p-block elements

Grade 12

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Dioxygen

Preparation-

Lab method-

2KClO3 2KCl + 3O2(heat,MnO2)

2. By thermal decomposition-

2Ag2O 4Ag + O2

2HgO 2Hg+O2

2Pb3O4 6PbO +O2

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3. 2H2O2 2H2O + O2 (MnO2)

4. Industrial method- From water or air. By electrolysis of water.

Properties-

1. 2Ca + O2 2CaO

2. 4Al + 3O2 2Al2O3

3. P4 + 5O2 P4O10

4. C + O2 CO2

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5. 2 ZnS + 3 O2 2ZnO + 2 SO2

6. CH4 + 2 O2 CO2 + 2 H2O

7. 2 SO2 + O2 2 SO3(V2O5)

8. 4 HCl + O2 2 Cl2 + 2 H2O

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Simple Oxides

A binary compound of oxygen with another element is called oxide.

Oxides may be simple or mixed.

Simple oxides may be acidic, basic or amphoteric.

Oxide + H2O Acid (Acidic Oxide)

Example- SO2, CO2

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SO2 + H2O H2SO3

Non- metal oxides are acidic but oxides of metals in high oxidation states also have acidic character. (e.g. Mn2O7, CrO3)

Oxide + H2O Base (Basic Oxide)

Examples- Na2O, CaO, BaO.

CaO + H2O Ca(OH)2

Metallic oxides are basic. Shipra Gupta

Some metallic oxides shows both acidic as well as basic character called as Amphoteric oxides.

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Ozone

Preparation-

When a slow dry stream of oxygen is passed through a silent electrical discharge conversion of oxygen to ozone occurs. The product is OZONISED OXYGEN.

3O2 2 O3 – Heat

This is Endothermic Reaction.

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Properties-

1. Powerful oxidizing agent.

O3 O2 + O

2. Oxidizes PbS to PbSO4 and I- to I2.

PbS + 4 O3 PbSO4 +4 O2

2 I- +H2O +O3 2OH- + I2 + O2

3. NO + O3 NO2 + O2

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Q. Though the formation of oxides with elements is exothermic, some external heating is required to initiate the reaction.

A. Bond dissociation enthalpy of O=O is very high. Q. The 2 O-O bond lengths in the ozone molecule are identical. A. Ozone is a resonance hybrid of 2 canonical structures.

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Sulphur-Allotropic Forms

Main allotropic forms are-

1. Yellow rhombic sulphur

2. Monoclinic sulphur

Sulphur forms yellow, rhombic crystals out of 8-membered rings of sulphur atoms (S8).

Sulphur forms yellow, monoclinic, needle-like crystals out of 8-membered rings of sulphur atoms (S8).

Plastic sulphur is yellow and made up of long chains of sulphur atoms. It reverts to S8 rings in time.

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Sulphur Dioxide

Preparation-

1. Sulphur is burnt in air.

S + O2 SO2

2. Lab method- Treating SO3- with

H2SO4.

SO3- + 2 H+ SO2 + H2O

3. Industrial- As a by- product of roasting of sulphide ores.

4 FeS2 + 11 O2 2 Fe2O3 + 8SO2

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Properties-

1. Colourless gas with pungent smell.

2. Soluble in water.

3. SO2 + H2O H2SO3(sulphurous acid)

4. 2 NaOH + SO2 Na2SO3 + H2O

Na2SO3 + H2O + SO2 2 NaHSO3

5. SO2 + Cl2 SO2Cl2(sulphuryl chloride)

( +nce of charcoal )

2SO2 + O2 2SO3( V2O5,Oxidation)

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6. Moist SO2 behaves as reducing agent.

• Fe (iii) Fe (ii)

• Decolorizes acidified KMnO4 solution.

