Group 17 Elements (Halogen Family): Configuration, Properties and Uses

Imagine a world without disinfectants, bleaches or even common table salt. These familiar substances are but a few examples of the many products whose fabrication is made possible by the intriguing elements of Group 17, the Halogen family of nonmetals. The name "halogen" means "salt-former," which reflects that many of these elements react with metals to form salts. The elements belonging to group 17 reach into important applications at various ends, from water purification to medical treatments. Owing to their ability to exhibit high reactivity, the halogens can combine with almost all other elements to form compounds.

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This Story also Contains

1. Physical Properties of Group 17 - 1
2. Physical Properties of Group 17 - 2Various Aspects of Halogen Elements
3. Relevance and Applications
4. Summary

That makes them a necessity, quite absolutely speaking, in a number of chemical reactions and industry processes. For instance, huge amounts of chlorine are used in treating water to kill pathogenic microorganisms and ensure safe drinking water. Fluorine compounds, as in toothpaste, prevent tooth decay by strengthening enamel. It's bromine that makes things less combustible by its introduction into flame retardants. Iodine is also crucial for thyroid health, preventing things like goiter. At the very least, astatine was so rare and so little understood that research with its radioactive properties was done at least for use in treatment against certain cancers. We shall relate the physical properties of these elements and their relevance to real-life/academic applications.

We shall start with some basic concepts and definitions forming the foundation necessary for understanding unique characteristics in the general nature of halogens. This shall be followed by explanations of different features of the elements in relation to their physical states and reactivity. I will be learning about different practical applications and why they are important in many ways. By the end of this paper, you will be given an overall understanding of the capacity of group 17 elements and their essential place in our world.

Physical Properties of Group 17 - 1

Concept and General Definitions

Group 17 elements are also called halogens, which means a group of highly reacting elements capable of forming salts.

The second to the last column consists of fluorine, chlorine, bromine, iodine, and astatine. Each of these elements possesses seven valence electrons. Being highly reactive, each one of them wants to gain one more electron to attain its stable octet configuration. So, high reactivity can be confidently said to be one of the characteristic features of this halogen group, which defines their physical and chemical properties.

Physical Properties of Group 17 - 2
Various Aspects of Halogen Elements

Physical features of halogen elements lie at opposite extremes.

For instance, fluorine exists in the form of a pale yellow gas, chlorine in greenish-yellow gas, bromine—in reddish-brown liquid, iodine in gray or purple, and astatine, which is a metal that is radioactive and little known, is rarely seen in solid form. Section Summary The reason that fluorine and chlorine are gases at room temperature, bromine is a liquid and iodine is a solid is that the melting and boiling points of these elements increase down a group. These variations are attributed to the increased strength of intermolecular forces as the size of atoms increases down the group.

The trends of some of the atomic, physical, and chemical properties are discussed below.

Electronic Configuration
All these elements have seven electrons in their outermost shell (ns²np⁵) which is one electron short of the next noble gas.

Atomic and Ionic Radii
The halogens have the smallest atomic radii in their respective periods due to the maximum effective nuclear charge. The atomic radius of fluorine like the other elements of the second period is extremely small. Atomic and ionic radii increase from fluorine to iodine due to the increasing number of quantum shells.

Ionisation Enthalpy
They have little tendency to lose electrons. Thus they have very high ionisation enthalpy. Due to an increase in atomic size, ionization enthalpy decreases down the group.

Electron Gain Enthalpy
Halogens have maximum negative electron gain enthalpy in the corresponding periods. This is due to the fact that the atoms of these elements have only one electron less than stable noble gas configurations. Electron gain enthalpy of the elements of the group becomes less negative down the group. However, the negative electron gain enthalpy of fluorine is less than that of chlorine. This is due to the small size of the fluorine atom. As a result, there are strong interelectronic repulsions in the relatively small 2p orbitals of fluorine and thus, the incoming electron does not experience much attraction.

Electronegativity
They have very high electronegativity. The electronegativity decreases down the group. Fluorine is the most electronegative element in the periodic table.

