Bromine Formula: \({\rm{B}}{{\rm{r}}_2}\) Structure, Molar Mass, IUPAC Name

Did you know, the only nonmetal to exist in liquid form at room temperature is Bromine. Bromine is a reddish-brown gas positioned third in the halogen (group \(17\)) of the periodic table. It is the third lightest halogen, with chlorine and iodine as its neighbouring elements. Bromine Formula, also known as Dibromine formula or Brome formula, is a chemical compound that contains bromine.

It has the atomic symbol Br and is a halogen. It emits suffocating vapours and has a pungent odour. It is water-soluble and denser than water. Therefore it sinks in water. It’s poisonous and corrosive. Bromine has an atomic weight of 79.904 and an atomic number of 35. Dibromine was discovered in the year 1825 -1826 by two chemists Antoine Balard and Carl Jacob Lowing. Continue reading to know more.

Bromine Atomic Properties

1. Bromine belongs to group \(17\) and the fourth period of the Periodic Table. Its atomic number is \(35.\)
2. The atomic mass of Bromine is \(79.904\,{\rm{u}}.\)
3. The atomic radius or Van der Waals radius is \(185\,{\rm{pm}}.\)
4. Bromine has the electron configuration \([{\rm{Ar}}]4\;{{\rm{s}}^2}3\;{{\rm{d}}^{10}}4{{\rm{p}}^5}\), with seven electrons in the fourth and outermost shell known as valence electrons. Like all halogens, it is thus one electron short of a full octet and is hence a strong oxidising agent.
5. The Molar mass of Bromine is \(159.8080\;{\rm{g}}/{\rm{mol}}.\)

Physical Properties of Bromine

1. \({\rm{B}}{{\rm{r}}_2}\) or Dibromine is a fuming dark reddish-brown liquid that has a strong pungent smell.
2. \({\rm{B}}{{\rm{r}}_2}\) is denser than water and is also soluble in water. Due to its higher density, bromine sinks in water. Its density is \(3.119\;{\rm{g}}/{\rm{mL}}.\) It dissolves slightly to form oxobromate(I), ({\rm{HOBr}}\) acid and \({\rm{HBr}}.\)
3. The melting and boiling point of this substance is \(- 7.2\,^\circ {\rm{C}}\) and \(58.8\,^\circ {\rm{C}}\) respectively.

Chemical Properties of Bromine

1. Bromine exhibits lower electronegativity and reactivity than chlorine but is higher when compared with iodine \({\rm{ (F: 3}}{\rm{.98, Cl: 3}}{\rm{.16, Br: 2}}{\rm{.96, I: 2}}{\rm{.66) }}.\)
2. Bromine is a weaker oxidising agent than chlorine but a stronger one than iodine. Henceforth, the bromide ion is a weaker reducing agent than the iodide ion but a stronger one than the chloride ion.
3. The density, heats of fusion and evaporation of Bromine are intermediate between those of chlorine and iodine. This is due to the increasing molecular weight of the halogens down the group.
4. Visible light wavelengths absorbed by halogens increase down the group. Hence, halogens darken in colour on descending a group, and Bromine appears reddish-brown.
5. Solid Bromine crystallises in the orthorhombic crystal system, in a layered lattice of \({\rm{B}}{{\rm{r}}_2}\) molecules. The Br–Br distance is \(227\,{\rm{pm}}\) (close to the gaseous Br–Br distance of \(228\,{\rm{pm}}\)).
6. Bromine is a very poor conductor of electricity.
7. Bromine can be made to react directly with hydrogen only by heating or in the presence of a catalyst such as platinum.
8. It reacts moderately with metals and nonmetals.
9. It shows weak bleaching action.
10. Its oxidising action is moderate.
11. Bromine reacts with dilute alkalis to form bromate(I) and bromides, while with concentrated alkalis, it forms bromate(V) and bromides.
12. Bromine always displaces iodine from iodides.

The Bromine Molecule

A bromine molecule or Dibromine is formed when two atoms of Bromine combine to attain stability.

Lewis Structure of Dibromine \(\left( {{\rm{B}}{{\rm{r}}_2}} \right)\)

Lewis Structure depicts the arrangement of an atom’s valence shell electrons. It uses dots and lines to depict electrons and the bonds between atoms. It also gives an insight into the electron configuration of an atom and the way in which it can aim to achieve stability through octet configuration.

Step 1: Calculate the total number of valence electrons.
Bromine lies in the same group as Chlorine and Fluorine and has \(7\) electrons in its valence shell. Hence, for Dibromine, the combined number of valence shell electrons increases to become \(14\).

