Download Document

Ch.45 notes – P.1
Ch.45 – Transition metals
A. General features of d-block elements
1. Meaning of transition elements
*
First transition series :
Atomic No.
21
22
23
24
25
26
27
28
29
30
Symbol
*
Electronic configurations of elements in first transition series :
At. no.
Name
Inner shell
21
Scandium
1s22s22p63s23p6
22
Titanium
1s22s22p63s23p6
23
Vanadium
1s22s22p63s23p6
24
Chromium
1s22s22p63s23p6
25
Manganese 1s22s22p63s23p6
26
Iron
1s22s22p63s23p6
27
Cobalt
1s22s22p63s23p6
28
Nickel
1s22s22p63s23p6
29
Copper
1s22s22p63s23p6
30
Zinc
1s22s22p63s23p6
3d
4s
* The d-block element is so called because its members have atoms with
electronic
configurations in which the d-orbitals are being filled.
* Sometimes, d-block elements or transition elements are also defined as
elements which form compounds in which there is an ______________
________
subshell
of d electrons in at least one of its compounds. (Such
definition effectively excludes scandium and zinc from the list of transition
elements.)
Ch.45 notes – P.2
2. Transition elements as metals
* d-electrons are involved in the metallic bond formation in the case of transition
metals, therefore they have
s-block metals.
metallic bond than
Such characteristics make transition metals extremely useful
as structural metals.
* The _______________________ of the transition metals make it possible for
atoms of one element to replace those of another element in the formation of
alloys .
It is possible to make alloys containing transition elements in a wide
range of composition.
The solid structure is slightly deformed but this is
sufficient to modify the physical properties of the structural material, e.g.,
manganese is well-known for conferring hardness and wear resistance to its
alloys, and chromium is responsible for conferring passivity on stainless steels.
*
Some uses of transition metals
 Titanium is used in the construction of the hull of the space shuttle and
aircraft
 Coinage metal is an alloy of copper and nickel.
 The bumpers of vehicles are chromium plated, giving shiny appearance.
 Pure titanium is not rejected by the body and has been used in replacing
missing human teeth with great success.
 Copper is used for cooking ware, electrical cables and water pipes.
 Iron is the most important structural metal ever used
Ch.45 notes – P.3
3. Comparison of some properties of d-block and s-block metals
a) Atomic radii
*
Variation of atomic radius with atomic number :
C.C.Lee/196 (3 inches)
*
Atomic radii (nm)
s-block
Li
Be
0.152 0.112
Na
Mg
0.190 0.160
K
Ca
d-block
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
0.235 0.197 0.164 0.147 0.135 0.130 0.135 0.126 0.125 0.125 0.128 0.137
Rb
Sr
0.248 0.215
Cs
Ba
0.267 0.222
Ch.45 notes – P.4
*
Two features :
(1) d-block metals generally have
atomic radii than
s-block metals.
(2) d-block metals show considerable ________________ in atomic radius
across the series.
As one looks at the trend of variation in greater details, it can be seen
that the atomic radii of the elements at first _____________ , then
remain ____________
in the middle of the series. At the end of the
series, the atomic radii actually ____________again.
At the beginning of the series, the increase in __________
_______________ with atomic number pulls in the electron cloud,
resulting in a reduction of atomic size.
Since electrons are added to an inner d subshell across the series, this
adds to the primary ______________ and ___________________ of
the 3d subshell, so that the effective nuclear charge increases only very
slowly in the middle of the row.
As a result, there is little change in
atomic radii in the middle range.
Towards the end of the series, the screening and repulsive effects of
the 3d electrons reach a maximum, resulting in an _______________
of the electron cloud.
b) Densities
*
Values of densities of s-block and d-block metals (in g cm-3)
s-block
Li
Be
0.53
1.850
Na
Mg
0.97
1.75
K
Ca
0.86
1.55 3.00 4.50 6.11 7.14 7.43 7.87 8.90 8.91 8.95 7.14
Rb
Sr
1.53
2.54
Cs
Ba
1.87
3.60
d-block
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ch.45 notes – P.5
*
Densities of d-block metals are much
than those of
s-block metals because
(1) d-block metals have ______________ atomic sizes
(2) d-block metals have _________________ structures
c) Melting points and hardness
* Melting points / ℃
s-block
*
d-block
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
64
850
1540 1675 1900 1890 1240 1535 1492 1453 1083 420
Melting points and hardness of d-block metals are _____________ than
s-block metals because
(1)
the
atomic
radii
relatively
(2)
d-block metals usually have
of
d-block
metals
are
.
a
______________
metallic
lattice structure.
(3)
_______________ electrons (including 4s and 3d electrons) are
involved in the metallic bond formation.
d) Ionization enthalpies
Ch.45 notes – P.6
*
The first ionization enthalpies of the d-block metals are ___________ than
those of s-block metals, since the atomic radii of d-block metals are
____________.
* The second ionization enthalpies of the d-block metals are ________ than
Group I metals but still __________ than Group II metals.
*
The third ionization enthalpies of d-block metals are _________ than
those of s-block metals, which the electrons are removed from the
___________________.
* Along the d-block metals, some abnormally high I.E. may be found:
(1) First I.E. of _____.
(2) Second I.E. of _____ and _____ .
(3) Third I.E. of _____.
(4) Fourth I.E. of _____.
Ch.45 notes – P.7
e) Electronegativities
*
Variation of electronegativities among the s-block metals and the d-block
metals :
s-block
Li
Be
1.0 1.6
Na Mg
0.9 1.3
K
Ca
0.8 1.0
Rb
Sr
0.8 1.0
Cs
Ba
0.8 0.9
*
Sc
1.4
Ti
1.5
V
1.6
Cr
1.6
d-block
Mn Fe
1.5 1.8
Co
1.8
Ni
1.8
Cu
1.9
E.N. of d-block metals are______________ than those of s-block metals
due to difference in _________________________.
f) Reactions with water
*
s-block metals reacts vigorously with water giving hydrogen gas.
d-block metals in general react only very slowly with cold water.
*
M(s)

