The P-Block Elements: Group 17 Elements

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The elements of the group 13 – 18 come under the p – block elements. In these elements the last electron enters in the outermost p – orbital. They have ns2np1-6 electronic configuration in valence shell, helium being an exception. These elements show the maximum oxidation state equal to the sum of electrons in the outermost shell or valence shell. Most of the elements of the p – block form covalent compounds although some elements form ionic compounds (such as halogens) and coordination compounds as well. p-block contains elements which are either metals, non – metals or metalloids. p-block elements include the group of halogens and inert gases. First member of each family of the p-block elements is given below in the table with their general electronic configuration and oxidation states. p-block has the most electronegative element which is fluorine. Elements of p-block generally form acidic oxides. Many elements such as C, Si, Ge, O, N etc. also show phenomenon of allotropy. Property of catenation is also shown by many elements.  








First Member of the Group


General Electronic Configuration 







Group Oxidation State 







We have covered the Boron Family (Group -13 elements), the Carbon Family (Group – 14 elements), the Nitrogen Family (Group – 15 elements) and the Oxygen Family (Group – 16 elements) in other articles based on p-block elements. In this article, we will cover the Halogen Family or Group 17 Elements of p-block elements (Class XII, Chemistry). 

Group 17 Elements: The Halogen Family 

Group 17 is the fifth group of p-block elements. The word Halogens is made up of two Greek words Halo and genes. Halo means salt and genes means born, thus halogen means salt producers. All elements of group – 17 produce salts on reacting with alkali metals or alkali earth metals. That’s why this group is also known as the Halogen family and this group elements are called halogens. 

Elements of the Group - 17

Atomic number 



Color & State 

Electronic Configuration 

Density g/cm3 at 298 K

Atomic and Ionic Radii 

Ionization Enthalpy 




Pale yellow colored 


[He] 2s2 2p5


Increases on moving from top to bottom in the group due to increase in the number of shells. 

Decreases on moving from top to bottom in the group due to gradual increase in size of elements.




Pale yellow – green colored


[Ne] 3s2 3p7





Reddish – brown 


[Ar] 3d10 4s2 4p5





Metallic gray (Lustrous)


[Kr] 4d10 5s2 5p5



At (Radioactive element)


[Xe] 4f14 5d10 6s2 6p5



Ts (Synthetic Chemical element)



[Rn] 5f14 6d10 7s2 7p5

Elements of the Group 17 – Physical Properties 


Atomic Number 

Atomic Mass (g mol-1)

Melting Point (K)

Boiling Point (K)


Ionic Radius 






Increases on moving from top to bottom in the group


Increases on moving from top to bottom in the group

Increases on moving from top to bottom in the group 

Increases on moving from top to bottom in the group.

Decreases on moving from top to bottom in the group. 

Fluorine is the most electronegative element.
















At (Radioactive element)





  • Electron gain enthalpy of the elements of the group -17 becomes less negative on moving down the group.

  • Halogens have maximum negative electron gain enthalpy in the corresponding periods.

Elements of the Group 17 – Chemical Properties

Oxidation Number 

Group -17 elements generally exhibit only -1 oxidation state.

Other than -1 oxidation state Cl, Br, I exhibit +1, +3, +5 and +7 oxidation state. 

The oxidation states of +4 and +6 occur in the oxides and the oxoacid of chlorine and bromine. 

Reactivity Towards Oxygen  

All elements of the halogen family form oxides but most of these oxides are unstable in nature. 

Fluorine forms two oxides OF2 and O2F2.

As we move down the group, the stability of halogen oxides decreases. 

Reactivity with Hydrogen 

All elements of the halogen family react with hydrogen and form hydrogen halides. Although as we move down the group stability of these halides decreases. 

As we move down the group, affinity for hydrogen decreases. H-X bond dissociation enthalpy order of halogens –

H–F > H–Cl > H–Br > H–I

Acidic character of the hydrides of group 17 elements increases on moving down the group as the bond enthalpy of H-E bond decreases on moving down the group. 

HF < HCl < HBr < HI

Reaction Towards Metal 

All elements of the halogen family react with metals and form metal halides. 

The ionic nature of metal halides decreases as we move down the group. 

MF > MCl > MBr > MI

M = any monovalent metal 

The halides in higher oxidation state will be more covalent than the one in lower oxidation state. Such as SnCl4 is more covalent in nature than SnCl2

Anomalous Properties of Fluorine 

  • Fluorine differs from other elements of the group – 17 due to its high electronegative character, small size, low F-F bond dissociation enthalpy and high ionization enthalpy. 

  • Fluorine mostly shows exothermic reactions. 

  • It forms only one oxoacid while other elements of the group – 17 form many oxoacids. 

  • Hydrogen fluoride is liquid while other hydrogen halides are gases. fluorine forms a very strong bond with hydrogen due to its small size and high electronegative nature. 

  • d- orbitals are not found in the valence shell of the fluorine atom. 