Step 2: \(\left( {{\rm{B}}{{\rm{r}}_2}} \right)\) is a diatomic molecule, hence, we need to draw \(2\) Bromine atoms adjacent to each other. The two atoms are connected through a chemical bond, represented by a straight line.

Step 3: Two out of \(14\) valence electrons are used in single bond formation. The remaining \(12\) electrons are distributed over the two Br atoms so that both the atoms attain octet configuration.

The Lewis structure of the bromine molecule is shown below.

The bond angle here is \(180\) degrees, as both atoms are in the same element, meaning that the two atoms are precisely opposite to each other.

Molecular Geometry of Dibromine \(\left( {{\rm{B}}{{\rm{r}}_2}} \right)\)

In the case of Dibromine, or \(\left( {{\rm{B}}{{\rm{r}}_2}} \right)\) Both the Bromine atoms have \(7\) electrons in their outermost valence shell and need one more electron to attain stability.

To do so, two Bromine atoms combine to search for the missing electron shell and achieve stability by sharing an electron from each atom.

Dibromine’s molecular geometry is linear and its shape is symmetrical because of the presence of the atoms of the same element.

Hybridisation of Dibromine \(\left( {{\rm{B}}{{\rm{r}}_2}} \right)\)

Hybridisation is the process in which atomic orbitals that are similar in energy level can amalgamate with one another and form new hybrid orbitals that have lesser energy but are more stable.

The general formulae used to calculate the hybridisation of a compound is

Steric number of an atom in a molecule \(=\) No. of sigma bonds \(+\) No. of lone pairs

There are three lone pairs and one sigma bond present on \({\rm{ Br}}\) atom in the \(\left( {{\rm{B}}{{\rm{r}}_2}} \right)\) molecule.

Therefore the hybridisation of \(\left( {{\rm{B}}{{\rm{r}}_2}} \right)\) is \({\bf{s}}{{\bf{p}}^3}\). It has tetrahedral geometry but Its structure is linear due to three lone pairs.

Compounds of Bromine

Silver Bromide

Silver bromide is a pale-yellow solid, which is insoluble in water and in dilute \({\rm{HN}}{{\rm{O}}_3}\). It is sparingly soluble in ammonia solution. In the presence of light, it is reduced to silver.

Hydrogen Bromide

The simplest compound of Bromine is hydrogen bromide, HBr. It is mainly used as a catalyst for many reactions in organic chemistry. Industrially, it is produced by the reaction of hydrogen gas with bromine gas at \(200–400\;\,^\circ {\rm{C}}\) in the presence of a platinum catalyst. In the laboratory, it is produced by the reaction of Bromine with red phosphorus.
\(2{\rm{P}} + 6{{\rm{H}}_2}{\rm{O}} + 3{\rm{B}}{{\rm{r}}_2} \to 6{\rm{HBr}} + 2{{\rm{H}}_3}{\rm{P}}{{\rm{O}}_3}\)
\({{\rm{H}}_3}{\rm{P}}{{\rm{O}}_3} + {{\rm{H}}_2}{\rm{O}} + {\rm{B}}{{\rm{r}}_2} \to 2{\rm{HBr}} + {{\rm{H}}_3}{\rm{P}}{{\rm{O}}_4}\)

Hydrogen bromide is a colourless gas at room temperature, like all the hydrogen halides apart from hydrogen fluoride. The hydrogen of HBr cannot form strong hydrogen bonds to the large and mildly electronegative bromine atom; however, weak hydrogen bonding is present in solid crystalline hydrogen bromide at low temperatures. It is soluble in water and forms a constant boiling acidic mixture. The gas is denser than air.

Bromine Trifluoride

Bromine trifluoride is an interhalogen compound with the formula \({\rm{Br}}{{\rm{F}}_3}\).

It is a straw-coloured liquid with a pungent odour. It is soluble in sulfuric acid but reacts violently with water and organic compounds. It is a powerful fluorinating agent and an ionising inorganic solvent. It is used to produce uranium hexafluoride \(\left( {{\rm{U}}{{\rm{F}}_6}} \right)\) in the processing and reprocessing of nuclear fuel.

\({\rm{Br}}{{\rm{F}}_3}\) is a T-shaped and planar molecule. The bromine centre has two electron pairs. The distance between the bromine centre to each axial fluorine is \(1.81\,\mathop {\rm{A}}\limits^{\rm{o}}\) and to the equatorial fluorine is \(1.72\,\mathop {\rm{A}}\limits^{\rm{o}}.\) The angle between axial fluorine and the equatorial fluorine is slightly smaller than \(90°\) ( it is \(86.2°\)). This is due to the repulsion between the lone pairs on the bromine atom and bond pairs of \({\rm{Br – F}}\) bonds.

