The Ionic Charge, Nuclear Charge, And Reactions of Bromine (Br)

The charge of bromine (Br) influences its ability to enter chemical reactions and form ionic compounds and other chemical compounds. It also influences its applications in various industries.

The charge of an element is an intrinsic property. In that, it is dependent on how the element reacts in a chemical reaction. Bromine naturally forms an anion, a negatively charged ion, when it gets into chemical reactions.

In this article, you will learn about the ionic charge, nuclear charge, Zeff, and reactions of bromine. I also discussed the application of the bromide ion in various industries.

Properties of bromine

  • Bromine is the third element in the halogen series
  • It is a rare element that is present as soluble and insoluble bromine compounds. Bromine is present in ocean water, in thermal springs, in insoluble silver bromide minerals, and in natural salts
  • Bromine, in its free state, is a reddish-brown liquid with a pungent smell. It also irritates the skin, eyes, and respiratory system. However, free bromine is not naturally occurring because of its high reactivity
  • Bromine has an atomic number of 35 and an atomic weight of 79.9 g/mol
  • It is a liquid at STP with a boiling point of 137.8°F (58.8°C) and a melting point of 19°F (-7.2°C)
  • Near its melting point, bromine has a density of 3.1028 g/cm3
  • Bromine has an electronic configuration of 1s22s22p63s23p63d104s24p5 and  can exhibit oxidation states of -1 to +7, except for +6

What is the charge of Br?

The charge of Br is -1. This halogen has seven electrons in its outermost shell. It will gain one more to complete its octet and attain stability. This is its ionic charge.

The ionic charge of an element is a function of how it reacts and forms an ion.

What is the nuclear charge of Br?

The nuclear charge of bromine is the total number of protons in its nucleus, which is 35.

 You can see that this is the same as its atomic number. The nuclear charge of all elements is the same as their atomic number.

What is the effective nuclear charge of Br?

Effective nuclear charge, Zeff, is a difference between the nuclear charge and the shielding constant.

That is, Zeff = Z – S

Where Z is the nuclear charge, 35

S is the shielding constant which will be determined using Slater’s rule.

To determine S, start by writing out the electronic configuration:


The inner electrons in 1s22s22p6 contribute 1 to the shielding constant, electrons in 3s23p63d10 contribute 0.85 to the shielding constant, and electrons in 4s24p5 contribute 0.35

Therefore, (6 x 0.35) + (18 x 0.85) + (10 x 1)

= 2.1 + 15.3 + 10

S = 27.4

Zeff = Z – S

= 35 – 27.4

Zeff = 7.6

What is the oxidation number of Br in BrO3?

The oxidation number of Br in the bromate ion, BrO3, can be determined by substituting the oxidation state of oxygen into the chemical formula. In this anion, the whole compound will be equal to -1, the charge on the anion.

Br + 3(-2) = -1

Br – 6 = -1

Therefore, Br = +5

What are the reactions of bromine?

Reaction with water

The reaction of bromine with water is spontaneous. It involves disproportionation, oxidation, and reduction. The products of this reaction are hypobromous acid (HBrO) and hydrobromic acid (HBr).

It is naturally an equilibrium reaction. However, the pH of the solution can affect the position of the equilibrium.

Br2 + H2O ⇌ HBrO + HBr

Addition reaction/bromine test

Bromine reacts with alkenes to form saturated brominated hydrocarbon compounds. Bromine reacts with alkenes and breaks the double bond to form a bromoalkane. This reaction is used in laboratories to test for unsaturation in hydrocarbons.

The reaction is as follows:

H2C=CH2 + Br2 ———> BrHC=CCHBr

(ethene) (bromine) (1,2-dibromoethane)

Alkynes also undergo addition reaction with alkynes, unsaturated hydrocarbons with triple bonds. They first form bromoalkenes and then bromoalkanes in excess bromine.

C2H2 + Br2 ———> BrHC=CHBr  + Br2 ———> Br2HC-CHBr2

(ethyne) (bromine) (1,2-dibromoethene) (1,1,2,2-tetrabromoethane)

Displacement reactions

Electron affinity decreases down the group, from fluorine to astatine. A more reactive halogen will displace a less reactive halogen from a halide solution. For instance, bromine will displace iodine from a sodium iodide solution.

The reaction is as follows:

2NaI + Br2 ———> 2NaBr + I2

Reaction with ozone

Halogens do not react with oxygen in the air. They rather react with ozone to form bromine dioxide and oxygen gas. This reaction will only occur at -108.4°F (-78°C).

Br2 + 2O3 ———> 2BrO2 + O2

Reaction with metals

Bromine forms metal bromides with metals to form metal bromides in highly exothermic reactions. This reaction is highly violent with highly reactive metals like sodium.

Br2 + 2Na ———> 2NaBr

Reaction with ammonia

Adding bromine to ammonia-rich water results in the formation of bromamines, such as monobromamine (NH2Br), dibromamine (NHBr2), and tribromamine (NBr2).

Bromine is a powerful disinfectant like chlorine that is useful in the treatment of water in pools and cooling towers.

Applications of bromide ion

In water treatment

Bromine-based disinfectants help to inhibit and control microbial growth in pools, spas, and other artificial water bodies. It is the charge on bromine that enhances the formation of these compounds with other chemicals.

Flame retardants

The bromide ion is involved in the synthesis of bromine-based flame retardants. These retardants are useful in the production of textiles, electronics, and construction materials to make them fire-resistant. These bromine-based components can disrupt combustion and inhibit the spread of fire.

Pharmaceutical industries

Bromide ions interact with other elements and chemicals to form complex compounds that are useful for the production of various pharmaceuticals. 

Bromide ions are effective in reducing the sensitivity of the central nervous system. This is why they find application in the manufacture of anticonvulsants, sedatives, and tranquilizers. They are also present in several over-the-counter and prescription drugs.

Petrochemical industries

Bromide ions are actively involved in processes, such as alkylation and polymerization in the petrochemical industry. Their charge influences their catalytic activity in complex hydrocarbon systems.

In the control of mercury emission

Bromide ions are anions. They enhance the capturing of mercury vapor in coal-fired power plants. They form stable compounds via which toxic mercury is removed from the atmosphere.


Is the charge of bromine the same as its valency?

Yes, the charge of bromine is the same as its valency. Valency refers to the combining power of an element. It can also be determined by the number of electrons in its outermost shell.

However, for elements like halogens, the valency is determined by the number of valence electrons they gain in chemical reactions.

Can bromine form cations?

Bromine forms anions instead of cations. It has seven electrons in its outermost shell and gains one more to complete its octet. The extra electron it gains makes it have more electrons than protons.

Does the charge of bromine change in chemical reactions?

Yes, it is. The charge of bromine changes depending on how it reacts with other elements. Atoms gain or lose electrons to form anions or cations, respectively. However, bromine is more likely to form anions because it gains one electron to complete its octet and attain stability.


All members of the halogen family have seven electrons in their outermost shell. To attain stability and complete octet, they gain one electron. This is the same way bromine reacts to achieve a -1 charge.

The negative charge of bromine and all other halides influences their participation in the formation of metal bromides and other halides.

The bromide ion is not only important to scientific reactions, but it also makes it useful in water treatment, the production of flame retardants, and in pharmaceutical and petrochemical industries.

Chlorine is the preceding halogen to bromine. You can also learn about the charge of chlorine and its various applications.

Thanks for reading.