These are Online Notes on "p-Block elements" (Chapter=>7 ) Part 3 for practice of CBSE BOARD, CBSE NEET, CSIR NET Chemical Sciences etc.32. Oxygen:
Preparation: 2KClO3 == Heat MnO2 ==> 2 KCl + 3O2
2H2O2(aq) === finely divided metals ==> 2H2O(l) + O2(g)
2Ag2O(s ) == Heat ==> 4Ag(s) + O2(g)
2HgO(s) ==Heat==> 2Hg(l) + O2(g)
2Pb3O4(s) ==Heat==> 6PbO (s) + O2 (g)
(Red Lead)
2PbO2(s) ==Heat==> 2PbO(s) + O2(g)
33. Oxides:
The compounds of oxygen and other elements are called oxides.
Types of oxides:
a. Acidic oxides: Non- metallic oxides are usually acidic in nature.
SO2 + H2O ===> H2SO3 (sulphurous acid)
b. Basic oxides: Metallic oxides are mostly basic in nature. Basic
oxides dissolve in water forming bases e.g.,
Na2O + H2O ===> 2 NaOH
K2O + H2O ===> 2 KOH
CaO + H2O ===> Ca(OH)2
c. Amphoteric oxides: They show characteristics of both acidic as
well as basic oxides.
Al2O3 + 6HCl(aq) ===> 2 AlCl3 (aq) + H2O
Al2O3 + 6NaOH(aq) + 3H2O(l) ===> 2 Na3[Al(OH)6] (aq)
d. Neutral oxides: These oxides are neither acidic nor basic.
Example: Co, NO and N2O
34. Ozone:
Preparation:
i. It is prepared by passing silent electric discharge through pure
and dry oxygen 10 – 15 % oxygen is coverted to ozone.
3O2(g) ===> 2 O2(g); ΔH = +142 KJ mol-1
Structure of Ozone: Ozone has angular structure. Both O = O bonds
are of equal bond length due to resonance.
35. Sulphur:
Sulphur exhibits allotropy:
a. Yellow Rhombic ( α - sulphur):
b. Monoclinic (β- sulphur):
α - suphur ==360K ==> β - Sulphur
At 369 K both forms are stable. It is called transition temperature.
Both of them have S8 molecules. The ring is puckered and has a crown
shape.
Another allotrope of sulphur – cyclo S6 ring adopts a chair form.
S2 is formed at high temperature (~ 1000 K). It is paramagnetic
because of 2 unpaired electrons present in anti bonding π* orbitals like
O2.
36. Sulphuric acid:
Preparation: By contact process
1/8 S8 + O2 ===> SO2
2SO2(g) + O2(g) == V2O5, =====> 2 SO3(g) ΔHo = -196 KJ mol-1 2 bar, 720K
Exothermic reaction and therfore low temperature and high pressure
are favourable
SO3(g) + H2SO4 =====> H2S2O7 (Oleum)
H2S2O7 + H2O ====> 2H2SO4
(96-98 %)
It is dibasic acid or diprotic acid.
It is a strong dehydrating agent.
It is a moderately strong oxidizing agent.
is dibasic acid or diprotic acid.
It is a strong dehydrating agent.
It is a moderately strong oxidizing agent.
GROUP 17 ELEMENTS
37. Atomic and ionic radii: Halogens have the smallest atomic radii in
their respective periods because of maximum effective nuclear charge.
38. Ionisation enthalpy: They have very high ionization enthalpy
because of small size as compared to other groups.
39. Electron gain enthalpy: Halogens have maximum negative electron
gain enthalpy because these elements have only one electron less than
stable noble gas configuration.
Electron gain enthalpy becomes less negative down the group because
atomic size increases down the group.
40. Eelctronegativity: These elements are highly electronegative and
electronegativity decreases down the group. They have high effective
nuclear charge.
41. Bond dissociation enthalpy:
Bond dissociation enthalpy follows the order Cl2 > Br2 > F2 > I2
This is because as the size increases bond length increases.
Bond dissociation enthalpy of Cl2 is more than F2 because there are
large electronic repulsions of lone pairs present in F2.
42. Colour: All halogens are coloured because of absorption of radiations in visible region which results in the excitation of outer electrons to higher energy levels.
43. Oxidising power: All halogens are strong oxidisinga gents because
they have a strong tendency to accept electrons.
Order of oxidizing power is F2 > Cl2 > Br2 > I2
44. Reactivity with H2:
Acidic strength: HF < HCl < HBr < HI
Stability: HF > HCl > HBr > HI
This is because of decrease in bond dissociation enthalpy.
Boiling point: HCl < HBr < HI < HF
HF has strong intermolecular H bonding
As the size increases van der Waals forces increases and hence boiling
point increases.
% Ionic character: HF > HCl > HBr > HI
Dipole moment: HF > HCl > HBr > HI
Electronegativity decreases down the group.
Reducing power: HF < HCl < HBr < HI
45. Reactivity with metals: Halogens react with metals to form halides.
Ionic character: MF > MCl > MBr > MI
Halides in higher oxidation state will be more covalent than the one in
the lower oxidation state.
46. Inter-halogen compounds: Reactivity of halogens towards other
halogens:
Binary compounds of two different halogen atoms of general formula
X X’n are called interhalogen compounds where n = 1, 3, 5, or 7
These are covalent compounds.
All these are covalent compounds.
Interhalogen compounds are more reactive than halogens because XX’
is a more polar bond than X-X bond.
All are diamagnetic.
Their melting point is little higher than halogens.
XX’ (CIF, BrF, BrCl, ICl, IBr, IF) (Linear shape)
XX’3 (CIF3, BrF3, IF3, ICl3) (Bent T- shape)
XX’5 – CIF5, BrF5, IF5, (square pyramidal shape)
XX’7 – IF7 (Pentagonal bipyramidal shape)
47. Oxoacids of halogens:
Fluorine forms only one oxoacid HOF (Fluoric (I) acid or hypofluorous
acid) due to high electronegativity.
Acid strength: HOCl < HClO2 < HClO3 < HClO4
Reason: HClO4 ===> H+ + (ClO4)-
most stable
Acid strength: HOF > HOCl > HOBr > HOI
This is because Fluorine is most electronegative.
GROUP 18 ELEMENTS:
48. Ionisation enthalpy: They have very high ionization enthalpy
because of completely filled orbitals.
Ionisation enthalpy decreases down the group because of increase in
size.
49. Atomic radii: Increases down the group because number of shells
increases down the group.
50. Electron gain enthalpy: They have large electron gain enthalpy
because of stable electronic configuration.
51. Melting and boiling point: Low melting and boiling point because
only weak dispersion forces are present.
52. XeF2 is linear, XeF4 is square planar and XeF6 is distorted octahedral.
KrF2 is known but no true compound of He Ne and Ar are known.
53. Compounds of Xe and F:
Xe + F2 ==673K, 1 bar ==> XeF2
Xe + 2F2 ==873K, 7 bar ==> XeF4
Xe + 3F2 ==573K, 60 - 70 bar ==> XeF6
XeF2, XeF4 and XeF6 are powerful fluorinating agents.
54. Compounds of Xe and O:
6XeF4 + 12 H2O ====> 4 Xe + 2 XeO2 + 24HF + 3 O2
XeF6 + 3 H2O ====> XeO3 + 6 HF
Click HERE for Online Notes on "p-Block elements" (Chapter=>7 )
Part 1
Click HERE for Online Notes on "p-Block elements" (Chapter=>7 )
Part 1
No comments:
Write comments