BROMINE: HISTORY, STRUCTURE, ELECTRON CONFIGURATION, PROPERTIES, USES - CHEMISTRY - 2025

The bromine is a nonmetallic element belonging to the group of halogens, group 17 (VIIA) of the Periodic Table. Its chemical symbol is Br. It appears as a diatomic molecule, whose atoms are linked by a covalent bond, which is why it is assigned the molecular formula Br ₂.

Unlike fluorine and chlorine, bromine in terrestrial conditions is not a gas but a reddish-brown liquid (image below). It is fuming, and it is together with mercury, the only liquid elements. Below it, the iodine, although it intensifies its color and turns purple, can crystallize into a volatile solid.

Vial with pure liquid bromine. Source: Hi-Res Images of Chemical Elements

Bromine was discovered, independently, in 1825 by Carl Löwig, who was studying under the direction of the German chemist Leopold Gmelin; and in 1826, by the French chemist Antoine-Jérome Balard. However, the publication of Balard's experimental results preceded Löwig's.

Bromine is the 62nd most abundant element on Earth, being distributed in low concentrations throughout the earth's crust. In the sea, the average concentration is 65 ppm. The human body contains 0.0004% bromine, its function not being definitively known.

This element is exploited commercially in brines or places that, due to special conditions, are places of high concentration of salts; for example, the Dead Sea, to which the waters of the neighboring territories converge, saturated with salts.

It is a corrosive element capable of attacking metals, such as platinum and palladium. Dissolved in water, bromine can also exert its corrosive action on human tissues, aggravating the situation because hydrobromic acid can be generated. Regarding its toxicity, it can cause significant damage to organs, such as the liver, kidneys, lungs and stomach.

Bromine is very harmful in the atmosphere, being 40-100 times more destructive to the ozone layer than chlorine. Half of the loss of the ozone layer in Antarctica is produced by reactions related to bromomethyl, a compound used as a fumigant.

It has numerous uses, such as: fire retardant, bleaching agent, surface disinfectant, fuel additive, intermediate in the manufacture of sedative, in the manufacture of organic chemicals, etc.

History

Carl Löwig's work

Bromine was discovered independently and almost simultaneously by Carl Jacob Löwig, a German chemist in 1825, and by Antoine Balard, a French chemist in 1826.

Carl Löwig, a disciple of the German chemist Leopold Gmelin, collected water from a spring in Bad Kreuznach and added chlorine to it; After adding the ether, the liquid mixture was stirred.

Then, the ether was distilled off and concentrated by evaporation. As a result he obtained a reddish brown substance, which was bromine.

Antoine Balard's work

Balard, for his part, used ashes from a brown algae known as fucus and mixed them with brine, extracted from the Montpellier salt flats. Thus he released the bromine by passing chlorine through the aqueous material subjected to extraction, in which the magnesium bromide, MgBr ₂, was present.

Subsequently, the material was distilled in the presence of manganese dioxide and sulfuric acid, producing red vapors that condensed into a dark liquid. Balard thought that it was a new element and called it muride, derived from the Latin word muria, with which the brine was designated.

It has been reported that Balard changed the name from muride to brôme at the suggestion of Anglada or Gay-Lussac, based on the fact that brôme means foul, which defines the smell of the discovered element.

The results were published by Belard in the Annales of Chemie and Physique, before Löwig published his.

Only from 1858, it was possible to produce bromine in significant quantities; The year the Stassfurt salt deposits were discovered and exploited, yielding bromine as a by-product of potash.

Structure and electron configuration of bromine

Molecule

Br2 molecule. Source: Benjah-bmm27.

The image above shows the bromine molecule, Br ₂, with a compact filling pattern. Actually, there is a single covalent bond between the two bromine atoms, Br-Br.

Being a homogeneous and diatomic molecule, it lacks a permanent dipole moment and can only interact with others of the same type by means of London dispersion forces.

