Bromin atau brom (bahasa Yunani: βρωμος, brómos - berbau pesing), adalah unsur kimia pada tabel periodik yang memiliki simbol Br dan nomor atom 35. Unsur dari deret kimia halogen ini berbentuk cairan berwarna merah pada suhu kamar dan memiliki reaktivitas di antara klor dan yodium. Dalam bentuk cairan, zat ini bersifat korosif terhadap jaringan sel manusia dan uapnya menyebabkan iritasi pada mata dan tenggorokan. Dalam bentuk gas, bromin bersifat toksik.

Bromine (  / ̍ b r oʊ m iː n / BROH -meen or / ̍ b r oʊ m ɨ n / BROH -min; from Greek: βρῶμος, brómos, meaning "stench (of he-goats)")[2] is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826. Elemental bromine is a fuming red-brown liquid at room temperature, corrosive and toxic, with properties between those of chlorine and iodine. Free bromine does not occur in nature, but occurs as colorless soluble crystalline mineral halide salts, analogous to table salt.

Bromine is rarer than about three-quarters of elements in the Earth's crust, however the high solubility of bromide ion has caused its accumulation in the oceans, and commercially the element is easily extracted from brine pools, mostly in the United States, Israel and China. About 556,000 tonnes were produced in 2007, an amount similar to the far more abundant element magnesium.[3]

At high temperatures, organobromine compounds are easily converted to free bromine atoms, a process which acts to terminate free radical chemical chain reactions. This makes such compounds useful fire retardants and this is bromine's primary industrial use, consuming more than half of world production of the element. The same property allows volatile organobromine compounds, under the action of sunlight, to form free bromine atoms in the atmosphere which are highly effective in ozone depletion. This unwanted side-effect has caused many common volatile brominated organics like methyl bromide, a pesticide that was formerly a large industrial bromine consumer, to be abandoned. Remaining uses of bromine compounds are in well-drilling fluids, as an intermediate in manufacture of organic chemicals, and in film photography.

Bromine has no essential function in mammals, though it is preferentially used over chloride by one antiparasitic enzyme in the human immune system. Organobromides are needed and produced enzymatically from bromide by some lower life forms in the sea, particularly algae, and the ash of seaweed was one source of bromine's discovery. As a pharmaceutical, simple bromide ion, Br–, has inhibitory effects on the central nervous system, and bromide salts were once a major medical sedative, before being replaced by shorter-acting drugs. They retain niche uses as antiepileptics.

Physical

Elemental bromine exists as a diatomic molecule, Br2. It is a dense, mobile, slightly transparent reddish-brown liquid, that evaporates easily at standard temperature and pressures to give an orange vapor (its color resembles nitrogen dioxide) that has a strongly disagreeable odor resembling that of chlorine. It is one of only two elements on the periodic table that are liquids at room temperature (mercury is the other, although caesium, gallium, and rubidium melt just above room temperature).

At a pressure of 55 GPa bromine converts to a metal. At 75 GPa it converts to a face centered orthorhombic structure. At 100 GPa it converts to a body centered orthorhombic monoatomic form.[4]

Chemical

Being less reactive than chlorine but more reactive than iodine, bromine reacts vigorously with metals, especially in the presence of water, to give bromide salts. It is also reactive toward most organic compounds, especially upon illumination, conditions that favor the dissociation of the diatomic molecule into bromine radicals:

Br2 2 Br·

It bonds easily with many elements and has a strong bleaching action.

Bromine is slightly soluble in water, but it is highly soluble in organic solvents such as carbon disulfide, carbon tetrachloride, aliphatic alcohols, and acetic acid.

