Group 16 Elements (Oxygen Family) - Practice Questions & MCQ

Some of the physical properties of Group 16 elements are given in Table 7.6. Oxygen and sulphur are non-metals, selenium and tellurium metalloids, whereas polonium is a metal. Polonium is radioactive and is short lived (Half-life 13.8 days). All these elements exhibit allotropy. The melting and boiling points increase with an increase in atomic number down the group. The large difference between the melting and boiling points of oxygen and sulphur may be explained on the basis of their atomicity; oxygen exists as diatomic molecule (O₂) whereas sulphur exists as polyatomic molecule (S₈).

Oxidation states and trends in chemical reactivity
The elements of Group 16 exhibit a number of oxidation states (Table 7.6). The stability of -2 oxidation state decreases down the group. Polonium hardly shows –2 oxidation state. Since electronegativity of oxygen is very high, it shows only negative oxidation state as –2 except in the case of OF2 where its oxidation state is +2. Other elements of the group exhibit +2, +4, +6 oxidation states but +4 and +6 are more common. Sulphur, selenium and tellurium usually show + 4 oxidation state in their compounds with oxygen and +6 with fluorine. The stability of +6 oxidation state decreases down the group and stability of +4 oxidation state increases (inert pair effect). Bonding in +4 and +6 oxidation states is primarily covalent.

• Reactivity with hydrogen: All the elements of Group 16 form hydrides of the type H₂E (E=O, S, Se, Te, Po). Their acidic character increases from H₂O to H₂Te. The increase in acidic character can be explained in terms of decrease in bond enthalpy for the dissociation of H–E bond down the group. Owing to the decrease in enthalpy for the dissociation of H–E bond down the group, the thermal stability of hydrides also decreases from H₂O to H₂Po. All the hydrides except water possess reducing property and this character increases from H₂S to H₂Te.

• Reactivity with oxygen: All these elements form oxides of the EO₂ and EO₃ types where E = S, Se, Te or Po. Ozone (O₃) and sulphur dioxide (SO₂) are gases while selenium dioxide (SeO₂) is solid. Reducing property of dioxide decreases from SO₂ to TeO₂; SO₂ is reducing while TeO₂ is an oxidising agent. Besides EO₂ type, sulphur, selenium and tellurium also form EO₃ type oxides (SO₃, SeO₃, TeO₃). Both types of oxides are acidic in nature

• Reactivity towards the halogens: Elements of Group 16 form a large number of halides of the type, EX₆, EX₄ and EX₂ where E is an element of the group and X is a halogen. The stability of the 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.