This is the reason why its reddish liquid is fuming; in Br ₂ molecules, although relatively heavy, their intermolecular forces hold them loosely together.

Bromine is less electronegative than chlorine, and therefore has a less attractive effect on the electrons in the valence shells. As a result, it requires less energy to travel higher energy levels, absorbing green photons, and reflecting a reddish color.

Crystals

Bromine crystal structure. Source: Ben Mills.

In the gas phase, the Br ₂ molecules separate considerably until there are no efficient interactions between them. However, below its melting point, bromine can freeze into reddish orthorhombic crystals (top image).

Note how the Br ₂ molecules are arranged in such an orderly way that they look like "bromine worms." Here, and at these temperatures (T <-7.2 ° C), the dispersion forces are sufficient so that the vibrations of the molecules do not collapse the crystal immediately; but still, several of them will constantly sublimate.

Valence layer and oxidation states

The electron configuration of bromine is:

3d ¹⁰ 4s ² 4p ⁵

Being 3d ¹⁰ 4s ² 4p ⁵ its valence shell (although the 3d ¹⁰ orbital does not play a leading role in its chemical reactions). The electrons in the 4s and 4p orbitals are the outermost, totaling 7, just one electron away from completing the valence octet.

From this configuration, the possible oxidation states for bromine can be deduced: -1, if it gains an electron to be isoelectronic to krypton; +1, leaving 3d ¹⁰ 4s ² 4p ⁴; +3, +4 and +5, losing all electrons from the 4p orbital (3d ¹⁰ 4s ² 4p ⁰); and +7, leaving no electrons in the 4s orbital (3d ¹⁰ 4s ⁰ 4p ⁰).

Properties

Physical appearance

Dark reddish brown fuming liquid. It is found in nature as a diatomic molecule, with the atoms linked by a covalent bond. Bromine is a liquid denser than water and sinks in it.

Atomic weight

79.904 g / mol.

Atomic number

35.

Odor

A pungent, suffocating and irritating smoke.

Melting point

-7.2 ° C.

Boiling point

58.8 ° C.

Density (Br

3.1028 g / cm ³

Water solubility

33.6 g / L at 25 ° C. The solubility of bromine in water is low and tends to increase with decreasing temperature; behavior similar to that of other gases.

Solubilities

Freely soluble in alcohol, ether, chloroform, carbon tetrachloride, carbon disulfide, and concentrated hydrochloric acid. Soluble in non-polar and some polar solvents such as alcohol, sulfuric acid and in many halogenated solvents.

Triple point

265.9 K at 5.8 kPa.

Critical point

588 K at 10.34 MPa.

Heat of fusion (Br

10.571 kJ / mol.

Heat of vaporization (Br

29.96 kJ / mol.

Molar heat capacity (Br

75.69 kJ / mol.

Vapor pressure

At a temperature of 270 K, 10 kPa.

Auto ignition temperature

Not flammable.

ignition point

113 ° C.

Storage temperature

From 2 to 8 ºC.

Surface tension

40.9 mN / m at 25 ° C.

Odor threshold

0.05 - 3.5 ppm. 0.39 mg / m ³

Refractive index (ηD)

1.6083 at 20 ° C, and 1.6478 at 25 ° C.

Electronegativity

2.96 on the Pauling scale.

Ionization energy

- First level: 1,139.9 kJ / mol.

- Second level: 2,103 kJ / mol.

- Third level: 3,470 kJ / mol.

Atomic radio

120 pm.

Covalent radius

120.3 pm.

Van der Waals radio

185 pm.

Reactivity

It is less reactive than chlorine, but more reactive than iodine. It is an oxidant less strong than chlorine and stronger than iodine. It is also a weaker reducing agent than iodine, but stronger than chlorine.

Chlorine vapor is highly corrosive to many materials and human tissues. Attacks many metallic elements, including platinum and palladium; but it does not attack lead, nickel, magnesium, iron, zinc, and under 300 ºC neither sodium.