Isotopes

Main article: Isotopes of bromine

Bromine has two stable isotopes, 79Br (50.69 %) and 81Br (49.31%). At least 23 other radioisotopes are known. Many of the bromine isotopes are fission products. Several of the heavier bromine isotopes from fission are delayed neutron emitters. All of the radioactive bromine isotopes are relatively short lived. The longest half-life is the neutron deficient 77Br at 2.376 days. The longest half-life on the neutron rich side is 82Br at 1.471 days. A number of the bromine isotopes exhibit metastable isomers. Stable 79Br exhibits a radioactive isomer, with a half-life of 4.86 seconds. It decays by isomeric transition to the stable ground state.[

History

Bromine was discovered independently by two chemists, Carl Jacob Löwig [6] [7] [8] [9] [10] and Antoine Balard,[11][12] in 1825 and 1826, respectively.[13]

Balard found bromide chemicals in the ash of seaweed from the salt marshes of Montpellier. The seaweed was used to produce iodine, but also contained bromine. Balard distilled the bromine from a solution of seaweed ash saturated with chlorine. The properties of the

resulting substance resembled that of an intermediate of chlorine and iodine; with those results he tried to prove that the substance was iodine monochloride (ICl), but after failing to do so he was sure that he had found a new element and named it muride, derived from the Latin word muria for brine.[12]

Löwig isolated bromine from a mineral water spring from his hometown Bad Kreuznach in 1825. Löwig used a solution of the mineral salt saturated with chlorine and extracted the bromine with diethyl ether. After evaporation of the ether a brown liquid remained. With this liquid as a sample for his work he applied for a position in the laboratory of Leopold Gmelin in Heidelberg. The publication of the results was delayed and Balard published his results first.[10]

After the French chemists Louis Nicolas Vauquelin, Louis Jacques Thénard, and Joseph-Louis Gay-Lussac approved the experiments of the young pharmacist Balard, the results were presented at a lecture of the Académie des Sciences and published in Annales de Chimie et Physique.[11] In his publication Balard states that he changed the name from muride to brôme on the proposal of M. Anglada. (Brôme (bromine) derives from the Greek βρωμος (stench).[11]

[14]) Other sources claim that the French chemist and physicist Joseph-Louis Gay-Lussac suggested the name brôme for the characteristic smell of the vapors.[15][16] Bromine was not produced in large quantities until 1860.

The first commercial use, besides some minor medical applications, was the use of bromine for the daguerreotype. In 1840 it was discovered that bromine had some advantages over the previously used iodine vapor to create the light sensitive silver halide layer used for daguerreotypy.[17]

Potassium bromide and sodium bromide were used as anticonvulsants and sedatives in the late 19th and early 20th centuries, until they were gradually superseded by chloral hydrate and then the barbiturates.

OccurrenceSee also: Category:Halide minerals and Halide mineral

World bromine production trend

View of salt evaporation pans on the Dead Sea, where Jordan (right) and Israel (left) produce salt and

bromine 31°9 0″N′ 35°27 0″E′ / 31.15°N 35.45°E

The diatomic element Br2 does not occur naturally. Instead, bromine exists exclusively as bromide salts in diffuse amounts in crustal rock. Owing to leaching, bromide salts have accumulated in sea water at 65 part per million (ppm),[19] which is less than chloride. Bromine may be economically recovered from bromide-rich brine wells and from the Dead Sea waters (up to 50,000 ppm).[20][21] It exists in the Earth's crust at an average concentration of 0.4 ppm, making it the 62nd most abundant element. The bromine concentration in soils varies normally between 5 and 40 ppm, but some volcanic soils can contain up to 500 ppm. The concentration of bromine in the atmosphere is extremely low, at only a few ppt.[22] A large number of organobromine compounds are found in small amounts in nature.

China's bromine reserves are located in the Shandong Province and Israel's bromine reserves are contained in the waters of the Dead Sea. The largest bromine reserve in the United States is located in Columbia County and Union County, Arkansas, U.S.[23]

Production

Bromine production is rather dynamic and has increased sixfold since the 1960s. Approximately 556,000 tonnes (worth around US $2.5 billion) was produced in 2007 worldwide, with the predominant contribution from the United States (226,000 t) and Israel (210,000 t).[3][22][24] US production was excluded from the United States Geological Survey after 2007, and from the 380,000 tonnes mined by other countries in 2010, 140,000 t were produced by China, 130,000 t by Israel and 80,000 t by Jordan.[25]

Bromide-rich brines are treated with chlorine gas, flushing through with air. In this treatment, bromide anions are oxidized to bromine by the chlorine gas.

