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Group 17 Elements – General Trends, Properties, Position of Halogens in the Periodic Table, Practice Problems and FAQ

Meena, a 10-year-old girl, and her pals were playing Kho-Kho in the schoolyard. Meena tripped and fell to the ground while attempting to catch one of her friends. She was bleeding and had cut wounds on her knees and elbows. Her pals escorted her to the PE instructor (P.E.T.) so she could complain about the situation. Meena was told by her teacher to remain calm. The instructor cleaned the cuts with water before applying a dark-brown solution. The bleeding ceased after being treated with the dark solution.

Do you recognise the dark-brown liquid?

Iodine tincture solution is what it is.


One of the elements of group 17, iodine, has numerous crucial uses. There are several uses for other Group 17 elements like fluorine, chlorine, and bromine. Fluorine is a key ingredient in toothpaste, whereas chlorine aids in the purification of water in swimming pools.

We will go through the main characteristics of group 17 elements in more detail and discover how the periodic table's trends change on this concept page.


  • Group 17 Elements – Introduction
  • Group 17 Elements – Electronic Configuration
  • Group 17 Elements – Properties
  • Group 17 Elements – General Trends
  • Practice Problems
  • Frequently Asked Questions – FAQ

Group 17 Elements – Introduction

VII-A, a group of elements from the periodic table's p-block, includes the elements that make up Group 17 components. These highly reactive non-metal elements, including fluorine, chlorine, bromine, iodine, astatine, and tennessine, make up this group. These elements were given the term "halogen," which in Greek means "to produce salt," since they may interact with the element sodium to form salts.

These elements are grouped together as they are all extraordinarily reactive and have many chemical characteristics in common. However, some patterns may be seen in the group, distinguishing the elements. While the other elements in this category typically exist in mixed form, astatine and tennessine are radioactive elements that have been specially created.


Group 17 Elements – Electronic Configuration

The valence shell electronic configuration of all the group 17 elements is the same. The general representation is ns2 np5, where ‘n’ is the shell number.


Atomic number

Electronic configuration



He 2s2 2p5



Ne3s2 3p5



Ar4s2 3d10 4p5



Kr5s2 4d10 5p5



Xe6s2 4f14 5d10 6p5



Rn7s2 5f14 6d10 7p5

The outermost shell of halogen elements has 7 electrons, as may be shown from the electronic configurations of group 17 elements. It simply takes one more electron to stabilise their valence p-orbital. Halogens are extremely electronegative and reactive due to the high valency of their electrons. The last electron in group 17 elements enters the p-orbital, and is therefore placed in the p-block of the periodic table.

Group 17 Elements – Properties

Physical state

At room temperature, halogens can be found in different states of matter. As covalent diatomic molecules, halogens are kept together by a weak van der Waals force of attraction, but as the molecular mass grows, so does this force, changing the physical state of halogens as one moves down the group. Iodine, astatine, and tennessine are solids, whereas fluorine and chlorine are gases, and bromine is a liquid.


Due to their non-polar nature, halogens are typically insoluble in water. However, fluorine interacts with the water molecule to produce oxygen and ozone.

2F2g+ 2 H2Ol4HFaq+ O2g

3F2g+ 3 H2Ol6HFaq+ O3g

Due to their non-polar character, elements in this group such (Cl2, Br2, I2 are more soluble in organic solvents like carbon tetrachloride (CCl4), chloroform (CHCl3), etc.


Each element in this group has a different colour. The amount of energy released as an electron returns from a higher energy state to a lower energy level results in an electromagnetic wave that is visible to the human eye, which determines the colour of the elements. The colours of the elements of the halogen group are listed below (in the diatomic state).










Deep violet



Oxidation State:

Since all members of the halogen group have seven valence electrons and only require one additional electron to complete their respective shells when combining with the less electronegative element, all members of the halogen group generally exhibit the ( -1) oxidation state.

Since fluorine is the most electronegative element in the periodic table, and is in the second period, it does not have any free d-orbitals where valence electrons might be excited to exhibit numerous oxidation states. As a result, fluorine consistently exhibits the ( -1) oxidation state.

On the other hand, due to the availability of unoccupied d-orbitals in the valence shell, chlorine, bromine, and iodine can create compounds with higher oxidation states as well, such as +1, +3, +5, and +7.

An element's oxidation state also affects how well it may interact with other elements. In order to make salts, elements with an oxidation state of ( -1) can accept an electron from other elements.