2Fe3+ + SO2 + 2H2O 2 Fe2+ + SO4

2- + 4 H+

5SO2 + 2 MnO4- + 2 H2O

5SO42- + 4 H+ + 2 Mn2+

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Oxoacids of Sulphur

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Sulphuric Acid

1. Manufacture- By Contact Process

i) S8+8 O2 8 SO2(burning sulphur)

4FeS2+11 O2 2 Fe2O3 + 8 SO2

(roasting of sulphur rich ore)

ii) 2SO2 + O2 2SO3+ HEAT(oxidn.) (V2O5 or Platinised asbestos)

iii) SO3 + H2SO4(conc.) H2S2O7

H2S2O7 +H2O 2H2SO4

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Properties-

1. Dissociation-

H2SO4 H2O + SO3

2. Acidic Nature-

H2SO4 H+ + HSO4

-

HSO4- H+ + SO4

2-

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3. As dehydrating agent-

i) Drying of gases-Gases which do not react with H2SO4 like CO2,SO2,Cl2.

ii) Charring-

C12H22O11 11 H2O + 12 C (conc.H2SO4)

4. Oxidizing Action-Strong oxidising agent.

Cu + 2H2SO4 CuSO4 + SO2 +2H20(conc.)

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Halogen Family

Electronic Configuration- ns2np5

Atomic and Ionic Radii- Increases as we move down the group.

Ionisation Enthalpy- Decreases down the group.

Electron Gain Enthalpy- Halogens have max. –ve electron gain enthalpy and it decreases down the group.

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Electronegativity- Decreases down the group.

Colour- Halogens are coloured. Colour deepens down the group.

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Oxidation States and Trends in Chemical Reactivity

All halogens exhibit -1 oxidation state.

Cl, Br and I exhibit +1, +3, +5 and +7 oxidation states.

F has absence of d- orbitals.

All halogens are highly reactive.

Reactivity decreases down the group.

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Anomalous Behaviour of Fluorine

Small size, highest electronegativity, low F-F bond dissociation enthalpy and non- availability of d- orbital.

Reactions of fluorine are Exothermic.

HF is liquid while others are gases.

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Reactivity towards Hydrogen

Form HX type.

The affinity for hydrogen decreases from fluorine to iodine.

Acidic strength increases from HF to HI.

Reducing character increases down the group.

Thermal stability decreases down the group.

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Reactivity towards Oxygen

Halogens forms oxides with oxygen but most of them are unstable.

Fluorine forms two types of oxides- OF2(+1) and O2F2(+2).

Only O2F2 is thermally stable

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Reactivity towards metals

Form Metal Halides.

Ionic character decreases from MF to MI.

The Halides in higher oxidation state will be more covalent than the one in lower oxidation state.

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Reactivity of Halogens with other Halogens.

Form inter- Halogen Compounds like XX`, XX3`, XX5`, XX7` [ where X= larger size Halogen and X` is smaller size Halogen]

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Chlorine

Preparation –

MnO2 + 4 HCl MnCl2 + Cl2 + 2 H2O(heat)(conc.HCl)

4NaCl + MnO2 + 4 H2SO4 MnCl2 + 4 NaHSO4 + 2 H2O + Cl2

2. 2KMnO4 +16 HCl 2 KCl + 2 MnCl2 + 8H2O + 5Cl2

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Manufacture of Cl2-

1. Deacon`s Process- By Oxidation

4 HCl + O2 2Cl2+2H2O (CuCl2,723K)

2. Electrolytic Process- By electrolysis of brine (conc. NaCl solution). Cl2 is liberated at anode.

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Properties of Chlorine

React with metals and non- metals to form chlorides.

1. 2 Al + 3 Cl2 2 AlCl3

2. P4 + 6 Cl2 4 PCl3

It has great affinity for hydrogen.

H2 + Cl2 2 HCl

H2S + Cl2 2 HCl + S

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Excess ammonia

8NH3 + 3Cl2 6NH4Cl +N2

Excess chlorine

NH3 + 3 Cl2 NCl3 + 3HCl

Cold and dilute NaOH

2NaOH + Cl2 NaCl + NaOCl(hypochlorite) + H2O

Hot and conc. NaOH

6NaOH + 3Cl2 5NaCl + NaClO3(chlorate) + 3H2O

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With dry slaked lime

2Ca(OH)2 + 2Cl2 Ca(OCl)2+CaCl2+ 2H2O

Substitution Reaction-

CH4 + Cl2 CH3Cl(sunlight)

Oxidizes Fe2+ to Fe3+ and SO3- to

SO42-

2FeSO4+H2SO4+Cl2 Fe2(SO4)3+2HCl

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Powerful bleaching agent.

Cl2 + H2O 2HCl + [O]

Coloured subs. + [O] Colourless subs.