Oxidation states
All the halogens exhibit a –1 oxidation state. However, chlorine, bromine and iodine exhibit +1, +3, +5 and +7 oxidation states also. The higher oxidation states of chlorine, bromine, and iodine are realized mainly when the halogens are in combination with the small and highly electronegative fluorine and oxygen atoms, e.g., in interhalogens, oxides, and oxoacids. The oxidation states of +4 and +6 occur in the oxides and oxoacids of chlorine and bromine. The fluorine atom has no d orbitals in its valence shell and therefore cannot expand its octet. Being the most electronegative, it exhibits only –1 oxidation state.

Relevance and Applications

There exist a few important applications for halogens, both in everyday life and in many scientific respects. Chlorine is used in water supplies, killing off all the bacteria and thereby providing safe water. Again, it happens to form an important ingredient in most cleaning powders. For example, fluorine compounds are added to toothpaste and even to the water supply in some places, particularly sodium fluoride, to prevent dental cavities. Iodine allows for thyroid health; lack of it causes goiter, which is an enlarged thyroid. Some uses for bromine are found in flame retardants, and its compounds make materials less flammable. Astatine is not found so abundantly, but it has radioactive properties that have made it useful in research against cancer. Besides, there is also an important place for halogens in academic research because of this unusual reactivity and the ability to form compounds with almost all elements. This makes them very interesting in inorganic chemistry, especially in organic synthesis, where they are mostly used as an intermediate or a reagent.

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Some Solved Examples

1. When a mixture of FeSO₄ and KNO₃ reacts with H₂SO₄, what gas is produced?

1. NO
2. SO₂
3. NO₂
4. SO₃

Solution:
The reaction of FeSO₄ and KNO₃ with H₂SO₄ can be represented by the following chemical equation:
$[ 2KNO_3 + 5H_2SO_4 + 6FeSO_4 \rightarrow 2KHSO_4 + 3Fe_2(SO_4)_3 + 4H_2O + 2NO ]$

From the equation, it is clear that nitric oxide (NO) is produced.

Hence, the correct answer is option (1) NO.

2. What is the correct order of bond dissociation enthalpy of halogens?

1. $( \mathrm{Cl_2 > F_2 > Br_2 > I_2} )$
2. $( \mathrm{I_2 > Br_2 > Cl_2 > F_2} )$
3. $( \mathrm{Cl_2 > Br_2 > F_2 > I_2} )$
4. $( \mathrm{F_2 > Cl_2 > Br_2 > I_2} )$

Solution:
The bond dissociation enthalpy is influenced by the size and the repulsions between non-bonding electrons (lone pair-lone pair repulsions). For halogens, the bond dissociation enthalpy order is influenced by these factors. Due to its small size, $(\mathrm{F_2})$ involves repulsions of non-bonding electrons, making its bond dissociation energy lower than that of $(\mathrm{Cl_2})$ and $(\mathrm{Br_2})$, but not less than $(\mathrm{I_2})$.

So, the correct order of bond dissociation enthalpy of halogens is:
$[ \mathrm{Cl_2 > Br_2 > F_2 > I_2} ]$

Hence, the correct answer is option (3).

3. The electron gain enthalpies of halogens in kJmol are given as:
$[ \mathrm{F = -332, Cl = -349, Br = -324, I = -295} ]$
The less negative value for $(\mathrm{F})$ as compared to $(\mathrm{Cl})$ is due to:

1. Strong electron-electron repulsions in the compact $(\mathrm{2p})$ subshell of $(\mathrm{F})$
2. Weak electron-electron repulsions in the compact $(\mathrm{2p})$ subshell of $(\mathrm{Cl})$
3. Smaller electronegativity value of $(\mathrm{F})$ than $(\mathrm{Cl})$
4. (A) and (B) both

Solution:
Due to the small size of the $(\mathrm{F})$ atom, the electron-electron repulsions in the compact $(\mathrm{2p})$ subshell are greater. Hence, the incoming electron is not accepted with the same ease as in the case of $(\mathrm{Cl})$ because of lesser electron-electron repulsions in $(\mathrm{Cl})$.

Hence, the correct answer is an option (4)

Summary

Thus, the halogen group 17 is an extremely interesting group to deal with highly reactive elements, covering an enormous range of physical properties.

From pale yellow gas fluorine to dark solid iodine, these elements play a big role in many industrial, medicinal, and everyday applications. Highly reactive, having a route to form salts, makes them of immense importance. Their properties and applications would help in understanding their day-to-day and academic importance.