# Elements of p-Block II | Group 16 (Oxygen Family)

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Elements of p-Block II | Group 16 (Oxygen Family) – Ncert Elements of p-Block II | Group 16 (Oxygen Family)

Group-16 consists of oxygen [O], sulphur [S], selenium [Se], tellurium [Te] and polonium [Po] elements. This is known as chalcogen gorup.

The elements of group 16 have lower ionisation enthalpy values compared to those of group 15 in the corresponding periods, this is due to extra stable stable half filled p-orbitals in group 15 elements.

### General Characteristics of Elements of Group-16

• Electronic Configuration– Outer shell electronic configuration of elements of group- 16 is ns2np4.
• Ionisation Energy– The values of ionisation energy decreases down the group due to increasing size.

### Physical Properties of Elements of Group-16

• Melting and boiling points if the members of this group increases from top to bottom.
• Oxygen and sulphur are non-metals.
• All members of this family exhibit allotropy.
• Selenium and tellurium are metalloids.
• Oxygen exists as O2 (diatomic) whereas sulphur exists as S6 and S8.

### Anomalous behaviour of Oxygen-

1. Due to its small, size, high electronegativity, absense of d-orbitals and ability to form hydrogen bonding, oxygen show anomalous behaviour among the members of group-16.
2. Oxygen mainly show anomalous behaviour in the following respect.
• Reactivity to form oxides
• Reactivity with hydrogen
• Reactivity with halogens

### Method of preparation of oxygen

###### In laboratory, oxygen can be obtained by heating oxygen containing salts as chlorate, nitrate and permagnate.

${2KClO}_{3} \xrightarrow [{MnO}_{2}]{\Delta} {2KCl} + {3O}_{2} \uparrow$

### Properties of oxygen-

• Molecular oxygen is paramagnetic in nature.
• Oxygen atoms shows abnormal behaviour due to its smaller atomic size, higher electronegativity and absence of vacant d-orbitals in its valency sell.
• It combines or reacts with almost all metals and non-metals except some metals (Au, Pt) and nobel gases (He, Ne, Ar)

### Some important reactions

Dioxygen (O2) Preparation-

${2KClO}_{3} \xrightarrow [{MnO}_{2}]{ \Delta} {2KCl} + {3O}_{2}(g)$

${2PbO}_{2}(s) \longrightarrow {2PbO}(s) + {O}_{2}(g)$

${ 2H }_{ 2 }{ O }_{ 2 }{ (aq) }\longrightarrow { 2H }_{ 2 }{ O }{ (l)+ }{ { O }_{ 2 }{ (g) } }$

Catalytic property

${2SO}_{2} + {O}_{2} \xrightarrow {{V}_{2} {O}_{5}} {2SO}_{3}$

Ozone (O3) Preparation            ${3O}_{2} \longrightarrow {2O}_{3}$

Properties                            ${PbS}(s) + {4O}_{3}(g) \longrightarrow {PbSO}_{4}(s)+ {4O}_{2}(g)$

${ 2I }^{ - }(aq)+{ H }_{ 2 }{ O }(l)+{ O }_{ 3 }(g)\longrightarrow { 2OH }^{ - }(aq)+{ I }_{ 2 }(s)+{ O }_{ 2 }$

Sulphur Dioxide (SO2)-

Preparation- In laboratory SO2 can be obtained by the reaction of dilute sulphuric acid on copper sulphide.

${ SO }_{ 3 }^{ -2 }(aq)+{ H }^{ + }+(aq)\longrightarrow { H }_{ 2 }{ O }(l)+{ SO }_{ 2 }(g)$

### Physical and chemical properties

• Sulphur dioxide is a colourless gas with a pungent odour. It’s aqueous solution is acidic.
• Bleaching property of SO2 is temporary and based on reduction.

${SO}_{2} + {{2H}_{2}O} \longrightarrow {{H}_{2}{SO}_{4}} + \underset{Nascent Hydrogen}{2[H]}$

• In the presence of catalyst , it gets reduced into ${SO}_{3}$ by air, which is soluble in water.

#### Oxo-acids of sulphur

• Sulphur can form number of oxo-acids, such as H2SO3 , H2SO4, etc. These are acidic in nature.
• Acidic nature of an oxo-acid increases with the increase in positive oxidation state of sulphur in oxo-acids.

Lead chamber process– In lead chamber process, oxidation of SO2 is done by air in the presence of nitric oxide.

Contact Process- In contact process, oxidation of SO2 is done in the presence of Pt containing asbestos or vanadium pentoxide (V2O5).

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