Class 12 Chemistry P Block Elements Chemical properties of group 16

Chemical properties of group 16

Trends in chemical reactions:

  • The order of reactivity of group 16 elements is:


  That is oxygen is quite reactive and as we move down   reactivity decreases.

  • Oxygen in this group is quite reactive as the bond between oxygen atoms is quite strong and the energy required to break it is 493.3kJ/mol.
  • Almost all the reactions of oxygen are exothermic, therefore, the reactions are called combustion reaction.


The most stable compounds of this group are: selenides and tellurides.


  1. Reaction with hydrogen: When group 16 elements combine with hydrogen they form hydrides with general formula H2

The hydrides formed are:


All of them have bent geometry with sp3 hybridization. The geometry shown by them is:


Structure of water


The properties of hydrides are:

  • Bond angle: The bond angle decreases down the group. The order of decrease of angle is:


The reason behind this is that when size of central atom increases, lone pair will push closer to bond pair-bond pair. Due to this bond angle decreases.

  •  Basic character: It refers to ability of molecule to donate its lone pair. The order of increase in basic character is:


  • Stability: The stability of hydrides depends upon the comparability of size. The order of stability of hydrides is:

Due to increase in size, bond length increase due to which bond dissociation energy decrease therefore stability decrease.

  • Reducing nature: The order of reducing character of hydrides are:

Out of them in case of H2Te the bond strength is low therefore reducing character is lowest.


  • Boiling point: The boiling point depends upon Vander wall force and this Vander wall force increases with increase in size.

The order of their boiling points for 15 group hydrides is:


In case of H2O and H2S, water has higher boiling point than hydrogen sulphide because of hydrogen bonding.


  1. Reaction with halogen: They react with halogen to form halides of formula EX4 , EX6 and EX2.

The order of stability oh halides are:


The group 16 elements react with iodine to form tetra iodides.

  • Oxygen only forms halides OF2 and O2F Out of them oxy difluoride is most stable halide.
  • Sulphur forms SCl2 (sulphur dichloride), SF6 (sulphur hexafluoride) and SF4 (sulphur tetra fluoride).
  • The geometry of SF4 is tetrahedral with hybridization sp3d and geometry of SF6 is trigonal bipyramidal with hybridization sp3d2 as shown:

       Class_12_Group_16_Chemical_Properties_Structure_Of_Sulphur_Tetrafluoride    Class_12_Group_16_Chemical_Properties_Structure_Of_Sulphur_Hexafluoride

Sulphur tetrafluoride                         Sulphur hexafluoride 

Hexa halides are only formed by fluorine because as size increases, coordination number decreases, therefore others they will not form halides .

  • Out of all halides sulphur hexahalide is most non reactive halide in this group because it has excess octet .So, no vacant d orbital is present moreover it is protected from all sides by fluorine .

3. OxO acids of sulphur

Some important oxo acids of sulphur are:

  • Sulphurous acid: it is reducing in nature.
  • It acts as oxidizing and reducing action.
  • It bleaches the articles due to reduction.
  • Its structure is given :


                  Sulphurous acid

(b)Sulphuric acid:

  • It is called king of chemicals.
  • It is used as an acid, oxidizing agent, dehydrating agent etc.
  • It is highly viscous due to hydrogen bonding.
  • It is also called as brown oil of vitrol.
  • It is further concentrated and form rectified oil.
  • It is prepared by contact process.
  • Its structure is given below:


   Sulphuric acid


(c)Thiosulphurous acid

  • It contains double bond between S atoms.
  • Its structure is given below:


           Thiosulphurous acid

(d)Thiosulphuric acid:

  • It contains one double bond S linkage between S atoms.
  • Its structure is given below:


          Thiosulphuric acid

(e)Dithionous acid

  • It contains one S-S bond.
  • Its structure is given:


     Dithionous acid

(f)Pyrosulphuric acid

  • It is known as oleum.
  • It contains one S-S linkage.
  • Sulphur dissolves in oleum to give clear brightly colored solution which contains polyatomic sulphur cations of general formula S42-.
  • The color of solution depends upon the time of reaction and strength of oleum.
  • The bright yellow color solution has S2-4 ions, deep blue solution S82+ and bright red solution has totally unexpected S2+19
  • Its structure is given below:


  Pyrosulphuric acid

(g)Dithionic acid:

  • It contains one S-S bond.
  • Its structure is given below:


Dithionic acid

(h)Peroxymonosulphuric acid:

  • It contains one peroxo group, it is also known as Caro’s acid.
  • It contains one peroxo group.
  • In it the oxidation state of S is +6.
  • Its structure is given below.


         Peroxymonosulphuric acid

Share these Notes with your friends  

< Prev Next >

You can check our 5-step learning process