2 Br− + Cl2 → 2 Cl− + Br2

Laboratory methods of production

In the laboratory, because of its commercial availability and long shelf-life, bromine is not typically prepared. Small amounts of bromine can however be generated through the reaction of solid sodium bromide with concentrated sulfuric acid (H2SO4). The first stage is formation of hydrogen bromide (HBr), which is a gas, but under the reaction conditions some of the HBr is oxidized further by the sulfuric acid to form bromine (Br2) and sulfur dioxide (SO2).

NaBr (s) + H2SO4 (aq) → HBr (aq) + NaHSO4 (aq)

2 HBr (aq) + H2SO4 (aq) → Br2 (g) + SO2 (g) + 2 H2O (l)

Non oxidizing acid alternatives, such as the use of dilute hydrobromic acid with sodium hypobromite, are also available, as the hypobromous acid formed from them is unstable in the presence of bromide, being reduced by it according to the reaction:

2 OBr- (aq) + 4 HBr (aq) → 2Br2 + 2H2O + 2Br-

The reactions are the reverse of disproportionation reactions of elemental bromine in base, and are called comproportionation. A similar reaction happens with sodium hypochlorite, acid, and chloride, leading to elemental chlorine.

Reactions involving an oxidizing agent, such as potassium permanganate or manganese dioxide, on bromide ions in the presence of an acid, also give bromine in the reactions analogous to the formation of elemental chlorine and iodine from an acid and oxidant.

Like iodine, bromine is soluble in chloroform but only slightly soluble in water. In water, the solubility can be increased by the presence of bromide ions. Concentrated solutions of bromine are rarely prepared in the lab because of hazards. As is the case with chlorine solutions or iodine solutions, sodium thiosulphate (or any soluble thiosulphate) is an effective reagent for reducing bromine to colorless odorless bromide, thus dealing with stains and odor from the element in unwanted places. For the same reason, thiosulfate ("fixer's hypo") is used in photography to deal with free bromine in silver bromide film emulsions.

Compounds and chemistry

Organic compounds are brominated by either addition or substitution reactions. Bromine undergoes electrophilic addition to the double-bonds of alkenes, via a cyclic bromonium intermediate. In non-aqueous solvents such as carbon disulfide, this yields the di-bromo product. For example, reaction with ethylene will produce 1,2-dibromoethane. Bromine also undergoes electrophilic addition to phenols and anilines. When used as bromine water, a small amount of the corresponding bromohydrin is formed as well as the dibromo compound. So reliable is the reactivity of bromine that bromine water is employed as a reagent to test for the presence of alkenes, phenols, and anilines. Like the other halogens, bromine participates in free radical reactions. For example, hydrocarbons are brominated upon treatment with bromine in the presence of light.

Bromine, sometimes with a catalytic amount of phosphorus, easily brominates carboxylic acids at the α-position. This method, the Hell-Volhard-Zelinsky reaction, is the basis of the

commercial route to bromoacetic acid. N -Bromosuccinimide is commonly used as a substitute for elemental bromine, being easier to handle, and reacting more mildly and thus more selectively. Organic bromides are often preferable relative to the less reactive chlorides and more expensive iodide-containing reagents. Thus, Grignard and organolithium compound are most often generated from the corresponding bromides.

Certain bromine-related compounds have been evaluated to have an ozone depletion potential or bioaccumulate in living organisms. As a result, many industrial bromine compounds are no longer manufactured, are being restricted, or scheduled for phasing out. The Montreal Protocol mentions several organobromine compounds for this phase out.

Inorganic chemistry

See also: Category:Bromine compounds

Inorganic bromine compounds adopt a variety of oxidation states from −1 to +7.[26]

Oxidation statesof bromine

−1 HBr

0 Br2

+1 BrCl

+3 BrF3

+5 BrF5

+5BrO−3

+7BrO−4

Bromine is an oxidizer, and it will oxidize iodide ions to iodine, being itself reduced to bromide:

Br2 + 2 I− → 2 Br− + I2

Bromine will also oxidize metals and metalloids to the corresponding bromides. Anhydrous bromine is less reactive toward many metals than hydrated bromine, however. Dry bromine reacts vigorously with aluminium, titanium, mercury as well as alkaline earths and alkali metals.

