P-Block Elements and Their Compounds-II: Group 17 Elements (For CBSE, ICSE, IAS, NET, NRA 2022)

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Group 17 Elements

  • All members of Group 17 are non-metallic.
  • Fluorine and chlorine are gases, bromine is a volatile liquid, and iodine is a dark shiny colored solid. Astatine is radioactive and very short-lived.
  • These elements can enter into chemical combination and complete their octets by gaining one electron to form the 1-valent ion, e. g. , , etc. and by forming one covalent bond, e. g. the elements themselves , , , and their hydrides , , and .

Physical Properties of Group 17 Elements

Physical Properties of Group 17 Elements


  • Fluorine and chlorine are fairly abundant, bromine and iodine less
  • Fluorine is present mainly in the insoluble fluorides of calcium: calcium fluoride; cryolite, , and fluorapatite, .
  • Sea-water contains the chlorides, bromides, and iodides, of sodium, potassium, magnesium, and calcium.
  • Some marine life concentrate iodine in their systems.


  • Fluorine is extremely difficult to prepare owing to its highly reactive nature.
  • It is the strongest chemical oxidizing agent hence cannot be prepared by oxidation of fluoride ions.
  • It is prepared by the electrolysis of potassium hydrogen fluoride in anhydrous hydrogen fluoride.

  • Fluorine is a pale-yellow gas which fumes in air.
  • Fluorine is highly reactive. It combines with various metals and non-metals to form fluorides.
  • With hydrogen halides it acts as an oxidizing agent, e. g.


Chlorine is prepared by the oxidation of chlorides by strong oxidizing agents, such as .

  • On a large scale it is obtained as a by-product in the electrolysis of sodium chloride.
  • Chlorine is a greenish yellow gas and can be liquified by pressure alone at room temperature.
  • It is quite reactive and forms chlorides of metals and non-metals.
  • It also oxidizes ammonia to nitrogen.

Large quantities of chlorine are used in bleaching industry.

Hydrogen Halides and Hydrohalic

  • The bond distance H – X increases with the size of halogen atom.
  • The acid strength increases in the order because the hydrogen halide in aqueous solution loses hydrogen ion more easily with increasing size of halogen.
  • The aqueous solutions of hydrogen halides are known as hydrohalic acids or simply halogen acids.

Preparation of Halogen Halides

is made by heating with strong .

Hydrogen chloride is made by heating a mixture of and conc. at .

Phosphoric acid is used to make

We use red phosphorus for making and .

Properties of Halogen Halides

  • HF is a liquid at room temperature , whereas and are gases.
  • The boiling point of HF is unexpectedly high as compared to , and .
  • This is due to the formation of hydrogen bonds between the F atom of one molecule and the H atom of another molecule (Fig) .
Properties of Halogen Halides

The bond dissociation energy of the hydrogen halides follow the order .

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