p-block elements - class 12 a12aftw.weebly.com/uploads/5/0/4/6/50469687/p-block_elements_ppt… ·...
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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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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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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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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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