Dissolving bromine in alkaline solution gives a mixture of bromide and hypobromite:

Br2 + 2 OH− → Br− + OBr− + H2O

This hypobromite is responsible for the bleaching abilities of bromide solutions. Warming of these solutions causes the disproportion reaction of the hypobromite to give bromate, a strong oxidising agent very similar to chlorate.

3 BrO− → BrO−

3 + 2 Br−

In contrast to the route to perchlorates, perbromates are not accessible through electrolysis but only by reacting bromate solutions with fluorine or ozone.

BrO3− + H2O + F2 → BrO−

4 + 2 HF

BrO3− + O3 → BrO−

4 + O2

Bromine reacts violently and explosively with aluminium metal, forming aluminium bromide:

2 Al + 3 Br2 → 2 AlBr3

Bromine reacts with hydrogen in gaseous form and gives hydrogen bromide:

H2 + Br2 → 2HBr

Bromine reacts with alkali metal iodides in a displacement reaction. This reaction forms alkali metal bromides and produces elemental iodine:

2 NaI + Br2 → 2 NaBr + I2

2 KI + Br2 → 2 KBr + I2

Applications

A wide variety of organobromine compounds are used in industry. Some are prepared from bromine and others are prepared from hydrogen bromide, which is obtained by burning hydrogen in bromine.[27]

Illustrative of the addition reaction[28] is the preparation of 1,2-dibromoethane, the organobromine compound produced in the largest amounts:

C2H4 + Br2 → CH2BrCH2Br

Flame retardant

Tetrabromobisphenol A

Brominated flame retardants represent a commodity of growing importance, and represent the largest use of bromine. When the brominated material burns, the flame retardant produces hydrobromic acid which interferes in the radical chain reaction of the oxidation reaction of the fire. The mechanism is that the highly reactive hydrogen oxygen and hydroxy radicals react with hydrobromic acid and form less reactive bromine radicals (free bromine atoms). These also react with radicals in the first to help terminate the reaction.[29][30]

The bromine-containing compounds can be placed in the polymers either during polymerization if a small amount of brominated monomer is added or the bromine containing compound is added after polymerization. Tetrabromobisphenol A can be added to produce polyesters or epoxy resins. Epoxy used in printed circuit boards (PCB) are normally made from flame retardant resins, indicated by the FR in the abbreviation of the products (FR-4 and FR-2. Vinyl bromide can be used in the production of polyethylene, polyvinylchloride or polypropylene. Decabromodiphenyl ether can be added to the final polymers.[31]

Gasoline additive

Ethylene bromide was an additive in gasolines containing lead anti-engine knocking agents. It scavenges lead by forming volatile lead bromide, which is exhausted from the engine. This application accounted for 77% of the bromine use in 1966 in the US. This application has declined since the 1970s due to environmental regulations (see below).[32]

Pesticide

Methyl bromide (bromomethane)

Poisonous methyl bromide was widely used as pesticide to fumigate soil and to fumigate housing, by the tenting method. Ethylene bromide was similarly used.[24] These volatile

organobromine compounds are all now regulated as ozone depletion agents. The Montreal Protocol on Substances that Deplete the Ozone scheduled the phase out for the ozone depleting chemical by 2005, and organobromide pesticides are no longer used (in housing fumagation they have been replaced by such compounds as sulfuryl fluoride, which contain neither the chlorine or bromine organics which harm ozone). Prior to the Montreal protocol in 1991 (for example) an estimated 35,000 tonnes of the chemical were used to control nematodes, fungi, weeds and other soil-borne diseases.[33][34]

Medical and veterinary

Potassium bromide

Main article: potassium bromide

Use. Bromide compounds, especially potassium bromide, were frequently used as general sedatives in the 19th and early 20th century. Bromides in the form of simple salts are still used as anticonvulsants in both veterinary and human medicine, although the latter use varies from country to country. For example, the U.S. Food and Drug Administration (FDA) does not approve bromide for the treatment of any disease, and it was removed from over-the-counter sedative products like Bromo-Seltzer, in 1975.[35] Thus, bromide levels are not routinely measured by medical laboratories in the U.S. However, U.S. veterinary medical diagnostic testing laboratories will measure blood bromide levels on request, as an aid to treatment of epilepsy in dogs.