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Hydrogen Chloride

Preparation-

1. Lab method-

NaCl+H2SO4(conc.) NaHSO4+HCl (420K)

NaHSO4 +NaCl Na2SO4+HCl (823K)

HCl can be dried by passing through conc. H2SO4.

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Properties-

1. Ionizes as-

HCl + H2O H3O+ + Cl-

2. NH3 + HCl NH4Cl

3. 3 conc. HCl +1 conc.HNO3 =Aqua Regia

It is used for dissolving platinum and gold.

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Au + 4H+ + NO3- + 4Cl- AuCl4

- + NO +2H2O

3 Pt + 16 H+ + 4 NO3- + 18 Cl- 3PtCl6

- + 4 NO +8 H2O

4. Na2CO3 + 2 HCl 2NaCl + H2O + CO2

NaHCO3 + HCl NaCl + H2O + CO2

Na2SO3 + 2HCl 2 NaCl + H2O +SO2

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Oxoacids of Halogens

OxidationState/Chlorine/Bromine/Iodine

+1/HClO Hypochlorous acid/HBrO Hypobromous acid/HIO Hypoiodous acid

+3/HClO2 Chlorous acid / - / -

+5/HClO3 Chloric acid / HBrO3 Bromic acid/HIO3 Iodic acid

+7/HClO4 Perchloric acid/HBrO4 Perbromic acid/HIO4 Periodic acid

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Due to high electronegativity and small size , Fluorine forms only one oxoacid , HOF known as Fluoric (I) acid or Hypofluorous acid.

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Oxoacids Chlorous Acid and Hypochlorous

Acid

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Oxoacids of Halogens- Perchloric Acid And Chloric Acid

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Inter - Halogen Compounds

Preparation-

1. Equal volume

Cl2 + F2 2ClF (437K)

2. Cl2 in excess

I2 + 3 Cl2 2 ICl3

3. Excess F2

Cl2 + 3 F2 2 ClF3 ( 573K )

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4. Equimolar

I2 + Cl2 2 ICl

5. Diluted with water

Br2 + 3 F2 2 BrF3

6. Excess Fluorine

Br2 + 5 F2 2BrF5

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Properties-

1. Covalent compounds.

2. More reactive than the constituent halogen ( A-X bond is relatively weaker than X-X bond).

3. Diamagnetic in nature.

4. Good oxidising agent.

5. Melting and Boiling point increases with increase in difference in electronegativity.

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Structure of Interhalogen Compounds

AX type: In AX type, A is the central atom and X is the bonded atom. In these type of compounds, both atoms share their electrons and form single covalent bond.

A----X

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In AX3 type, A is the central atom and

undergoes sp3d hybridisation in first excited

state and gives 5 hybrid orbitals. Out of

five, three are bonding electrons and two

are lone pairs. Since sp3d hybridisation, it

should be in Trigonal bipyramidal shape,

but due to the presence of two lone pairs,

structure is distorted to "T"-- shape.

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AX5type: In AX5, A undergoes Sp3d2

hybridisation. The shape of the molecule is

distorted octahedral or distorted square

pyramidal.

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AX7 type: A undergoes sp3d3 hybridisation,

and the shape of the molecule becomes

pentagonal bipyramidal.

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Group – 18 Elements

Electronic configuration- ns2np6

Atomic Radii- Increases down the group.

Ionisation Enthalpy- Very high. Decreases down the group.

Electron gain enthalpy- Do not accept electrons and have large +ve values of electron gain enthalpy.

M.P. and B.P.- Low melting and boiling points.

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Chemical Properties

1. Least reactive. The inertness is due to:

Stable closed shell electronic configuration.

Exceptionally high ionisation enthalpy.

Very low electron affinities.

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Xenon – Fluorine Compounds

Form 3 binary fluorides- XeF2 , XeF4 and XeF6.

Xe (excess) + F2 XeF2(673K,1 bar, Ni tube)

1:5 ratio

Xe +2F2 XeF4(873K,7 bar,Ni tube)

1:20 ratio

Xe +3F2 XeF6( 573K,60-70bar,Ni )

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XeF4 + O2F2 XeF6 + O2

2 XeF2 +2H2O 2Xe + 4 HF + O2

XeF2 +PF5 [XeF]+[PF6]-

XeF4 +SbF5 [XeF3]+[SbF6]

-

XeF6 + MF M+[XeF7]-

(M=Na,K,Rb,Cs)

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Structures

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