Chlorine – Group – 17 element: Preparation, Properties and Uses





Cl was discovered by Scheele in 1774. It was named by Davy in 1810. 

The name comes from the Greek word chloros which means greenish yellow. 

🡪 By heating manganese oxide with HCl. 

Reaction –

MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O

🡪 By the reaction of hydrogen chloride and potassium permanganate. 

Reaction –

2KMnO4 + 16HCl → 2KCl + 2MnCl2 + 8H2O + 5Cl2

🡪Deacon’s process – In this process, oxidation of HCl is done by atmospheric O2 in presence of catalyst cupric chloride at 723 K temperature. 

Reaction –

4HCl + O2 CuCl2 2Cl2 + 2H2

🡪 Electrolytic process – Chlorine can be obtained by the electrolysis of brine solution or conc. NaCl solution. 

🡪 Pale yellow green colored gas which has a pungent smell. 

🡪 It has a suffocating odor. 

🡪 It is heavier than air. 

🡪 It easily reacts with various metals and forms metal chloride. 

2Al + 3Cl2 → 2AlCl3

2Fe + 3Cl2 → 2FeCl3

🡪 It is soluble in water. 

🡪 It reacts with hydrogen and compounds containing hydrogen. For example –

H2 + Cl2 🡪 2HCl 

🡪 It produces a mixture of chloride and hypochlorite with cold and dilute alkalies.

2NaOH + Cl2 → NaCl + NaOCl + H2O

🡪 It reacts with hydrocarbons. With saturated hydrocarbons, it gives substitution products while with unsaturated hydrocarbons, it gives addition products. 

🡪 It is used for bleaching textiles, cotton cloths and wood pulp.  

🡪 In many disinfectants, pesticides etc.

🡪 It is used in the manufacture of various drugs and organic compounds. 

🡪 It is used in sterilizing drinking water.

It bleaches vegetables and other organic matter in presence of moisture. 

Cl2 + H2O → 2HCl + O 

Colored substance + O → Colorless substance

🡪 It is used in preparation of phosgene, tear gas and mustard gas.  

Hydrogen Chloride 

Chlorine – Group – 17 element: Preparation, Properties and Uses





It was discovered by Glauber in 1648. Then in 1810, Davy showed that it is a compound of chlorine and hydrogen. 

🡪 Laboratory method – It is prepared by heating NaCl with conc. sulphuric acid at 420 K temperature. 

NaCl + H2SO4 🡪 NaHSO4 + HCl (420 K)

NaHSO4 further reacts with sodium chloride and forms Na2SO4 and HCl.

NaHSO4 + NaCl 🡪  Na2SO4 + HCl

🡪 It is a gaseous compound which has a pungent smell. 

🡪 Its boiling point is 189 K.

🡪 Its freezing point is 159 K. 

🡪 In liquid state, it is colorless. 

🡪 It is highly soluble in water.

HCl + H2O 🡪 H3O+ + Cl- 

🡪 It is a strong acid. 

🡪 Its mixture with conc. nitric acid is called aqua regia. In aqua regia, one part of conc. HNO3 and three parts of conc. HCl are mixed. 

🡪 It reacts with ammonia and gives white fumes of ammonium chloride. 

Reaction – 

NH3 + HCl → NH4Cl

🡪 Its mixture aqua regia is used for dissolving many metals. 

🡪 It is used in the manufacture of chlorine, glucose and ammonium chloride. 

🡪 It is used as a laboratory reagent.

🡪 It is used in manufacturing medicines. 

Oxoacids of Halogens 

An oxoacid is an acid that contains oxygen. Oxoacids of halogens contain oxygen, hydrogen and halogen atoms. For examples, HOF, HOCl, HOBr, HOI etc. 

Fluorine forms only one oxoacid which is HOF due to its high electronegativity and small size. 

Most of the oxoacids of halogens are not stable. They are stable either in aqueous solution or in the form of their salts. Structure of few oxoacids of chlorine are given below –

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Interhalogen Compounds 

Interhalogens compounds are those compounds which are formed by the reaction of two different halogens. They can be assigned general compositions as XX′ , XX3′, XX5′ and XX7′ where X is larger size halogen and X′ of smaller size and X is more electropositive than X′. As the ratio between radii of X and X′ increases, the number of atoms per molecule also increases.

Interhalogen compound: Preparation, Properties and Uses




By direct reaction of two different halogens

Reaction – 

Cl2 + F2 🡪 2ClF (At 437 K) 

🡪 ClF is a colorless gas. 

🡪 BrF is pale brown gas.

🡪 ClF3 is a colorless gas. 

🡪 ClF5 is a colorless liquid.

🡪 BrF5 is also a colorless liquid. 

🡪 They are all covalent and diamagnetic in nature.

🡪 these compounds are used as solvents mostly non aqueous solvents. 

🡪 Interhalogen compound of fluorine are very useful fluorinating agents. For example, used for the production of UF6

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