Toxicity. Long-term use of potassium bromide (or any bromide salt) can lead to bromism. This state of central nervous system depression causes the moderate toxicity of bromide in multi-gram doses for humans and other mammals. The very long half-life of bromide ion in the body (~12 days) also contributes to toxicity from bromide build-up in body fluids. Bromide ingestion may also cause a skin eruption resembling acne.

Other uses

Agarose gel stained with ethidium bromide. Ethidium bromide emits orange light when intercalating DNA and when exposed to UV light.

The bromides of calcium, sodium, and zinc account for a sizable part of the bromine market. These salts form dense solutions in water that are used as drilling fluids sometimes called clear brine fluids.[24][36]

Bromine is also used in the production of brominated vegetable oil, which is used as an emulsifier in many citrus-flavored soft drinks (for example, Mountain Dew). After the introduction in the 1940s the compound was extensively used until the UK and the US limited its use in the mid 1970s and alternative emulsifiers were developed.[37]

Soft drinks containing brominated vegetable oil are still sold in the US (2011).[38]

Tralomethrin

Several dyes, agrichemicals, and pharmaceuticals are organobromine compounds. 1-Bromo-3-chloropropane, 1-bromoethylbenzene, and 1-bromoalkanes are prepared by the antimarkovnikov addition of HBr to alkenes. Ethidium bromide, EtBr, is used as a DNA stain in gel electrophoresis.

High refractive index compounds Bromine, like chlorine, is used in maintenance of swimming pools, especially spas (hot tubs),

where it is generated in situ from a bromide plus hydrogen peroxide. In spas, the high water temperatures render chlorinated water purification and buffering compounds unstable, and bromine compounds may improve the life of the free-halogen antimicrobial.

Water purification compounds, disinfectants and insecticides, such as tralomethrin (C22H19Br4NO3).[24]

Potassium bromide is used in some photographic developers to inhibit the formation of fog (undesired reduction of silver).

Bromine vapor is used as the second step in sensitizing daguerreotype plates to be developed under mercury vapor. Bromine acts as an accelerator to the light sensitivity of the previously iodized plate.

Bromine is also used to reduce mercury pollution from coal-fired power plants. This can be achieved either by treating activated carbon with bromine or by injecting bromine compounds onto the coal prior to combustion.

Bromine can also be artificially substituted for the methyl substituent in the nitrogenous base thymine of DNA, creating the base analog 5-bromouracil. When this base is incorporated into DNA its different hydrogen bonding properties may cause mutation at the site of that base pair. The compound 5-bromouracil is thus an artificial mutagen.[39]

Biological role

Tyrian purple

The chemical structure of 6,6 -dibromoindigo′ , the main component of Tyrian Purple

Bromine has no known essential role in human or mammalian health, but inorganic bromine and organobromine compounds do occur naturally, and some may be of use to higher organisms in dealing with parasites. For example, in the presence of H2O2 formed by the eosinophil, and either chloride or bromide ions, eosinophil peroxidase provides a potent mechanism by which eosinophils kill multicellular parasites (such as, for example, the nematode worms involved in filariasis); and also certain bacteria (such as tuberculosis bacteria). Eosinophil peroxidase is a haloperoxidase that preferentially uses bromide over chloride for this purpose, generating hypobromite (hypobromous acid).[40]

Marine organisms are the main source of organobromine compounds. Over 1600 compounds were identified by 1999. The most abundant one is methyl bromide (CH3Br) with an estimated 56,000 tonnes produced by marine algae each year.[41] The essential oil of the

Hawaiian alga Asparagopsis taxiformis consists of 80% methyl bromide.[42] Most of such organobromine compounds in the sea are made via the action of a unique algal enzyme, vanadium bromoperoxidase.[43] Though this enzyme is the most prolific creator of organic bromides by living organisms, other bromoperoxidases exist in nature that do not use vanadium.

