d_block_PPT[1].ppt [Autosaved].ppt

2
Introduction
• d-block elements
 locate between the s-block and
p-block
 known as transition elements
 occur in the fourth and subsequent
periods of the Periodic Table

3
period 4
period 5
period 6
period 7
d-block elements

4
Introduction
Transition elements are elements that
contain an incomplete d sub-shell (i.e. d1
to d9) in at least one of their oxidation
states in compounds.
3d0
3d10

5
Introduction
Cd and Zn are not transition elements
because
They form compounds with only one
oxidation state in which the d sub-shell
are NOT incomplete.
Cd  Cd2+ 4d10 Zn  Zn2+ 3d10

6
The first transition series
the first horizontal row of the d-block elements

7
Characteristics of transition elements
(d-block vs s-block)
1. Physical properties vary slightly with atomic
number across the series (cf. s-block and
p-block elements)
2. Higher m.p./b.p./density/hardness than
s-block elements of the same periods.
3. Variable oxidation states
(cf. fixed oxidation states of s-block
elements)

8
Characteristics of transition elements
4. Formation of coloured compounds/ions
(cf. colourless ions of s-block elements)
5. Formation of complexes
6. Catalytic properties

9
The building up of electronic configurations
of elements:
 Aufbau principle
 Pauli exclusion principle
 Hund’s rule
Electronic Configurations

10
• 3d and 4s sub-shells are very close to
each other in energy.
• Relative energy of electrons in sub-
shells depends on the effective nuclear
charge they experience.
• Electrons enter 4s sub-shell first
• Electrons leave 4s sub-shell first

11
Cu Cu2+
After ‘electrons’
left the atom
Relative energy levels of orbitals
in atom and in ion

12
• Valence electrons in the inner 3d orbitals
• Examples:
 The electronic configuration of
scandium: 1s22s22p63s23p63d14s2
 The electronic configuration of zinc:
1s22s22p63s23p63d104s2

13
Element Atomic number Electronic configuration
Scandium
Titanium
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
21
22
23
24
25
26
27
28
29
30
[Ar] 3d 14s2
[Ar] 3d 24s2
[Ar] 3d 34s2
[Ar] 3d 54s1
[Ar] 3d 54s2
[Ar] 3d 64s2
[Ar] 3d 74s2
[Ar] 3d 84s2
[Ar] 3d 104s1
[Ar] 3d 104s2
Electronic configurations of the first series of the
d-block elements

14
• A half-filled or fully-filled d sub-shell
has extra stability

15
d -Block Elements as Metals
Physical properties of d-Block elements :
 good conductors of heat and electricity
 hard
 strong
 malleable and ductile
• d-Block elements are typical metals

16
• Physical properties of d-Block elements:
 lustrous
 high melting points and boiling points
• Exceptions : Mercury
 low melting point
 liquid at room temperature and
pressure

17
• d-block elements
 extremely useful as construction
materials
 strong and unreactive

18
 used for construction and making
machinery nowadays
 abundant
 easy to extract
• Iron

19
• Iron
 corrodes easily
 often combined with other
elements to form steel
 harder and higher resistance to
corrosion

20
• Titanium
 used to make aircraft and space
shuttles
 expensive
Corrosion resistant, light, strong and
withstand large temperature changes

21
• The similar atomic radii of the
transition metals facilitate
 formation of substitutional alloys
 the atoms of one element to
replace those of another element
 modify their solid structures and
physical properties

22
• Manganese
confers hardness & wearing resistance to
its alloys
e.g. duralumin : alloy of Al with Mn/Mg/Cu
• Chromium
 confers inertness to stainless steel

23
Atomic Radii and Ionic Radii
• Two features can be observed:
1. The d-block elements have smaller
atomic radii than the s-block
elements
2. The atomic radii of the d-block
elements do not show much variation
across the series

24
Variation in atomic radius
of the first 36 elements

27
(i)  in nuclear charge
(ii)  in shielding effect (repulsion between e-)
(i) > (ii)
(i)  (ii)
(ii) > (i)

28
• At the beginning of the series
 atomic number 
 effective nuclear charge 
 the electron clouds are pulled
closer to the nucleus
 atomic size 

29
• In the middle of the series
 the effective nuclear charge
experienced by 4s electrons increases
very slowly
 only a slow decrease in atomic radius
in this region
 more electrons enter the inner
3d sub-shell
 The inner 3d electrons shield the
outer 4s electrons effectively

30
• At the end of the series
 the screening and repulsive effects
of the electrons in the 3d sub-
shell become even stronger
 Atomic size 