From fluorine to astatine, the Group 17 elements' oxidation strengths weaken. Thus, fluorides, the compounds formed by fluorine, are the most stable.

Oxidation state






HF, NaF, MgF2,

XeF4 etc.

NaCl, MgCl2, HCl

CaCl2 etc


AgBr etc.

NaI,HI, MgI2 etc.


No compound

HClO, Cl2O etc

HBrO, Br2O etc

ICl, HIO etc


No compound

ClF3 , HClO2




No compound





No compound


BrF5, HBrO3



No compound


Br3O8(2 bromine atoms are in +6 oxidation state and one bromine atom is in +4 oxidation state)

No compound


No compound


No compound


Group 17 Elements – General Trends

Atomic and Ionic Radii

  • Atomic radii refer to the distance in an atom between the nucleus's centre and its outermost electron.
  • Ionic radii refer to the separation between the nucleus's centre and its outermost electron in an ion.
  • Since halogens are members of group 17 and have seven electrons in their outermost orbital, they have the shortest radii among the other elements in their respective periods. This is due to the fact that as we move from left to right in a period, the number of electrons increases by one unit. As a result, the size of the atom is decreased by the attraction of electrons towards the nucleus.
  • The number of shells increases as we move down the group in group 17 (from fluorine to iodine), and as we move down the group, both atomic and ionic size also increases.

Order of atomic size in group 17: F<Cl<Br<I

Order of ionic size (X-): F-<Cl-<Br-<I-

Ionisation Enthalpy

  • The amount of energy needed to remove the outermost valence electron from a ground state isolated gaseous atom is known as the Ionisation enthalpy.
  • Ionisation enthalpy is greatest for fluorine. From fluorine to iodine, the ionisation enthalpy value falls because as the number of shells grows, the attraction force between the valence electrons and the nucleus weakens, making it simpler to remove an electron from an atom's valence or outermost shell.

Order of ionisation enthalpy in the group 17: F>Cl>Br>I

Electron Gain Enthalpy

  • The amount of energy released when an electron is added to the valence shell of a ground-state isolated gaseous atom is known as the Electron gain enthalpy.
  • As we descend the group from fluorine to iodine, the electron gain enthalpy value decreases. Because of its tiny structure and higher electron density than chlorine, fluorine repels incoming electrons, causing their energy to drop. This is why fluorine has a far lower electron affinity than chlorine.

Order of electron gain enthalpy in the group 17: Cl>F>Br>I

Note: The electron gain enthalpy value for group 17 elements is negative, indicating that energy is released when the electron is added to the valence shell of an isolated gaseous atom.


  • Electronegativity is the tendency of an atom in a covalently bound molecule to draw the shared pair of electrons further toward itself.
  • The elements of Group 17 are extremely electronegative in their respective rows, and down the group, as new shells are added, the group's electronegativity value drops.

Order of electronegativity in the group 17: F>Cl>Br>I

  • Among the halogen atoms, fluorine has the highest electronegativity.
  • The non-metallic nature of an element changes from fluorine to iodine as a result of a fall in electronegativity value.

Atomic Volume and Density

  • Iodine has a higher atomic volume and density than fluorine has in its liquid state.
  • I>Br>Cl>F is the trend of group 17's atomic volume.
  • I>Br>Cl>F is the trend of group 17's density in a liquid state.

Bond Dissociation Energy

  • When atomic size increases, the bond dissociation energy decreases. As atomic size increases down the group, fluorine is expected to have a higher bond dissociation energy than other halogens with iodine having the least bond dissociation energy.
  • But due to significant electron repulsion among non-bonding electrons in the 2p- orbitals of the fluorine atom, the bond dissociation energy of F2 is lower than that of Cl2 and Br2.
  • The group 17's bond dissociation energy is in the following order: Cl2>Br2>F2>I2

Reduction Potential and Oxidising Nature

  • Halogens have positive standard reduction potential values that decrease from fluorine to iodine. The easier the element can be reduced, the higher is the positive value of reduction potential.
  • The order of standard reduction potential values for the group 17 elements is F2>Cl2>Br2>I2.

Reduction Half Reaction

Standard Reduction Potentials, E°(Volt)


2.87 V


1.36 V


1.09 V


0.54 V

  • The oxidising power of halogens decreases from fluorine to iodine. Halogens have a strong oxidising effect.
  • This trend is observed in the group-17 elements as they are the most electronegative element in their respective period, but it decreases down the group because the electronegativity decreases on moving down the group and as a result the oxidising power also decreases.
  • The order in oxidising power value for the group 17 can be ordered as F2>Cl2>Br2>I2
  • For example, fluorine when combined with water, oxidises the oxygen present to form oxygen or ozone.