A famous example of a bromine-containing organic compound that has been used by humans since ancient times is the fabric dye Tyrian purple.[22][41][44] The brominated indole indigo dye is produced by a medium-sized predatory sea snail, the marine gastropod Murex brandaris. The organobromine nature of the compound was not discovered until 1909 (see Paul Friedländer).[45]

SafetySee also: List of highly toxic gases

Elemental bromine is toxic and causes burns. As an oxidizing agent, it is incompatible with most organic and inorganic compounds. Care needs to be taken when transporting bromine; it is commonly carried in steel tanks lined with lead, supported by strong metal frames.

When certain ionic compounds containing bromine are mixed with potassium permanganate (KMnO4) and an acidic substance, they will form a pale brown cloud of bromine gas.

6 Br– + 2 MnO4– + 8 H+ → 3 Br2 + 2 MnO2 + 4 H2O

This gas smells like bleach and is very irritating to the mucous membranes. Upon exposure, one should move to fresh air immediately. If symptoms of bromine poisoning arise, medical attention is needed.

BROMIN

Nomor atom (Z) 35Konfigurasi elektron [Ar]3d¹⁰4s²4p⁵Massa atom 80Wujud zat cairWarna Merah kecoklatanTitik beku (0C) -7Titik didih (0C) 59Kerapatan (g/cm3) 3,12Kelarutan dalam air (g/ml) 42Energi pengionan pertama (kJ/mol)

1140

Afinitas elektron (kJ/mol) -325Keelektronegatifan (skala Pauling)

2,8

Potensial reduksi standar (volt) 1,06

 

X2 + 2e- 2X-

Jari-jari atom (pm) 115Jari-jari kovalen (Å) 1,14Jari-jari ion (X-) (Å) 1,82Energi ikatan X-X (kJ/mol) 193

Sejarah

Ditemukan oleh Balard pada tahun 1826, tapi belum dapat dipisahkan secara kuantitatif  hingga 1860. Brom (Yunani: βρωμος, brómos), adalah unsur kimia pada tabel periodik yang memiliki simbol Br dan nomor atom 35. Unsur dari deret kimia halogen ini berbentuk cairan berwarna merah pada suhu kamar dan memiliki reaktivitas di antara klor dan yodium. Dalam bentuk cairan, zat ini bersifat korosif terhadap jaringan sel manusia dan uapnya menyebabkan iritasi pada mata dan tenggorokan. Dalam bentuk gas, brom bersifat toksik.

Sifat-sifat

Brom adalah satu-satunya unsur cair non logam. Sifatnya berat, mudah bergerak, cairan berwarna coklat kemerahan, mudah menguap pada suhu kamar menjadi uap merah dengan bau yang sangat tajam., menyerupai klor, dan memiliki efek iritasi pada mata dan tenggorokan. Brom mudah larut dalam air atau karbon disulfida, membentuk larutan berwarna merah, tidak sekuat klor tapi lebih kuat dari iod. Dapat bersenyawa dengan banyak unsur dan memiliki efek pemutih. Ketika brom tumpah ke kulit, akan menimbulkan rasa yang amat pedih. Brom mengakibatkan bahaya kesehatan yang serius, dan peralatan keselamatan kerja harus diperhatikan selama menanganinya.

Banyak brom yang dihasilkan Amerika Serikat digunakan dalam produksi etilen dibromida, komponen pembuatan bensin bersenyawa timbal yang anti-ketukan. Namun karena timbal dalam bensin merusak lingkungan, berarti hal ini akan mempenngaruhi produksi brom di masa yang akan datang.

Kegunaan

Brom digunakan untuk desinfektan, zat tahan api, senyawa pemurni air, pewarna, obat, pembersih sanitasi, bromida anorganik untuk fotografi (Perak bromida (AgBr)) dan lain-lain. Bromida organik juga sama pentingnya.

Kegunaannya yang lain di antaranya : Natrium bromida (NaBr) sebagai obat penenang saraf, Metil bromida (CH3Br) zat pemadam kebakaran, dan Etilen dibromida (C2H4Br2) ditambahkan pada bensin untuk mengubah Pb menjadi PbBr2 .