The bromine in water undergoes a change and turns into bromide. It can also exist as bromate (BrO ₃ ^-), depending on the pH of the liquid.

Due to its oxidizing action, bromine can induce the release of oxygen free radicals. These are strong oxidants and can cause tissue damage. Also, bromine can spontaneously ignite when combined with potassium, phosphorus, or tin.

Applications

Gasoline additive

Ethylene dibromide was used to remove potential lead deposits from automobile engines. After the combustion of gasoline, which used lead as an additive, the bromine combined with lead to form lead bromide, a volatile gas that was expelled through the tailpipe.

Although bromine removed lead from gasoline, its destructive action on the ozone layer was very powerful, which is why it was discarded for this application.

Pesticides

Methylene or bromomethyl bromide was used as a pesticide to purify soils, especially to eliminate parasitic nematodes, such as hookworm.

However, the use of most of the bromine-containing compounds has been discarded due to their destructive action on the ozone layer.

Mercury emission control

Bromine is used in some plants to reduce the emission of mercury, a very toxic metal.

Photography

Silver bromide, in addition to silver iodide and silver chloride, is used as a light-sensitive compound in photographic emulsions.

Therapeutic actions

Potassium bromide, as well as lithium bromide, were used as general sedatives in the 19th and early 20th centuries. Bromides in the form of simple salts are still used in some countries as anticonvulsants.

However, the United States FDA does not approve the use of bromine for the treatment of any disease today.

Fire retardant

Bromine is transformed by flames into hydrobromic acid, which interferes with the oxidation reaction that occurs during fire, and causes its extinction. Bromine-containing polymers are used to make fire retardant resins.

Food additive

Traces of potassium bromate have been added to the flour to improve cooking.

Reagents and chemical intermediate

Hydrogen bromide is used as a reducing agent and catalyst for organic reactions. Bromine is used as a chemical intermediate in the manufacture of drugs, hydraulic fluids, cooling agents, dehumidifiers, and in hair waving preparations.

It also finds use in the production of well drilling fluids, products for water disinfection, bleaching agents, surface disinfectants, dyes, fuel additives, etc.

Biological action

A study carried out in 2014 indicates that bromine is a necessary cofactor for the biosynthesis of collagen IV, which makes bromine an essential element for animal tissue development. However, there is no information about the consequences of an element deficit.

Where is it located

Bromine is extracted commercially from deep salt mines and brine pits found in the state of Arkansas, and in the Great Salt Lake of Utah, both in the United States. This last brine has a bromine concentration of 0.5%.

To extract the bromine, the chlorine in a hot gaseous state is added to the brine, to oxidize the bromide ions in the solution, collecting the elemental bromine.

The Dead Sea, on the border between Jordan and Israel, is a closed sea that is below sea level, which makes it have a very high concentration of salts.

Bromine and potash are obtained there commercially, by evaporating the high salt water from the Dead Sea. In this sea the bromine concentration can reach 5 g / L.

It is also found in high concentrations in some hot springs. Brominite, for example, is a silver bromide mineral found in Bolivia and Mexico.

Risks

Bromine in liquid state is corrosive to human tissues. But the greatest danger to man comes from bromine fumes and their inhalation.

Breathing in an environment with a bromine concentration of 11–23 mg / m ³ produces severe shocks. A concentration of 30–60 mg / m ³ is extremely harmful. Meanwhile, a concentration of 200 mg can be fatal.

References

1. Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
2. National Center for Biotechnology Information. (2019). Bromine. PubChem Database. CID = 23968. Recovered from: pubchem.ncbi.nlm.nih.gov
3. Ross Rachel. (February 8, 2017). Facts about bromine. Recovered from: livesscience.com
4. Wikipedia. (2019). Borax. Recovered from: en.wikipedia.org
5. Lenntech BV (2019). Bromine. Recovered from: lenntech.com