M(g) 
Mn+(g)

Mn+(aq)
d-block metals are less reactive than s-block metals because
g)
(1)
d-block metals have
(2)
d-block metals have
metallic bond
I.E.
Oxidation state
* Except Groups IIIB (e.g. Sc) and Groups IIB (e.g. Zn), all d-block metals
exhibit _____________ oxidation states; while this is not the case for the
s-block metals.
i) Colour
* d-block compounds are often ____________; while s-block compounds are
_______________.
Zn
1.7
Ch.45 notes – P.8
B. Variable oxidation states of d-block elements
1. Oxidation states of the first row transition elements
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
+1
+3
+2
+2
+2
+2
+2
+2
+2
+2
+3
+3
+3
+3
+3
+3
+3
+3
+4
+4
+4
+4
+4
+4
+4
+5
+5
+5
+5
+5
+6
+6
+6
+2
+7
* Because the
3d
and
4s
electrons are of ___________ energy, both levels
of electrons are available for bonding. There is only a ____________________
in successive ionization energies of the d electrons. Thus when elements of the
first transition series react to form compounds, they can form ions of roughly
the ___________________ by losing different numbers of electrons.
* The higher oxidation states arise through ____________ bonding with more
electronegative elements such as fluorine, chlorine and oxygen, as in TiCl4 ,
-
CrO3 , MnO4 .
2. Oxidation states of vanadium
*
Vanadium forms four important oxidation states in aqueous solution.
VO3-(aq)

VO2+(aq)

VO2+(aq)

