The Element Bromine
Introduction to Bromine
The element bromine is a dark red liquid with a noxious odor – one of the only two liquids at room temperature on the periodic table. Chemically, it is very reactive, and is never found pure in nature. Bromine is toxic and and corrosive to many living creatures, though it does have commercial applications in water purification, fire-prevention, and pharmaceuticals.
Ten Interesting & Fun Facts about Bromine
- Bromine is one of only two elements to be liquid at room temperature, the other being mercury; it is the only nonmetal to exist as a liquid
- Bromine is actually more abundant in the ocean than it is in the ground
- Up to half of Antarctican ozone loss is due to reactions involving bromine
- Some people use bromine to clean their swimming pools!
- Bromine is one of seven natural diatomic elements, a molecule made of two identical atoms: Br2
- The viscosity of bromine is comparable to that of water
- Commercially, bromine is extracted and isolated from the Dead Sea
- In World War I, soldiers used bromide compounds as a chemical weapons
- Bromine’s name is derived from the Greek word “bromos,” meaning a bad smell, because of its nasty odor
- Since bromine is corrosive, it is often stored in glass or lead-lined containers
Bromine in the Periodic Table
Bromine, element symbol Br, has an atomic number of thirty-five. One can find bromine, a halogen, in the p-block, group 17, particularly in period 4. Bromine is between chlorine and iodine, and has reactivity between the two. Bromine’s electron configuration is [Ar] 3d10 4s2 4p5. Bromine has 7 valence electrons, rendering it a highly electronegative, reactive element, and prone to ionic reactions. On the Pauling Scale, bromine’s electronegativity is 2.96.
Toxicity of Bromine
Bromine is incredibly toxic to living organisms and is absorbable through inhalation, consumption, or physical contact. Bromine attacks and corrodes human tissue. In larger doses, bromine can harm the general nervous system, neurotransmitters, or genetic material. Bromine vapor is also an irritant. Frequent inhalation can lead to a cough, respiratory difficulty, as well as eyes, nose, and throat irritation. “Bromism” is the catch-all term to describe symptoms stemming from constant exposure to bromism. Bromine can be present in small doses in many typical products, such as pesticides, which is why it is crucial to wash fruits and vegetables prior to eating. All in all, it is not difficult to prevent bromine exposure and subsequent toxicity.
Bromine in the Environment
Humans have introduced more bromine into the environment than is naturally occurring, which is harmful to the environment as well as people. When bromine compounds are used in disinfectants in farms or gardens, surface run-off can lead to the accumulation of bromine in natural rivers, ponds, and lakes. Bromine, which does have a natural abundance in saltwater, is hazardous to fish, algae, and other microorganisms. Moreover, organobromo compounds are not bio-degradable, so the inorganic bromine ion will persist. This can lead to bromine overabundance in grasslands and infestation in livestock. The evaporation of bromine in seawater also leads to lower ozone content above the ocean, due to bromine’s (and iodine’s) reactivity with O3.
Bromine Applications in Today’s World
What is Bromine Used For?
Bromine in Pools
Chlorine is commonly known as the primary sanitizing agent in swimming pools, used to kill bacteria, but bromine is actually the major alternative option; though bromine’s natural form is a reddish liquid, it can be found as tablets or granular products. This “Pool Bromine” is not actually bromine in its natural state. Bromine is introduced to pools as part of a salt-oxidizing system, often coupled with sodium, to eventually release hypobromite into the water system. It operates in a higher pH range than chlorine and therefore is often used for sanitization in higher-temperature environments–such as hot tubs and spas–where water pH may fluctuate. Bromine too has a milder scent than chlorine does. However, chlorine works better in sunlight and under UV rays, which inhibit hypobromite formation. Bromine is also more expensive.