31
• Many of the differences in physical and
chemical properties between the d-block
and s-block elements
 explained in terms of their differences
in electronic configurations and
atomic radii
Comparison of Some Physical and
Chemical Properties between the
d-Block and s-Block Elements

32
1. Density
Densities (in g cm–3) of the s-block elements and
the first series of the d-block elements at 20C

33
• d-block > s-block
 1. the atoms of the d-block elements
are generally smaller in size
2. more closely packed
(fcc/hcp vs bcc in group 1)
3. higher atomic mass
1. Density

34
• The densities
 generally increase across the first
series of the d-block elements
 1. general decrease in atomic
radius across the series
2. general increase in atomic mass
across the series
1. Density

35
2. Ionization Enthalpy
Element
Ionization enthalpy (kJ mol–1)
1st 2nd 3rd 4th
K
Ca
418
590
3 070
1 150
4 600
4 940
5 860
6 480
Sc
Ti
V
Cr
632
661
648
653
1 240
1 310
1 370
1 590
2 390
2 720
2 870
2 990
7 110
4 170
4 600
4 770
K  Ca (sharp ) ; Ca  Sc (slight )

36
Element
Ionization enthalpy (kJ mol–1)
1st 2nd 3rd 4th
Cr
Mn
Fe
Co
Ni
Cu
Zn
653
716
762
757
736
745
908
1 590
1 510
1 560
1 640
1 750
1 960
1 730
2 990
3 250
2 960
3 230
3 390
3 550
3 828
4 770
5 190
5 400
5 100
5 400
5 690
5 980
Sc  Cu (slight ) ; Cu  Zn (sharp )

37
• The first ionization enthalpies of the
d-block elements
 greater than those of the s-block
elements in the same period of the
Periodic Table
 1. The atoms of the d-block
elements are smaller in size
2. greater effective nuclear charges

38
Sharp  across periods 1, 2 and 3
Slight  across the transition series

39
• Going across the first transition series
 the nuclear charge of the elements
increases
 additional electrons are added to
the ‘inner’ 3d sub-shell

40
• The screening effect of the additional
3d electrons is significant
• The effective nuclear charge experienced
by the 4s electrons increases very slightly
across the series
• For 2nd, 3rd, 4th… ionization enthalpies,
similar gradual  across the series are
observed.

41
Electron has to be removed from
completely filled 3p subshell
3d5
3d5
3d5
3d10
d10/s2

42
• The first few successive ionization
enthalpies for the d-block elements
 do not show dramatic changes
 4s and 3d energy levels are close to
each other

43
Difficult to remove e- from fully- or half-filled sub-shells
d5
Cr+
Mn2+
Fe3+

44
3. Melting Points and Hardness
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
d-block >> s-block
 1. both 4s and 3d e- are involved in the
formation of metal bonds
2. d-block atoms are smaller

45
K has an exceptionally small m.p. because it has an
more open b.c.c. structure.
1541 1668 1910 1907 1246 1538 1495 1455 1084 419

46
 Unpaired electrons are relatively
more involved in the sea of electrons
Sc Ti V Cr Mn Fe Co Ni Cu Zn
1541 1668 1910 1907 1246 1538 1495 1455 1084 419

47
 
3d 4s
Sc
  
Ti
   
V
1. m.p.  from Sc to V due to the  of
unpaired d-electrons (from d1 to d3)
1541 1668 1910 1907 1246 1538 1495 1455 1084 419

48
2.m.p.  from Fe to Zn due to the 
of unpaired d-electrons (from 4 to 0)
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
     
3d 4s
Fe
     
Co
     
Ni

49
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
3. Cr has the highest no. of unpaired
electrons but its m.p. is lower than V.
     
3d 4s
Cr
It is because the electrons in the
half-filled d-subshell are relatively
less involved in the sea of electrons.

50
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
4. Mn has an exceptionally low m.p.
because it has the very open cubic
structure.
Why is Hg a liquid at room conditions ?
All 5d and 6s electrons are paired up
and the size of the atoms is much
larger than that of Zn.

