactivity, bromine is not found as a free element in nature. Instead, it is found in the form of bromide salts in the Earth's crustal rocks and bromide ions in seawater and brine wells.

Approximately 500 million kilograms (worth about $350 million) of bromine are produced per year worldwide (as of 2001), with the United States and Israel being the primary producers. The largest bromine reserve in the United States is located in Columbia and Union Counties in Arkansas.

Discovery

Bromine was discovered at nearly the same time in 1826 by two independent investigators: Antoine Jerome Balard, a French chemist, and Carl Löwig, a student at the University of Heidelberg, Germany. The element, however, was not produced in quantity until 1860. Given the characteristic smell of the vapors, French chemist and physicist Joseph-Louis Gay-Lussac suggested the name bromine, from the Greek word βρωμος (brómos), meaning "stench."

Notable characteristics

In the periodic table, bromine is located in group 17 (former group 7A), the halogen family, between chlorine and iodine. In addition, it lies in period 4, between selenium and krypton. Pure bromine is a heavy, reddish-brown liquid that readily evaporates at ordinary temperature and pressure, forming a red vapor that has a strong, unpleasant odor resembling that of chlorine. The molecular formula of bromine is Br2.

As bromine is a halogen, its chemical properties are similar to those of chlorine, but it is less active than chlorine and more active than iodine. Bromine is slightly soluble in water but highly soluble in carbon disulfide, aliphatic alcohols (such as methanol), and acetic acid. It bonds easily with many elements and has a strong bleaching action.

Bromine is highly reactive and is a powerful oxidizing agent in the presence of water. It reacts vigorously with amines, alkenes, and phenols, as well as aliphatic and aromatic hydrocarbons, ketones, and acids. These organic compounds are brominated by either addition or substitution reactions. With many of the metals and elements, anhydrous (dry) bromine is less reactive than wet bromine; but dry bromine reacts vigorously with aluminum, titanium, mercury, alkaline earth metals and alkali metals.

Bromine does not react with oxygen or nitrogen, but with ozone it forms an unstable compound, bromine(IV) oxide (BrO2). When dissolved in water, it reacts to produce ions of hypobromite (OBr). It also reacts with other halogens—fluorine, chlorine, and iodine—to produce "interhalogen" compounds, including BrF, BrF3, BrF5, ClBr, and BrI.

Safety

Elemental bromine is a strong irritant and, in concentrated form, produces painful blisters on exposed skin and especially mucous membranes. Even low concentrations of bromine vapor (from 10 parts per million) can affect breathing, and inhalation of significant amounts of bromine can seriously damage the respiratory system. Accordingly, one should always wear safety goggles and ensure adequate ventilation when handling bromine.

In addition, bromide salts can be toxic. Ingestion of excess bromide can trigger depression and loss of body weight.

Extraction and recycling

The commercial preparation of bromine involves extracting it from seawater, which contains bromide ions. A batch of seawater is treated with chlorine gas, which oxidizes bromide ions to bromine. At the same time, chlorine is reduced to chloride ions. The reaction can be written as:

2Br + Cl2 → Br2 + 2Cl

Given the high cost of extracting bromine, it is usually recycled rather than disposed of into the environment.

Compounds

A wide range of organic and inorganic compounds contain fluorine. In the case of organic compounds, chemists can replace hydrogen atoms with bromine atoms, thus creating many new products.

The following is a list of inorganic compounds of bromine.

  • Aluminum bromide (AlBr3)
  • ammonium bromide (NH4Br),
  • bromine monofluoride (BrF),
  • bromine pentafluoride (BrF5),
  • bromine trifluoride (BrF3)
  • tetrabromomethane (CBr4)
  • hydrobromic acid (HBr)
  • iron(III) bromide (FeBr3)
  • lithium bromide (LiBr)
  • phosphorus pentabromide (PBr5)
  • phosphorus tribromide (PBr3)
  • potassium bromide (KBr)
  • potassium bromate (KBrO3)
  • silver bromide (AgBr)
  • sodium bromide (NaBr)
  • sodium bromate (NaBrO3)

Applications

Elemental bromine is used to manufacture a wide variety of bromine compounds for industrial and agricultural applications. Traditionally, the largest use of bromine was in the production of 1,2-dibromoethane, which in turn was used as an anti-knock agent for leaded gasolines before they were phased out for environmental reasons.

Bromine continues to be used in the manufacture of fumigants, flame retardants, dyes, pharmaceuticals, water purification compounds, sanitizers, and bromide salts (such as silver bromide) for photography. It is also used to make brominated vegetable oil, which acts as an emulsifier in many citrus-flavored soft drinks.

In the chemical laboratory, bromine is used in tests for alkenes and phenols. When it reacts with an alkene, it loses its orange color and forms a colorless compound (a bromoalkane). When added to phenol, a white precipitate (2,4,6-tribromophenol) is formed. Furthermore, bromine is used to form intermediates in organic synthetic reactions, where it is preferred to iodine because of its much lower cost.

See also

References

External links

All links retrieved March 7, 2013.

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