V3+(aq)
Fig. 43-6

V2+(aq)
Ch.45 notes – P.9
* Electrode potential values of interconversions between different oxidation
states of vanadium:
(
)
(
)
(
VO2+
VO2+
+ 1.0 V
)
(
V3+
+ 0.36 V
)
(
V2+
- 0.25 V
)
V
- 1.2 V
* Example: Refer to the following electrode potential – oxidation state chart and
electrode potential values.
a) What would be the final vanadium containing product if acidified ammonium
metavanadate solution (contains VO2+) is mixed with
1) potassium iodide solution.
2) potassium bromide solution..
3) copper powder.
4) excess aqueous sulphur dioxide.
b) In practice, the product obtained in (4) is blue rather than violet, Explain.
Ch.45 notes – P.10
3. Oxidation states of manganese
* The following table summarizes the species containing manganese at various
oxidation states:
Ion/Compound
MnO4-
Mn(OH)3 Mn2+
MnO42- MnO2
Oxidation state
Colour
Fig. 43-7
* Electrode potential values of interconversions between different oxidation
states of manganese in acidic medium:
(
MnO4-
) (
) (
MnO42+ 0.56 V
) (
Mn3+
MnO2
+ 2.26 V
) (
+ 0.95 V
) (
Mn2+
+ 1.51 V
)
Mn
- 1.18 V
+1.23V
+ 1.69 V
+ 1.51 V
* Electrode potential values of interconversions between different oxidation
states of manganese in alkaline medium :
(
MnO4-
) (
) (
MnO42+ 0.56 V
MnO2
+ 0.60 V
) (
) (
Mn(OH)3
- 0.20 V
) (
Mn(OH)2
+ 0.10 V
)
Mn
- 1.55 V
+ 0.59 V
* In acidic medium, ____________________ is very stable in the form of Mn2+.
It can be formed when manganese in any higher oxidation is reduced in acidic
medium.
Ch.45 notes – P.11
* Both __________ and ____________ are powerful oxidizing agents in acidic
medium to give Mn2+.
MnO2(s) + HCl(aq) 
MnO4-(aq)
+ Fe2+(aq) + H+(aq)

* In alkaline medium, however, the oxidizing power of MnO4- ion decreases, and
its is reduced to __________ only.
* Example:
1. Explain whether the following reaction is feasible or not:
a) Mixing of Mn(VII) compounds with Mn(IV) compounds to form Mn(VI)
compounds in acidic medium.
2 MnO4- + MnO2 + 2 H2O 
3 MnO42- + 4 H+
b) Mixing of Mn(VII) compounds with Mn(IV) compounds to form Mn(VI)
compounds in alkaline medium.
2 MnO4- + MnO2 + 4 OH- 
3 MnO42- + 2 H2O
c) Mixing of Mn(II) compounds with Mn(IV) compounds to form Mn(III)
compounds in acidic medium.
Mn2+ + MnO2 + 4 H+ 
2 Mn3+ + 2 H2O
Ch.45 notes – P.12
2. This question is concerned with the following electrode potentials:
a) Which of the above electrode potentials are dependent on pH?
b) Mn3+(aq) in neutral solution will disproportionate, write an equation for this
and explain why it is feasible.
C. Complex formation by d-block elements
1. Formation of complex ions/compounds
* A complex is formed when a transition metal atom (or ion) is surrounded by a
number of molecules or ions.
They are linked together by ________
covalent bond.
e.g.
* The transition metal atom (or ion) is called the _____________ ( or nuclear
atom ).
It must possess _____________ orbitals available for dative bond formation.
* The molecules or ions to which the central atom is bonded are called
___________. They must possess ______________ of electrons.
* Ligands may be _____________ or
tridentate
,
tetradentate , hexadentate
_______________,i.e. bidentate ,
, etc.
Ch.45 notes – P.13
* The number of ligands bonded to the central atom is called ______________
___________.
* The overall charge of the complex depends on the charges of the central atom
and the liqands, if any.
Co2+
e.g.
+
6 H2O