51
• The metallic bonds of the d-block
elements are stronger than those of the
s-block elements
 much harder than the s-block
elements
• The hardness of a metal dependent on
 the strength of the metallic bonds

52
Mohs scale : - A measure of hardness
Talc Diamond
0 10
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn
0.5 1.5 3.0 4.5 6.1 9.0 5.0 4.5 -- -- 2.8 2.5

53
• In general, the s-block elements
 react vigorously with water to form
metal hydroxides and hydrogen
4. Reaction with Water
• The d-block elements
 react very slowly with cold water
 react with steam to give metal oxides
and hydrogen

54
d-block compounds vs s-block compounds
A Summary : -
Ions of d-block metals have higher charge density
 more polarizing
 1. more covalent in nature
2. less soluble in water
3. less basic (more acidic)
e.g. Fe(OH)3 < Fe(OH)2 << NaOH

55
• One of the most striking properties
 variable oxidation states
Variable Oxidation States
• The 3d and 4s electrons are
 in similar energy levels
 available for bonding

56
• Elements of the first transition series
 react with other elements to form
compounds
 form ions of roughly the same
stability by losing different
numbers of the 3d and 4s electrons
Variable Oxidation States

57
Oxidation
states
Oxides / Chloride
+1
Cu2O
Cu2Cl2
+2
TiO VO CrO MnO FeO CoO NiO CuO ZnO
TiCl2 VCl2 CrCl2 MnCl2 FeCl2 CoCl2 NiCl2 CuCl2 ZnCl2
+3
Sc2O3 Ti2O3 V2O3 Cr2O3 Mn2O3 Fe2O3 Ni2O3 • xH2O
ScCl3 TiCl3 VCl3 CrCl3 MnCl3 FeCl3
+4
TiO2 VO2 MnO2
TiCl4 VCl4 CrCl4
+5 V2O5
+6 CrO3
+7 Mn2O7
Oxidation states of the elements of the first transition
series in their oxides and chlorides

58
Oxidation states of the elements of the first transition
series in their compounds
Element Possible oxidation state
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Element Possible oxidation state
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
+3
+1 +2 +3 +4
+1 +2 +3 +4 +5
+1 +2 +3 +4 +5 +6
+1 +2 +3 +4 +5 +6 +7
+1 +2 +3 +4 +5 +6
+1 +2 +3 +4 +5
+1 +2 +3 +4 +5
+1 +2 +3
+2

59
1. Scandium and zinc do not exhibit variable
oxidation states
• Scandium of the oxidation state +3
 the stable electronic configuration
of argon (i.e. 1s22s22p63s23p6)
• Zinc of the oxidation state +2
 the stable electronic configuration
of [Ar] 3d10

60
2. (a) All elements of the first transition
series (except Sc) can show an
oxidation state of +2
(b) All elements of the first transition
series (except Zn) can show an
oxidation state of +3

61
3. Manganese has the highest oxidation state
+7
E.g. MnO4
-, Mn2O7
Mn7+ ions do not exist.

62
The +7 state of Mn does not mean that
all 3d and 4s electrons are removed
from Mn to give Mn7+.
Instead, Mn forms covalent bonds with
oxygen atoms by making use of its half
filled orbitals
Mn
O
O
O
O-

63
Draw the structure of Mn2O7
Mn
O
O
O
O
Mn
O
O
O

64
3. Manganese has the highest oxidation state
+7
• The highest oxidation state
 not be greater than the total
number of the 3d and 4s electrons
 inner electrons (3s, 3p…) are not
involved in covalent bond formation

65
4. For elements after manganese, there is a
reduction in the number of possible oxidation
states
• The 3d electrons are held more firmly
 the decrease in the number of
unpaired electrons
 the increase in nuclear charge

66
5. The relative stability of various oxidation
states is correlated with the stability of
electronic configurations
• Electronic configurations with half-filled
or fully-filled sub-shell has extra stability
Stability : -
Ti4+(aq) > Ti3+(aq)
Ar [Ar] 3d1
Ti4+(g) < Ti3+(g)
o
hydration
H

 : Ti4+ > Ti3+

67
Stability : - Mn2+(aq) > Mn3+(aq)
[Ar] 3d5 [Ar] 3d4
Fe3+(aq) > Fe2+(aq)
[Ar] 3d5 [Ar] 3d6

68
Stability : -
Zn2+(aq) > Zn+(aq)
[Ar] 3d10 [Ar] 3d104s1

69
Ion
Oxidation state of
vanadium in the ion
Colour in
aqueous solution
V2+(aq)
V3+(aq)
VO2+(aq)
VO2
+(aq)
+2
+3
+4
+5
Violet
Green
Blue
Yellow
Colours of aqueous ions of vanadium of
different oxidation states

70
Ion
Oxidation state of
manganese in the ion
Colour
Mn2+
Mn(OH)3
Mn3+
MnO2
MnO4
2–
MnO4
–
+2
+3
+3
+4
+6
+7
Very pale pink
Dark brown
Red
Black
Green
Purple
Colours of compounds or ions of manganese in
different oxidation states

71
(a)
differernt oxidation states: (a) +2; (b) +3; (c) +4
(b) (c)
Mn2+(aq) Mn(OH)3(aq) MnO2(s)

72
(e)
(d)
differernt oxidation states: (d) +6; (e) +7
MnO4
2–(aq) MnO4
–(aq)

