Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry

Chemistry: Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry

The document Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry is a part of the Chemistry Course Inorganic Chemistry.
All you need of Chemistry at this link: Chemistry

GROUP 16 (OXYGEN FAMILY)

(1) ATOMIC & PHYSICAL PROPERTIES

Element
O
S
Se
Te
Atomic Number8163452
Atomic Mass1632.0678.96122.6
Electronic configuration(He)2s2 3p4(Ne) 3s2 3p4
[Ar] 3d10 4s2 4p4

[Kr] 4d10 5s2 5p4
Covalent Radius/pm74103119142
Ionization enthalpy (kJ mol–1)1314133941869
Electronegativity3.52.442.482.01
Boiling Point/K907189581260

(2) ABUNDANCE IN THE EARTH CRUST: O > S > Se > Te

(3) PHYSICAL STATE

Oxygen is gas while other are solids at room temperature. Oxygen exists as diatomic molecule where as other elements e.g. sulphur exists as shown into the following crown shape (puckered ring structure S8)

(4) METALLIC ACID NON-METALLIC CHARACTER

Metallic character increases with increase in atomic number.

Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry

(5) OXIDATION STATES

  • Oxygen shows-2 oxidation state in most of its compounds (being highly electronegative). Exception, in OF2 & O2F2 oxidation state of oxygen is +2 and +1 
  • Sulphur shows –2, +2, +4 and +6 oxidation states. Availability of +4 and + 6 oxidation states are due to the presence of empty d-orbitals. 
  • Sulphur shows higher oxidation states with compounds of oxygen and fluorine (h ighly electronegative elements( (SO2, SO3, SF4, SF6
  • The tendency to show –2 oxidation state decreases down the group since the electronegativity decreases.

(A) Oxygen (O)

If differs from the remaining element of the VIth group because of the following properties (A) Small Size (B) High electronegativity (C) Non-availability of d-orbitals.

(i) Preparation

1. 2HgO Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry 2Hg + O2

2Ag2O Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry 4Ag + O2

2. 2NaNO3Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry 2NaNO2 + O2

2KClO3Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry 2KCl + 3O(laboratory method)

3. 4K2Cr2OGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry 4K2CrO4 + 2Cr3O3 + 3O2

2KMnO4Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry K2 MnO4 + MnO2 + O2

(ii) Physical Properties

Colourless, odourless and tasteless gas. It is paramagnetic and exhibits allotropy. Three isotopes of oxygen are Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry Oxygen does not burn but is a strong supporter of combustion. 

(iii) Chemical Properties

(a) OXIDES 

(a-i) Acidic oxides.

Oxides of Non-metals and metals in highest oxidation state.

They dissolve in water forming oxyacids. e.g. CO2, SO2, N2O3, P4O6, P4O10, Cl2O7, CrO3, Mn2O7 etc.

Ex.: Cl2O7 + H2O → 2HClO4

SO3 + H2O → H2SO4

(a-ii) Basic oxides (Oxides of metals) 

They either dissolve in water to form alkalies or combine with acids to form salts and water or combine with acidic oxides to form salts.

Li2O, Na2O, BeO, MgO, CaO, SrO, BaO, CuO, FeO etc.

Na2O + H2O→2NaOH

(a-iii) Natural Oxides (Oxides of Non metals)

The neither combine with acids nor with the bases to form salts e.g. CO, N2O, NO, H2O etc.

(a-iv) Amphoteric oxides (Metal oxides)

These can combine with acid as well as bases e.g. ZnO, Al2O3, BeO, Sb2O3, Cr2O3, PbO, PbO2, etc.

PbO + 2NaOH→Na2PbO2 + H2O;

PbO + H2SO4 →PbSO4 + H2O

(a-v) Peroxides (Metal oxides)

They react with dil. Acids and form H2O2, e.g. Na2O2, K2O2, BaO2 etc.

Na2O2 + H2SO4→Na2SO4 + H2O2

(a-vi) Dioxides (metal oxides)

Like peroxide they contain excess of oxygen but do not yield H2O2 with dil. Acids e.g. PbO, MnO2 etc. They evolve Cl2 with conc. HCl and O2 with conc. H2SO4.

MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O

(a-vii) Super Oxides (metal oxides)

They contain O2 ion, e.g. KO2, RbO2 and CsO2. These oxides react with water forming H2O2 and O2 2KO2 + 2H2O → 2KOH + H2O2 + O2

(a-viii) Sub Oxides

They contain less oxygen than expected from the normal valency of the elements e.g. C3O2, N2O, Pb2O, Hg2O etc.

C3O2 → O=C=C=C=O

(b) OZONE (O3)

(i) Preparation

It is prepared by passing silent electric discharge through pure and dry oxygen

Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry

O2 + O →O3;

ΔH = 245 kJ mol-1

Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry

(ii) Properties 

(a) Oxidising agent: Ozone is a strong oxidizing agent in acidic medium

O3 + 2H+ + 2e→ O2 + H2O; SRP = + 2.07 V (acidic medium)

O3 + H2O + 2e→O2 + 2OH; SRP = + 1.24 V (alkaline medium)

O3→O2 + [O]

E.g.