Fe3+
+
6 NH3

Fe2+
+
6 CN-

Cu2+
+
4 NH3

4 Cl-

Cu2+
Co3+
+
+
3 NH3 +
3 Cl-

* The strong tendency for the d-block metals to form such a large number of
stable complexes is due to two reasons:
(1) The ________ sizes and ________ charges of their ions.
(2) The availability of vacant _____________________________ to accept
lone pair electrons from ligands.
2. Nomenclature of complex compounds
*
[Rules]
(1) The cation is always named before the anion, no matter which part of the
compound is the actual complex.
(2) In naming the complex, the ligands are named before the central atom, and
immediately following the central atom is its oxidation state in Roman
numerals enclosed in brackets.
Ch.45 notes – P.14
(3) Names of some ligands :
ClBrOHCNNH3
H2O
CO
(4) The number of each type of ligand is specified by the Greek prefixes,
mono- , di- , tri- , tetra- , penta- and hexa- etc.
(5) For more than one type of ligands, they are arranged in the order of
anionic - neutral - cationic.
(6) For ligands of the same type, they are arranged in the alphabetical order of
the element symbols of the ligating atoms.
(7) Names for anionic complexes end in
'ate'
followed by Roman
numerals indicating the oxidation state of the central atom.
Metal
Name in Anionic Complex
Titanium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
Platinum
(8) Names for cationic complexes have no special ending.
(9) For a neutral complex compound, the name of the complex is the name of
the compound.
Ch.45 notes – P.15
*
[Examples]
[ Co(H2O)6 ]2+
[ Co(H2O)6 ] Cl2
[ Cu(NH3)4 ]2+
[ CoCl2(NH3)4 ]+
[ Fe(NH3)3 (H2O)3 ]2+
[ PtCl(NH3)5 ] Br
[ Fe(CN)6 ]3[ Fe(CN)6 ]4K4 [ Fe(CN)6 ]
[ CuCl4 ]2[ PtCl6 ]2[ CoCl3(NH3 )3]
[ Ni(CO)4]
* Ex. 1. Write the formulae of the following compounds:
a) chloropentaamminecobalt(III) chloride
b) ammonium hexachlorotitanate(IV)
c) dihydroxotetraaquairon(II)
2. Name the following compounds:
a) [Fe(H2O)6]Cl2
b) [Cu(NH3)4]Cl2
c) [PtCl4(NH3)2]
d) K2[CoCl4]
Ch.45 notes – P.16
3. Stereochemistry of complexes
a) Stereo-structures of complexes
(i) Tetrahedral structure
*
Tetra-coordinated
*
e.g.
*
[ Hybridization ] :
*
Not common for transition metals
[ Zn(NH3)4 ]2+ , [ CoCl4 ]2-
(ii) Square planar structure
*
Tetra-coordinated
*
e.g.
*
[ Hybridization ] :
[ Cu(NH3)4 ]2+ , [ NiCl4 ]2-
(iii) Octahedral structure
*
Hexa-coordinated
*
e.g.
*
[ Hybridization ] :
[ Co(NH3)6 ]2+ , [ Fe(CN)6 ]3- ,
Ch.45 notes – P.17
b) Isomerism
(i) Structural isomerism
*
e.g.
*
e.g.
(ii) Geometrical isomerism
*
e.g.
[ Pt Cl2 (NH3)2 ]
*
e.g.
[ Co Cl2 (NH3)4 ]+
*
e.g.
[ Co Cl3 (NH3)3 ]
Ch.45 notes – P.18
4. Stability of complexes
* Some ligands may form stronger bonds than other ligands with a particular
metal ion.The better ligand will displace the poorer one :
[ M (H2O)n ]
e.g.
nL
[ Cu(H2O)4 ]2+ +
K
st
* The
+

[ M Ln ]