Brominated Fire Retardants
The element bromine has fascinating uses in fire prevention. Its large atomic mass and versatility as an organohalogen render it effective in limiting combustion. Thus bromine is added to flame retardants in order to increase their effectiveness, and represent one-fifth of the fire-retardant market. More than 60 different brominated far retardants have existed (and some are restricted due to toxicity). Polybrominated Diphenyl Ethers (PBDEs) and Polybrominated biphenyls (PBBs) are two types that were used in a variety of plastics, textiles, and consumer goods, but have both since been removed from the market. PBDEs were worried to leach chemicals into households, while PBBs were found to increase toxicity in livestock. Hexabromocyclododecanes (HBCDDs) are still used today in thermal insulation. As another example, Tetrabromobisphenol A (TBBPA) brominated fire retardants can be found in thermoplastics and circuitry.
Bromine in Medicine
The element bromine’s medical usage can be traced back to 1835, less than ten years after its discovery when potassium bromide (KBr) was historically used as a sedative. However, bromine’s potential toxicity prevented widespread usage and extreme doses. Today, bromine is still used in pharmaceuticals and as a catalyst for similar manufacturing. Bromine’s ability to dull the nervous system in proper doses makes it ideal to treat epilepsy or others in need of sedation. Furthermore, bromine is also a catalyst in pharmaceutical manufacturing or other medicinal organic reactions, though it does not wind up in the end product.
When and How was Bromine Discovered?
The History of Bromine
Bromine doesn’t have significant applications prior to its discovery in the early nineteenth century. In ancient times, bromine played a role in the coloring of clothing dyes, specifically Tyrian purple, also known as dibromoindigo (6’6 C16H8Br2N2O2). Spiny-dye murex snails retrieved bromine from the ocean and bound it to the indigo molecule on land. Historians believe that both clergy and royalty wore this Tyrian purple color to signify status. Naturally, after bromine’s discovery, bromine had many more scientific and commercial applications.
Who Discovered the Element Bromine
Two scientists– Antoine-Jérôme Balard and Carl Lödwig– discovered bromine independently in 1826 and 1825 respectively. Carl Lödwig discovered bromine by isolating it from a spring of mineral water. He created a solution with chlorine-saturated salt and separated the bromine using diethyl ether. Once the ether completely evaporated, only a reddish-brown liquid remained. Balard discovered bromine in the seaweed of Montpelier salt marshes. Like Lödwig, Balard isolated the bromine by saturating the seaweed solution with chlorine. He realized that the chemical he distilled had properties between chlorine and iodide, and deduced that it must be a new element. Though Balard’s discovery was published first, he and Lödwig are both credited as the discoverers of bromine.
Where is Bromine Present in the Universe?
The element bromine is not an abundant element in nature, and even so, it is never found as a free element. The Earth’s crust is estimated to be 0.00016% bromine; due to natural weathering, bromine from rocks often transition straight to the hydrosphere. Bromine is more particularly concentrated as ions in saltwater, but not as much in freshwater. Likewise, bromine is heavy in some seawater and corals. The largest amounts of bromine can be harvested from the salt deposits, such as the Dead Sea, as well as oil brines, and deepwater reserves. Regarding minerals, bromine is actually found in the silver ores bromargyrite, embrolite, and iodobromite, as it bonds well with silver.
Bromine Chemistry – Compounds, Reactions, Oxidation States
Chemical Properties of Bromine
The element bromine has chemical properties in between chlorine and iodine, the halogens flanking bromine in group 17. Bromine is a very chemically reactive metal and thus is never pure in nature: due to its 7 valence electrons and high electron affinity, bromine reacts readily, and violently, with the alkali metals. It is a strong oxidizing agent, but it does not decompose easily under normal conditions. Bromine is slightly soluble water in a reversible production of hypobromite and is one of few elements with fire-resistant properties. Though bromine does not react with oxygen or nitrogen in the air, it forms a hazardous compound bromine(IV) oxide when reacting with ozone. Bromine additionally reacts with the other halogens.
Bromine Oxidation States
The element bromine exists in the oxidation states -1, 0, +1, +3, +5, and +7. Since bromine is frequently present as bonded to one other atom, -1 is the most common oxidation state for bromine. 0 is the oxidation state for diatomic bromine, +1 is the oxidation state for hypobromite, +3 is the oxidation state for bromite, +5 is the oxidation state for bromate, and +7 is the oxidation state for perbromate.