1. 2KI + H2O + [O]→2KOH + O2 + I2

2. KI + 3O3→KIO3 + 3O2

3. S + 3O3 + H2O→H2SO4 + 3O2

4. 2I+ 9[O3]→I4O9 + 9O2

  • I2O9 yellow solid has the composition I+3 (IO–3)3. Formation of this compound is a direct evidence in favour of basic nature of I2 (i.e. its tendency of form cations)

O+ H2O2→2O+ H2O

5.Oxidising Redusing

agent  agent

TAILING OF MERCURY

Pure mercury is mobile liquid but when brought in contact with O3 its mobility decreases and it starts sticking to glass surface forming a type of tail due to the dissolution of Hg2O (mercury suboxide) in Hg.

  • O3 is used as a germicide and disinfectant for sterilizing water and improving the atmosphere of crowded places.

HYDROGEN PEROXIDE (H2O2)

(i) Preparation

(1) BaO2.8H2O + H2SO4(cold)→BaSO4 ↓ (white) + H2O2 + 8H2O

2) H2S2O8 + H2OGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry H2SO4 + H2SO5 Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry BaSO4 ↓ (white) + H2O2(aq)

Comparison (H2O & H2O2)

(i) Its boiling point 144 °C more than water but freezing point ( –4) less than water. Density a nd dielectric constant are higher than H2O.

(ii) Its aqueous solution is more stable than the anhydrous liquid where it decomposes into water and O2.

2H2O2→2H2O + O2

H2O2 is not kept in glass containers because traces of alkali metal ions from the glass can catalyzed the explosive decomposition of H2O2. Therefore, aqueous solutions is stored in plastic containers and some urea or phosphoric acid or glycerol is added to that solution because these compounds have been found to behave as negative catalyzed for the decomposition of H2O2.

(iii) Acidic nature

Behaves as a weak acid according to the following equation

Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry

Aqueous solution of H2Oturns blue litmusred which is then bleached by the oxidizing property of H2O2.

Na2CO3 + H2O3→Na2O2 + H2O + CO2

Ba(OH)2 + H2O2 + 6H2O→BaO2.8H2O↓

A 30% H2O2 solution has pH = 4.0

(iv) Oxidizing Agent

2e + 2H+ + H2O2→2H2O; SRP = 1.77 v (in acidic medium)

2e + H2O2 →2HO; SRP = 0.87 v (In alkaline medium)

On the basis of the above potentials, we can say that H 2O2 is strong oxidizing a gent in acidic medium but kinetically its is found that reactions are faster in basic medium.

Cr2O72– + 2H+ + 4H2O2→2CrO5 + 5H2O

CrO5 bright blue coloured compound is soluble in ether. 

Uses

(i) In bleaching of delicate materials such as silk, wool, cotton, ivory etc.

Properties of Hydrides

Table: Some Properties of H2O, H2S, H2Se and H2Te 


Enthalpies of formation (kJ mol–1)

Bond angle

Boling Point (C°)
H2O
–242
H—O—H = 108°28’
100
H2S–20
H—S—H = 92°
–60
H2Se
+81
H—Se—H = 91°
–42
H2Te
+154
H—Te—H = 90°
–2.3

The hydrides decreases in stability from H2O to H2Te. They become less stable because the bonding orbitals become larger and more diffuse hence overlap with the hydrogen ‘1s orbital’ is less effective.

The H—O—H bond angle in water is 104°28’, in accordance with the VSEPR prediction of slightly less than tetrahedral due to the presence of lone pairs of electrons. Thus the orbitals used for bonding by O are close to sp3 hybrids. In H2S to H2Te the bond angles become close to 90°.this suggests that almost pure p orbitals on Se and Te are used for bonding to hydrogen. In a series of similar compounds, the boiling points usually increase as the atoms become larger and heavier. If the boiling points increase, then the volatility decrease. This trend is shown by the boiling points of H2S. H2Se & H2Te, but the boiling point of water is anomalous. 

Water has an abnormally low volatility because its molecules are associated with each other by means f hydrogen bonds in both the solid and liquid states.

SULPHUR (S)

Sodium Thiosulphate (Na2S2O3.10H2O): (Hypo)

Preparation

(i)  Na2SO3S Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry Na2S2O3

Na2 SO3+ 2SO2 (excess)+ H2O→2NaHSO3+ CO ;

(ii) 2NaHSO3+ Na2CO3→2Na2S2O3+ H2O +CO2

Structure of Oxo acids of S

1. Sulphurous acid series

H2SO3 Sulphurous acidGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry
S(+IV)
H2S2Opyrosulphurou s acidGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry
S(+V), S(+III)
H2S2O4, dithionous acidGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - ChemistryS(+III)

2. Sulphuric acid series


H2SO4 Sulphuric acid
Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry
S(+IV)
H2S2O3 thiosulphuric acidGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry
S(+VI), S(–II)
H2S2O7 di or pyrosulphuric acidGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - ChemistryS(+VI)

3. Thionic acid series

H2S2O6 dithionic acidGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - ChemistryS(+VI)
H2SnO6 polythionic acid (n = 1 – 12)Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry

S(+V)

S(0)

4. Peroxoacid series

H2SO5 peroxomonosulphuric acidGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry
S(+VI)
H2S2O8 peroxodisulphuric acidGroup 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - ChemistryS(+VI)
The document Group 16 Elements: Oxygen Family Notes | Study Inorganic Chemistry - Chemistry is a part of the Chemistry Course Inorganic Chemistry.
All you need of Chemistry at this link: Chemistry
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