4 NH3
[ Cu(NH3)4 ]2+
+
n H 2O
+ 4 H2O
of [ Cu(NH3)4 ]2+ =
equilibrium
constant
for
this
reaction
is
known
as
the
_______________________.
*
The larger the value of
K , the
st
*
Some values of stability constants :
stable the complex is.
Table 43-14
* The values of Kst are generally large. Thus, the complex ions of d-block metals
are generally very stable.
* Ex.:
Ch.45 notes – P.19
D. Coloured ions of d-block elements
* The majority of transition metal ions are coloured. The colours and the number of
3d electrons present in some hydrated ions are given below.
Fig. 43-10,11
Sc3+(aq)
Colourless
3d0
Fe3+(aq)
Yellow
3d5
Ti3+(aq)
Purple
3d1
Fe2+(aq)
Green
3d6
V3+(aq)
Green
3d2
Co2+(aq)
Pink
3d7
Cr3+(aq)
Violet
3d3
Ni2+(aq)
Green
3d8
Mn3+(aq)
Red
3d4
Cu2+(aq)
Blue
3d9
Mn2+(aq)
Pink
3d5
Zn2+(aq)
Colourless
3d10
* Complex ions of the same central atom but different ligands have different colours.
Colours of various complex ions formed by copper(II) ion are listed below :
*
*
[ Cu(H2O)4 ]2+
Blue
[ Cu(NH3)4 ]2+
Deep blue
[ CuCl4 ]2-
Yellow
The colour of transition metal complex ion is associated with :
(1)
an _________________________
(between
1
and
9
(2)
the nature of ______________ surrounding the central atom.
d
A free, isolated transition metal ion has originally all its five
electrons)
3d
orbitals
energetically equivalent, i.e. they are said to be _________________ .
*
Under the influence of a ligand (such as water molecule), the 3d
split into two groups with slightly different energy levels.
orbitals are
Ch.45 notes – P.20
* As sufficient light energy is absorbed from a white light source, the
is promoted from its lower to one of the higher
3d
orbitals.
3d electron
The resulting
d-d transition causes ____________________, and the remainder of the light
reflected in the visible spectrum accounts for the specific colour of that complex
ion.
(The absorbed energy is dispersed as heat, NOT
re-emitted as light.)
E. Catalytic properties of d-block elements and their compounds
1. Catalysts in industrial processes
*
V2O5 in Contact process
*
Finely divided iron powder in Haber process
*
MnO2 in the decomposition of hydrogen peroxide
*
Ni or Pt in hydrogenation of alkenes
2. Mechanism of catalytic action
a) Heterogeneous catalysis
*
The reactants of the reaction and the catalysts are of
e.g.
Fe powder used in Haber process
N2(g)
*
_______________.
+
3 H2(g) ====
2 NH3(g)
In the presence of a solid catalyst, at least one of the reacting gases is
________________on the solid surface, hence local concentrations are
increased. The adsorption also leads to ________________ of the bonds in
the molecules concerned. (Such weakening of the bonds in the reactant
molecules results in the
_________________________
of
the
reaction and makes the reaction faster). After formation, the products are
______________ from the surface of the solid catalyst.
*
The larger number of valence electrons and available orbitals in the atoms
of d-block elements facilitate the adsorption of reactants onto their
surfaces.
Ch.45 notes – P.21
b) Homogeneous catalysis
*
The catalyst, reactants and products are uniformly distributed in the
_____________________.
*
During catalysis of this type, the reaction takes place via a
______________________
consisting of two steps of which the
activation energies are lowered so the reaction is accelerated.
*
When a transition metal compound is added to a system of a redox
reaction, it is converted from one oxidation state to another and then
reverted to its original oxidation state.
e.g.
Given:
Fe(II) or Fe(III) used to catalyse the reaction :
S2O82-
*
+
2 I-

2 SO42-
+
I2
Transition elements and their compounds are good catalysts of this type
because they exhibit ___________________________ and enable the
redox
reactions to take place via two steps.