BROMIN

Nomor atom (Z) : 35Konfigurasi elektron : [Ar]3d¹⁰4s²4p⁵Massa atom : 80Wujud zat : cairWarna : Merah kecoklatanTitik beku (0C) : -7Titik didih (0C) : 59Kerapatan (g/cm3) : 3,12Kelarutan dalam air (g/ml) : 42Energi pengionan pertama (kJ/mol) : 1140Afinitas elektron (kJ/mol) : -325Keelektronegatifan (skala Pauling) : 2,8Potensial reduksi standar (volt) X2 + 2e- 2X- : 1,06Jari-jari atom (pm) : 115Jari-jari kovalen (Å) : 1,14Jari-jari ion (X-) (Å) : 1,82Energi ikatan X-X (kJ/mol) : 193

1. sejarah brominDitemukan oleh Balard pada tahun 1826, tapi belum dapat dipisahkan secara kuantitatif hingga 1860. Brom (Yunani: βρωμος, brómos), adalah unsur kimia pada tabel periodik yang memiliki simbol Br dan nomor atom 35. Unsur dari deret kimia halogen ini berbentuk cairan berwarna merah pada suhu kamar dan memiliki reaktivitas di antara klor dan yodium. Dalam bentuk cairan, zat ini bersifat korosif terhadap jaringan sel manusia dan uapnya menyebabkan iritasi pada mata dan tenggorokan. Dalam bentuk gas, brom bersifat toksik.

2. Sifat-sifat brominBrom adalah satu-satunya unsur cair non logam. Sifatnya berat, mudah bergerak, cairan berwarna coklat kemerahan, mudah menguap pada suhu kamar menjadi uap merah dengan bau yang sangat tajam., menyerupai klor, dan memiliki efek iritasi pada mata dan tenggorokan. Brom mudah larut dalam air atau karbon disulfida, membentuk larutan berwarna merah, tidak sekuat klor tapi lebih kuat dari iod. Dapat bersenyawa dengan banyak unsur dan memiliki efek pemutih. Ketika brom tumpah ke kulit, akan menimbulkan rasa yang amat pedih. Brom mengakibatkan bahaya kesehatan yang serius, dan peralatan keselamatan kerja harus diperhatikan selama menanganinya.Banyak brom yang dihasilkan Amerika Serikat digunakan dalam produksi etilen dibromida, komponen pembuatan bensin bersenyawa timbal yang anti-ketukan. Namun karena timbal dalam bensin merusak lingkungan, berarti hal ini akan mempenngaruhi produksi brom di masa yang akan datang.

3. Fungsi brominBrom digunakan untuk desinfektan, zat tahan api, senyawa pemurni air, pewarna, obat, pembersih sanitasi, bromida anorganik untuk fotografi (Perak bromida (AgBr)) dan lain-lain. Bromida organik juga sama pentingnya.Kegunaannya yang lain di antaranya : Natrium bromida (NaBr) sebagai obat penenang saraf, Metil bromida (CH3Br) zat pemadam kebakaran, dan Etilen dibromida (C2H4Br2) ditambahkan pada bensin untuk mengubah Pb menjadi PbBr2 .

4. Adisi elektrofilik bromin pada propenaSeperti halnya semua alkena yang lain, propena bereaksi pada suhu biasa dengan bromin cair murni, atau dengan larutan bromin dalam sebuah pelarut organik seperti tetraklorometana. Ikatan rangkap terputus, dan sebuah atom brmin menjadi terikat ke masing-masing atom karbon. Bromin kehilangan warna aslinya (merah-coklat) menjadi cairan tidak berwarna. Untuk reaksi dengan propena, terbentuk 1,2-dibromopropana.

Halogen-halogen lain, kecuali fluor, berperilaku serupa. (Fluor bereaksi eksplosif dengan semua hidrokarbon – termasuk alkena – menghasilkan karbon dan hidrogen fluorida).

5. Mekanisme reaksi antara propena dan brominBromin sebagai sebuah elektrofilBromin adalah sebuah molekul yang sangat “terpolarisasikan” dan ikatan pi dalam propena yang mendekat akan menginduksi sebuah dipol dalam molekul bromin tersebut. Jika anda menggambarkan mekanisme ini dalam ujian, tuliskan kata-kata “dipol terinduksi” di samping molekul bromin.Persamaan sederhana dari mekanisme ini adalah sebagai berikut:

Persamaan mekanisme yang lebih akuratPada tahap pertama reaksi, salah satu dari dua atom bromin menjadi terikat pada kedua atom karbon, dengan muatan positif ditemukan pada atom bromin. Ion bromonium terbentuk.

