Group 16 Elements | Chemical Reactivity#

1. Reactivity with Hydrogen:#

Group 16 elements react with hydrogen to form hydrides of the type H₂E (E = O, S, Se, Te, Po).

Their acidic character increases from H₂O to H₂Te due to decrease in bond enthalpy of H-E bond down the group.
Thermal stability of hydrides decreases down H₂O to H₂Po due to decrease in bond dissociation enthalpy of H₂O to H₂Po.
All the hydrides except water possess reducing property and this character increases from H₂S to H₂Te.

Physical state: Ozone(O₃) and sulphur dioxide (SO₂) are gases while selenium dioxide (SeO₂) is solid.
Reducing property: Reducing property of dioxide decreases from SO₂ to TeO₂. SO₂ is a reducing agent while TeO₂ is an oxidizing agent.
Besides EO₂ type, sulphur, selenium and tellurium also form EO₃ type oxides (SO₃, SeO₃, TeO₃).
Acidic character: Both EO₂ and EO₃ type oxides are acidic in nature.

Elements of Group 16 form a large number of halides of the type: EX₆, EX₄ and EX₂, where E is an element of group 16 and X is a halogen.
The stability of halides decreases in the order F^- > Cl^- > Br^- > I^-. Amongst hexahalides, hexafluorides are the only stable halides. All hexafluorides are gaseous in nature They have octahedral structure. Sulphur hexafluoride, SF₆, is exceptionally stable for steric reasons.
Amongst tetrafluorides, SF₄ is a gas, SeF₄ is a liquid and TeF₄ is a solid. These fluorides have sp³d hybridisation. Their geometry is Trigonal bipyramidal and shape is see-saw.
All the elements except selenium form dichlorides and dibromides. These halides are formed by sp³ hybridisation and have tetrahedral structure.
The well known monohalides are dimeric in nature. These dimeric halides undergo disproportionation as below:

\[ 2Se_2Cl_2 → SeCl_4 + 3Se \]