p - Block Elements Part - 3 | Class 12th

Ø Reactivity with Oxygen: All these elements form oxides of the EO₂ and EO₃ types where E = S, Se, Te or Po.

·       There are two types of oxides – simple oxides (e.g., MgO, Al₂O₃) and mixed oxides (Pb₃O₄, Fe₃O₄).

·       Simple oxides can be further classified on the basis of their acidic, basic or amphoteric character. An oxide that combines with water to give an acid is called acidic oxide (e.g., SO₂, Cl₂O₇, CO₂, N₂O₅).

·       Generally, non-metal oxides are acidic but oxides of some metals in higher oxidation states also have acidic character (e.g., Mn₂O₇, CrO₃, V₂O₅ etc.).

·       The oxide which gives an alkali on dissolved in water is known as basic oxide (e.g., Na₂O, CaO, BaO). Generally, metallic oxides are basic in nature.

·       Besides MO₂ type oxides sulphur, selenium and tellurium also form MO₃ type oxides (SO₃, SeO₃, TeO₃). Both types of oxides are acidic in nature. Increasing order of acidic nature of oxides is TeO₃ < SeO₃ < SO₃.

·       Some metallic oxides exhibit a dual behaviour. They show the characteristics of both acidic and basic oxides. Such oxides are known as amphoteric oxides. They react with acids as well as alkalis. E.g.: Al₂O₃, Ga₂O₃ etc.

·       There are some oxides which are neither acidic nor basic. Such oxides are known as neutral oxides. Examples of neutral oxides are CO, NO and N₂O.

·       SO₂ is a gas whereas SeO₂ is solid. This is because SeO₂ has a chain polymeric structure whereas SO₂ forms discrete units.

·       Reducing character of dioxides decreases down the group because oxygen has a strong positive field which attracts the hydroxyl group and removal of H⁺ becomes easy. 

 

Ø Reactivity Toward the Halogens: Elements of group 16 form a larger 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 halides decreases in the order F^- > Cl^- > Br^- > I^-. This is because E-X bond length increases with increase in size. 

·       Among hexa halides, fluorides are the most stable because of steric reasons.

·       Dihalides are sp³ hybridized and so, are tetrahedral in shape. 

·       Hexafluorides are only stable halides which are gaseous and have sp³d² hybridization and octahedral structure.