Characteristics of Halogens

Halogens, in the periodic table, correspond to the elements of group 17 or family VII A.

What are halogens?

Halogens are made up of 6 elements:

  • Fluorine
  • Chlorine
  • Bromine
  • Iodine
  • Astatine
  • Ununseptium

Characteristics of halogens

Halogens are strong oxidants and react mainly with alkali metals (family IA) that have the tendency to give up an electron.

They also react with metals and noble gases (family VIII A). Along with the noble gases , halogens are made up of non-metals. All elements in this group form diatomic molecules, for example F 2 , Cl 2 , Br 2 , I 2 .

They have a common characteristic which is to present 7 electrons in the last valence shell based on the electronic configuration (np 5 ).

Therefore, they have the tendency to gain an electron. Through ionic bonding, they result in a monatomic anion, monovalent negative ions (X -1 ) called halide ions. Sodium chloride (kitchen salt) Na + Cl is an example.

Properties of halogens

The 7th family is made up of six elements that, except for iodine, are all toxic.

Fluorine (F)

Fluorine is considered the most electronegative and reactive element in the Periodic Table. It is the most abundant halogen in the Earth’s crust, with a pungent odor, atomic number 9, that is, 9 protons and 9 electrons, and atomic mass 19.

It is a corrosive gas, highly dangerous and toxic, and can cause serious burns in contact with the skin.

In small doses, fluoride strengthens bones, and is widely used in the pharmaceutical industry as tranquilizers, in dental treatments and in water treatments (water fluoridation).

Chlorine (Cl)

Chlorine, like fluorine, occurs in nature in gaseous form.

Its atomic number is 17, that is, 17 protons and 17 electrons. Its atomic mass is 35.45.

It has the ability to kill harmful microorganisms (bacteria, fungi) found in water, presenting a disinfectant action.

In this way, they are used in water and sewage treatment, in cleaning swimming pools and in industrial activities (paper manufacturing).

Additionally, it is used in food. For example, sodium chloride (NaCl), popularly known as table salt.

The lack of this compound in the body can cause problems in the thyroid gland. The chloride ion (Cl ) is a necessary component for the formation of hydrochloric acid (HCl), an essential component of our gastric juice.

Bromine (Br)

Bromine, a volatile, unstable, highly reactive and reddish element. It has atomic number 35 (35 protons and 35 electrons) and atomic mass equal to 80.

This element, in aqueous presence, is considered a strong oxidant. It is found in a liquid state and its toxicity can cause allergic reactions in the eyes, tissues and throat.

It is widely used in industry, in agriculture, in the manufacture of medicines, dyes, disinfectants, insecticides. It is also used in some organic reactions, photographic developments, gasoline additives, among others.

Iodine (I)

Iodine is a halogen with atomic number 53, that is, it has 53 protons and 53 electrons and an atomic mass of 126.9.

Among the elements that make up family VII A, iodine is the one with the lowest reactivity and electronegativity.

They are found at room temperature, in their solid form (black, shiny solid). It has bactericidal action, being widely used in the food and disinfectant industries, nuclear medicine, photography (potassium iodide), among others.

In addition to that, the lack of this element in humans can cause a disease called goiter. For this reason, iodine is added to sodium chloride (iodized table salt).

Astatine (At)

Astatine is an element found in small quantities in nature and highly radioactive. It has atomic number 85 (85 protons and 85 electrons) and atomic mass 210.

At room temperature they are found in solid form. Among the halogens, astatine is considered the heaviest and most oxidizing element, which has five oxidation states.

This element is used in the development of scientific research and little is still known about its effects.

Applications in everyday life

Fluoride can be found in the toothpaste we use and is extremely corrosive to glass and should always be stored in another type of container.

Chlorine is used in swimming pool water treatment and is also present in the table salt that we use daily.

In addition to that, it is also part of the composition of products that have whitening power, such as products that remove stains from clothing.

Chlorine and fluorine are also contributors to the increase in the greenhouse effect in the form of chlorofluorocarbons (CFCs), formerly used in aerosols.

Bromine is found in products intended for the extermination of insects in the form of bromide . Iodine is part of the composition of table salt.

This is the only halogen group that is non-toxic and, together with chlorine, has antibacterial action.

Astatine still has no applications, being only the object of theoretical study as well as unuseptium.


The word halogen comes from Greek and means “ salt former .”

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