2F2g+ 2 H2Ol4HFaq+ O2g

3F2g+ 2 H2Ol6HFaq+ O3g

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Practice Problems

Q1. Which of the following is the most reactive element?

A. I
B. Cl
C. F
D. Br

Answer: C
Solution: Fluorine is the most reactive halogen, which is why it is also known as a super halogen. It is the most electronegative element in the periodic table with a value of 4.0 on the Pauling scale. This suggests that fluorine has a strong tendency to attract electrons and be reactive.

So, option C is the correct answer.

Q2. What is the general electronic configuration of halogens?

A. ns2np3
B. ns2np2
C. ns2np4
D. ns2np5

Answer: D
Solution: Since the valence shell of the elements in group 17 has seven electrons, their general electrical configuration is ns2np5, or ns2npx2npy2npz1,, where n=2 to 6 . As a result, they have one less electron than the nearby inert gas configuration.

So, option D is the correct answer.

Q3. Which of the following is the correct order of dissociation enthalpies of halogens?

A. I2>Br2>Cl2>F2
B. Cl2>Br2>F2>I2
C. Cl2>F2>Br2>I2
D. F2>Cl2>Br2>I2

Answer: B

Solution: Due to an increase in atom size as we go down the halogen group from F to I , the enthalpy of dissociation reduces as the bond distance increases from F2 to I2 .

However, the enthalpy of the F-F bond dissociation is lower than that of the Cl-Cl bond and even lower than that of the Br-Br bond. This is because the electron-electron repulsions between the lone pairs of electrons in fluorine are extremely strong due to the small size of the F atom. The bond between the two fluorine atoms is weakened by the strong electron-electron interactions between their lone pairs of electrons.

Therefore, the correct order of dissociation enthalpies of halogens is Cl2>Br2>F2>I2.

So, option B is the correct answer.

Q4. What is the atomicity of the halogen molecules?

A. One
B. Two
C. Three
D. Four

Answer: B
Solution: In comparison to the closest inert gas, each halogen has one electron less. Halogens are hence extremely reactive elements. They easily establish covalent connections with other atoms by sharing their lone unpaired electron. As a result, all halogens are diatomic molecules.

So, option B is the correct answer.

Frequently Asked Questions – FAQ

Q1. Who discovered chlorine?
Answer: Carl Wilhelm Scheele heated HCl and MnO2 to create chloride in 1774. On the basis of its colour, Davy proposed the term chlorine (Greek: chloros = greenish-yellow) in 1810 and confirmed its elemental nature.

Q2. The halogens produce what kind of bonds?
Answer: Ionic and covalent bonds are formed by halogens. Halogens bond with non-metals through covalent bonds. Atoms share electrons in covalent bonds. Atoms that share comparable electronegativity form covalent bonds. For instance, halogens can combine with hydrogen to form covalent bonds that result in acids like hydrofluoric acid (HF) and hydrochloric acid (HCl).

The alkali metals in group 1 of the periodic table are particularly good candidates for forming ionic bonds with halogens. Since the two atoms in an ionic bond have significantly different electronegativities, one atom gives an electron to the other. For instance, sodium readily gives one to chloride to create sodium chloride or table salt. In this bond, chlorine has a negative charge and sodium has a positive charge; both have a complete outer shell.

Q3. What happens if a halogen is subjected to sunlight?
Answer: Hydrogen chloride gas is created when a chlorine and hydrogen mixture is exposed to light or a flame and explodes. Lighting a hydrogen jet and dropping it into a gas jar of chlorine can control this process. The formation of hydrogen chloride gas continues to occur as the hydrogen burns more slowly and uniformly.

Q4. HF is the only liquid among the other hydrides of halogen at room temperature. Why?
Answer: HF is the only liquid among the other hydrides of halogen at room temperature. The hydrogen bonds that form between the F atom of one molecule and the H atom of another molecule are what cause HF to have an unexpectedly high boiling point. This is the main reason of HF to exist liquid at room temperature.

Related Topics


Group-14 elements

Chemical properties of group-13


Bleaching powder

P-block elements

Interhalogen compounds

Oxoacids of halogen

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