73
Oxidizing power of Mn(VII) depends on
pH of the solution
In an acidic medium (pH 0)
MnO4
–(aq) + 8H+(aq) + 5e– Mn2+(aq) + 4H2O(l)
= +1.51 V
In an alkaline medium (pH 14)
MnO4
–(aq) + 2H2O(l) + 3e– MnO2(s) + 4OH (aq)
= +0.59 V

74
The reaction does not involve H+(aq) nor OH(aq)
Why is the Eo of MnO4
 MnO4
2 Eo = +0.56V
not affected by pH ?
MnO4
(aq) + e MnO4
2 Eo = +0.56V

75
MnO2 is oxidized to MnO4
2 in alkaline medium
2MnO2 + 4OH + O2  2MnO4
2 + 2H2O
Preparing MnO4
 from MnO2
1. 2MnO2 + 4OH + O2  2MnO4
2 + 2H2O
2. 3MnO4
2 + 4H+  2MnO4
 + MnO2 + 2H2O
3. Filter the resulting mixture to remove MnO2

76
• Another striking feature of the d-
block elements is the formation of
complexes
Formation of Complexes

77
• Most of the d-block metals
 form coloured compounds
Coloured Ions
 due to the presence of the
incompletely filled d orbitals in the
d-block metal ions
Zn2+, Cu+(3d10), Sc3+, Ti4+(3d0)
Which aqueous transition metal ion(s) is/are
not coloured ?

78
Number of unpaired
electrons in 3d
orbitals
d-Block metal
ion
Colour in
aqueous solution
0
Sc3+
Ti4+
Zn2+
Cu+
Colourless
Colourless
Colourless
Colourless
1
Ti3+
V4+
Cu2+
Purple
Blue
Blue
Colours of some d-block metal ions in aqueous solutions

79
Number of unpaired
electrons in 3d
orbitals
d-Block metal
ion
Colour in
aqueous solution
2
V3+
Ni2+
Green
Green
3
V2+
Cr3+
Co2+
Violet
Green
Pink

80
Number of unpaired
electrons in 3d
orbitals
d-Block metal
ion
Colour in
aqueous solution
4
Cr2+
Mn3+
Fe2+
Blue
Violet
Green
5
Mn2+
Fe3+
Very pale pink
Yellow

81
Co2+(aq) Fe3+(aq)
Zn2+(aq)

82
In gaseous state,
the five 3d orbitals are degenerate
i.e. they are of the same energy level
In the presence of ligands,
The five 3d orbitals interact with the
orbitals of ligands and split into two groups
of orbitals with slightly different energy
levels

83
The splitting of the degenerate 3d orbitals of
a d-block metal ion in an octahedral complex
g
e
g
t2
2
2
2
y
x
z
d
,
d 
yz
xz
xy d
,
d
,
d
distributes along x and y axes
distributes along z axis
Interact more strongly with
the orbitals of ligands

84
• Criterion for d-d transition : -
presence of unpaired d electrons in
the d-block metal atoms or ions
d-d transition is possible for
3d1 to 3d9 arrangements
d-d transition is NOT possible for
3d0 and 3d10 arrangements

85
3d9 : d-d transition is possible


Cu2+

86
3d0 : d-d transition NOT possible
Sc3+

87
Potassium dichromate
It is prepared in two steps :
(i)First the chromite ore ( FeCr2O4) is fused with
Na2CO3 or K2CO3 in free access of air
4 FeCr2O4 + 8 Na2CO3 + 7O2 8 Na2CrO4
+ 2 Fe2O3
+ 8 CO2

88
STEP : 02
(ii) The yellow soln of sodium
chromate is filtered and acidified
with H2SO4 to give a soln. from
which orange sodium dichromate
can be crystallized.
2 Na2CrO4 + 2H+ Na2Cr2O7
+2Na+ + H2O

89
Potassium dichromate to Sodium
dichromate
Sodium dichromate is more soluble
than Potassium dichromate
therefore K2Cr2O7 is prepared by treating
Na2Cr2O7 with KCl.
Na2Cr2O7 + KCl K2Cr2O7 + 2NaCl

90
Chromate and Dichromate ions
CrO42-
Cr
O
O
O
O
2-
Chromate ion

91
Dichromate ion
Cr2O7
2-
2-
O
O
O
Cr
O
Cr
O
O
O
1260

92
Chemical properties
K2Cr2O7 and Na2Cr2O7 are strong
oxidising agents :
In acidic solution its oxidising action
can be represented as :
Cr2O7
2- +14H+ +6e- 2Cr3+ + 7 H2O
(E =1.33V)

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