Bromine Water formula

Bromine water, also called Bromide bromate solution or Bromine solution, is a brown-red coloured solution with the chemical formula \({{\rm{B}}{{\rm{r}}_2}}\). It is prepared by dissolving diatomic Bromine \(\left( {{\rm{B}}{{\rm{r}}_2}} \right)\) in water \(\left( {{{\rm{H}}_2}{\rm{O}}} \right).\)

The molecular weight of bromine water is \(159.81,\) and the density is \(\left( {1.307\;{\rm{g}}/{\rm{mL}}} \right).\) It has high oxidising properties.

Bromine water is used to identify the functional group present in the organic compound by halogenation mechanism.

Bromine Water Test (Saturation Test)

The bromine water test is a qualitative test, used to distinguish alkenes and alkynes from alkanes. Alkene groups react with bromine water in the dark condition and undergo an additional reaction to give a decolourised solution.

1. Alkane does not react with the bromine water solution, and the brown-red or orange colour of bromine solution remains as such.

Alkene undergoes an electrophilic addition reaction. For example, ethene reacts with bromine water to give \(1,2\) dibromo ethanes.

The reaction takes place at room temperature if the reactants are in the gaseous state (ethene). The colour of the bromine water solution is decolourised as it reacts with ethene.

But, liquid alkenes like cyclohexene react with bromine water solution in the presence of tetrachloromethane.

2. Phenols decolourise bromine water and undergo a substitution reaction to form a brominated compound. A white precipitate of \(2,4,6\)-tribromophenol is formed.

3. Aniline or phenylamine decolourises bromine water to form a white precipitate of \(2,4,6\)-Tribromophenylamine.

4. The bromine water test is used to distinguish between glucose and fructose. With bromine water, glucose undergoes an oxidation reaction to give gluconic acid, whereas fructose fails to undergo any such oxidation reaction.

5. Ketones undergo an electrophilic alpha substitution reaction with bromine water and form a colourless solution of brominated compounds.

6. Aldehyde reacts with bromine water and undergoes an oxidation reaction to give a colourless solution.

Bromine Uses

1. Bromine is used to reduce mercury emissions by up to \(90\) per cent from coal-fired power plants.
2. Bromine is used as a fire retardant, but it is being phased out due to environmental concerns.
3. It is used as a water purifier/disinfectant as an alternative to chlorine.
4. Bromine compounds are used both as soil fumigants in agriculture, particularly fruit-growing and as a fumigant to prevent pests from attacking stored grain and other produce.
5. Brominated substances are essential ingredients of many over-the-counter and prescription medicines.
6. It is used to develop light-sensitive components of photographic emulsion and development.

Summary

The chemical and physical traits of Dibromine can be understood by studying the Lewis structure of the compound.

Further analysis through the \(3\)-dimensional structure lends valuable insights regarding the compound’s physical arrangement, thereby justifying its varied uses in pharmaceuticals, medicines, chemicals, and photography.

FAQs

We have provided some frequently asked questions on Bromine Formula here:

Q.1. Is \({\rm{B}}{{\rm{r}}_2}\) Gas or liquid?
Ans: \({\rm{B}}{{\rm{r}}_2}\) is a reddish-brown coloured element, which is liquid at room temperature.

Q.2. Is Bromine hazardous?
Ans: Bromine is corrosive to human tissue in a liquid state, and its vapours irritate the eyes and throat. Bromine vapours are very toxic with inhalation. Humans can absorb organic bromines through the skin, with food and during breathing.

Q.3. Where is Bromine found in nature?
Ans: Bromine is found naturally in the Earth’s crust and seawater in various chemical forms. It is present in the Earth’s crust in compounds as soluble and insoluble bromides.

Q.4. What is the difference between \({\rm{Br}}\) and \({\rm{B}}{{\rm{r}}_2}\)?
Ans: \({\rm{Br}}\) is the chemical symbol of the bromine atom whereas \({\rm{B}}{{\rm{r}}_2}\) is the molecular symbol of dibromine. As Bromine cannot occur in a state, it is available as a bromine molecule.

Q.5. What is the bromine formula?
Ans: Bromine is a diatomic halogen with the formula \({\rm{B}}{{\rm{r}}_2}\).

Q.6. Why is Bromine written as \({\rm{B}}{{\rm{r}}_2}\)?
Ans: Bromine is found in group \(7\;{\rm{A}}\) of the periodic table, which means it has seven valence electrons. To complete its octet, it only needs to gain one more electron. Hence, it shares one electron with another bromine atom forming a covalent bond. As two atoms are involved in imparting stability to the molecule, it is often written as \({\rm{B}}{{\rm{r}}_2}\).

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