Bromine is present in a host of both organic and inorganic compounds and can bond in some way with almost every element. The primary exceptions are the noble gases, which are reluctant to engage in any sort of chemical reaction. Bromine can react with all types of metals, nonmetals, and even its fellow halogens!
The vast majority of periodic elements can form a binary compound with the element bromine, known as a bromide. Some notable examples of binary bromides are the following:
- Hydrogen Bromide (HBr): Hydrogen Bromide is an inorganic, colorless gas that is solely made up of hydrogen and bromine. HBr forms hydrobromic acid when dissolved in water, and has many applications in the synthesis of bromine reagents. A variety of chemical and pharmaceutical industries use HBr as a solvent in their processes.
- Silver Bromide (AgBr): Silver Bromide is a light yellow salt that is not soluble in water. Though it can be found as a natural mineral, silver bromide is more frequently produced through laboratory preparation by reacting silver nitrate with an alkaline binary bromide. Since AgBr is light-sensitive, it plays a big role in photography: sodium bromide in gelatin together serve as photograph emulsifiers. AgBr’s light-induced decomposition actually preserves a photograph through its development!
Bromine can form compounds in various configurations with the other halogen elements.
- Iodine Monobromide (IBr): Iodine Monobromide has been identified as either a dark, red-black solid, or dark purple crystals. It is formed by the reaction of its two constituents, iodine and bromine, and serves are the main laboratory source for iodine cation. Iodine mono bromide baths were actually used to relieve joint pain in osteoarthritis patients.
- Bromine Trifluoride (BrF3): Bromine Trifluoride is another inter-halogen compound– a liquid with a strong smell, not-unlike bromine itself. It is used as a fluorinating agent, and so is also used in nuclear fuel preparation; it is part of the production process for UF6, or hex, which assists in uranium enrichment for nuclear reactions and weaponry.
Bromination of Organic Compounds
Bromination is the process of treating a substance with bromine to introduce it into organic compounds. This is the easiest way to begin many synthesis reactions in organic chemistry. UV light will split the diatomic bromine into two bromine radicals–one of the bromines will then go in a chain reaction to react with a hydrogen on the most-substituted carbon; the other bromine will take its place in the molecule. See the example reaction below:
Isolation of the Element Bromine
The element bromine is commercially isolated from seawater. By treating an aqueous solution of bromide anions with chlorine gas, the atoms engage in the oxidation-reduction reaction shown below to produce diatomic bromine and chloride ions. Flushing with products with air then isolates the diatomic bromine.
2Br– + Cl2 → 2Cl– + Br2
Bromine can also be formed in smaller quantities by reacting potassium bromide with sulfuric acid. Since bromine is three times as dense as water, it sinks to the bottom of the flask in the final product.
2KBr + H2SO4 → HBr + KHSO4
2HBr + H2SO4 → SO2 + Br2 + 2H2O
A better way to make bromine in a home or high school laboratory, is to react a mixture of potassium bromide and potassium permanganate or potassium bromate, with sulfuric acid. Copious amounts of bromine (mixed with water) will immediately form. We highly recommend you do not do this indoors, or do it in extremely small quantities.
Physical Properties of Bromine Element
The element bromine is a reddish-brown oil liquid, which is rarely found in its pure form in nature. Its vapor pressure is 168 torr, and it fumes readily.
- Symbol: Br
- Melting point: 19.04 F
- Boiling point: 137.8 F
- Density: 3.119 g/mL
- Atomic weight: 79.904 u
- Atomic number: 35
- Electronegativity: 2.96
- Classification: Halogen, Group 17 Halogen
- Natural abundance: 49.31%
- Electron shell configuration: [Ar] 3d10 4s2
- Isotopes: 79Br and 81Br
Where can I buy Bromine?
Pure bromine is more difficult to come by, and can most easily be found on chemical and equipment distribution sites such as Cole Parmer. Bromine tablets, which contain the bromide ion and are used in pool sanitation, can also be found in most superstores or home-improvement stores, such as Walmart or Home Depot.