Ion bromonium selanjutnya diserang dari belakang oleh sebuah ion bromida yang terbentuk pada sebuah reaksi dekat.

Definisi dan Fungsi Daur BiogeokimiaDefinisiBiogeokimia adalah pertukaran atau perubahan yang terus menerus, antara komponen biosfer yang hidup dengan tak hidup.

Dalam suatu ekosistem, materi pada setiap tingkat trofik tidak hilang. Materi berupa unsur-unsur penyusun bahan organik tersebut didaur-ulang. Unsur-unsur tersebut masuk ke dalam komponen biotik melalui udara, tanah, dan air. Daur ulang materi tersebut melibatkan makhluk hidup dan batuan (geofisik) sehingga disebut Daur Biogeokimia.FungsiFungsi Daur Biogeokimia adalah sebagai siklus materi yang mengembalikan semua unsur-unsur kimia yang sudah terpakai oleh semua yang ada di bumi baik komponen biotik maupun komponen abiotik, sehingga kelangsungan hidup di bumi dapat terjaga.

PENIPISAN LAPISAN OZONOzon di lapisan atas (lapisan stratosfer), terbentuk secara alami, dan melindungi bumi. Namun zat kimia buatan manusia telah merusak lapisan tersebut, sehingga menimbulkan penipisan lapisan ozon. Zat kimia itu dikenal dengan ODS (ozone-depleting substances), diantaranya chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, dan methyl chloroform. Zat perusak ozon tersebut sebagian masih digunakan sebagai bahan pendingin (coolants), foaming agents, pemadam kebakaran (fire extinguishers), pelarut (solvents), pestisida (pesticides), dan aerosol propellants.Kloroflorokarbon atau Chlorofluorocarbon (CFC) mengandung klorin (chlorine), florin (fluorine) dan karbon (carbon). CFC ini merupakan aktor utama penipisan lapisan ozon. CFCs sangat stabil di troposfer. CFCs yang paling umum adalah CFC-11, CFC-12, CFC-113, CFC-114, dan CFC-115. Potensi merusak ozon dari CFC tersebut secara berurutan adalah 1, 1, 0.8, 1, dan 0.6.Di udara, zat ODS tersebut terdegradasi dengan sangat lambat. Bentuk utuh mereka dapat bertahan sampai bertahun-tahun dan mereka bergerak melampaui troposfer dan mencapai stratosfer. Di stratosfer, akibat intensitas sinar ultraviolet matahari, mereka pecah, dan melepaskan molekul chlorine dan bromine, yang dapat merusak lapisan ozon. Para peneliti memperkirakan satu atom chlorine dapat merusak 100.000 molekul ozon.Walaupun saat ini zat kimia perusak lapisan ozon telah dikurangi atau dihilangkan penggunaannya, namun penggunaannya di waktu yang lampau masih dapat berdampak pada perusakan lapisan ozon. Penipisan lapisan ozon dapat diteliti dengan menggunakan satelit pengukuran, terutama di atas kutub bumi. Penipisan lapisan ozon pelindung akan meningkatkan jumlah radiasi matahari ke bumi yang dapat menyebabkan banyak kasus kanker kulit, katarak, dan pelemahan sistem daya tahan tubuh. Terkena UV berlebihan juga dapat menyebabkan peningkatan penyakit melanoma, kanker kulit yang fatal. Menurut US EPA, sejak 1990, resiko terkena melanoma telah berlipat dua kali.Ultraviolet dapat juga merusak tanaman sensitif, seperti kacang kedelai, dan mengurangi hasil panen. Beberapa penelitian menunjukkan bahwa fitoplankton di laut, yang merupakan basis rantai makanan di laut, telah mengalami tekanan akibat

ultraviolet. Tekanan ini dapat berdampak pada manusia berupa terpengaruhinya pasokan makanan dari laut.