d- Block Elements

Report
*
By : A P Singh
Definition of d-block elements
 d-block elements:
The elements of periodic table belonging
to group 3 to 12 are known as d-Block
elements. because in these elements last
electron enters in d sub shell or d orbital .
 The d -block elements lies in between s- and
p-block elements in the long form of
periodic table
Transition Elements
A transition element is defined as the
one which has incompletely filled d
orbitals in its ground state or in any
one of its oxidation states. i.e.
A transition element should have
partially filled (n-1) d orbital.
Group 7 Presentation
How are d - Block Elements &
Transition elements different?
All d block elements are not transition
elements but all transition elements are dblock elements
All d block elements are not transition
elements because d block elements like
Zinc have full d10 configuration in their
ground state as well as in their common
oxidation state.which is not according to
definition of transition elements.
1. Which of the d-block elements may not be
regarded as the transition elements?
2. Why Zn, Cd and Hg are not considered as
transition elements.
3. Why Scandium is a transition element but Zinc
is not.
4. Copper atom has completely filled d orbital
(3d10) in its ground state, yet it is transition
element. Why
5. Silver atom has completely filled d orbital
(4d10) in its ground state, yet it is transition
element. Why
6. Why the very name ‘transition’ given to the
elements of d-block .
Answers
1.
Zn, Cd and Hg
2.
Because they do not have vacant d-orbitals neither in the
atomic state nor in any stable oxidation state.
3.
Scandium is a transition because it has incompletely filled d
orbitals in its ground state but Zinc have full d10
configuration in their ground state as well as in their common
oxidation state
4.
Copper (Z = 29) can exhibit +2 oxidation state wherein it will
have incompletely filled d-orbitals (3d), hence a transition
element.
5.
Silver (Z = 47) can exhibit +2 oxidation state wherein it will
have incompletely filled d-orbitals (4d), hence a transition
element.
6.
The very name ‘transition’ given to the elements of d-block is
only because of their position between s– and p– block
elements.
GENERAL & PHYSICAL PROPERTIES OF D-BLOCK ELEMENTS
 PHYSICAL PROPERTIES








ATOMIC & IONIC SIZE
IONIZATION ENTHALPY
OXIDATION STATES OF D-BLOCK ELEMENTS
COLOURED IONS
CATALYTIC PROPERTIES
MAGNETIC PROPERTIES
FORMATION OF COMPLEX COMPOUNDS
FORMATION OF INTERSTITIAL COMPOUNDS
PHYSICAL PROPERTIES
MELTING AND BOILING POINTS (ENTHALPIES OF ATOMISATION) :
melting and boiling
points are high.
A large number of
unpaired
electrons
take part in bonding
so they have very
strong metallic bonds
and hence high m.pt
& b.pt
They have high
enthalpies
of
atomisation . The
maxima is at about
the middle of each
series.
A large number of
unpaired electrons
take
part
in
bonding so they
have very strong
metallic bonds and
hence
high
enthalpy
of
atomization.
ATOMIC & IONIC SIZE
 Along the rows nuclear charge increases but
the penultimate d-sub shell has poor shielding
effect so atomic and ionic size remain almost
same .
 The radii of the third (5d) series are
virtually the same as those of the
corresponding members of the second
series.
 This
phenomenon is associated with the
intervention of the 4f orbital, the filling of
4f before 5d orbital results in a regular
decrease in atomic radii called Lanthanoid
contraction which essentially compensates
for the expected increase in atomic size with
increasing atomic number.
 The
net resultof the lanthanoid contraction is
that the second and the third d series exhibit
similar radii (e.g., Zr 160 pm, Hf 159 pm)
IONIZATION ENTHALPIES
IE2 :V < Cr > Mn and Ni < Cu > Zn
IE3 : Fe << Mn
 Due
to an increase in nuclear charge which
accompanies
the filling of the inner
dorbitals , There is an increase in ionization
enthalpy along each series of the transition
elements from left to right.
 However,
many small variations occur.
oxidation states
• Transition elements have variable oxidation
states ,due to very small energy difference
between (n-1)d & ns sub-shell electrons from
both the sub-shell take part in bonding
• The elements which give the greatest number of
oxidation states occur in or near the middle of the
series. Manganese, for example, exhibits all the
oxidation states from +2 to +7.
• Low
oxidation states are found when a complex
compound has ligands capable of π-acceptor character
in addition to the σ-bonding.
*For
example, in Ni(CO)4 and Fe(CO)5, the oxidation
state of nickel and iron is zero.
Trends in the M2+/M Standard Electrode Potentials
COLOURED IONS
Most of the transition metal compounds (ionic
as well as covalent) are coloured both in solid
state & in aqueous state.
Generally the elements/ions having unpaired
electrons produce coloured compound.
Titanium
oxide
Scandium
oxide
Vanadyl
Sulphate
dihydrate
sodium
chromate
Potassium
ferricyanide
Mangnaese(II)
chloride
tetrahydrate
Nickel(II)
nitrate
hexahydrate
Cobalt(II)
chloride
Zinc
sulfate
Heptahydrate
Copper(II)
sulfate
pentahydrate
Splitting of d-orbital energies by an octahedral field of ligands
ES
ES
eg
GS
eg
hv
t2g
complex in electronic
Ground State (GS)
t2g
d-d
transition
Do
GS
complex in
electronic
excited state
(ES)
An artist’s wheel
Questions:
Q1.Of the ions Ag+, Co2+ & Ti4+ which one will be
coloured in aqueous soln. ?
Q2. Why hydrated copper sulphate is blue while
anhydrous copper sulphate is white?
Q3.[Ti(H2O)6]3+ is coloured while [Sc(H2O)6]3+ is
colourless . Explain?
Q4. Why transtion metals & their compounds act as
good catalyst?
Q5. Why transtion metals generally forms coloured
compounds
CATALYTIC PROPERTIES
Vanadium(V) oxide,V2O5 (in Contact Process)
Finely divided iron (in Haber’s Process)
Nickel (in Catalytic Hydrogenation)
Cobalt (Synthesis of gasoline)
 This property is due to Presence of unpaired electrons in their
incomplete d orbitals.
 Variable oxidation state of transition metals.
 In most cases , provide large surface area with
free valencies.
For example
iron(III) catalyses the reaction between iodide
and per sulphate ions
Explanation
MAGNETIC PROPERTIES
When a magnetic field is applied to substances,
mainly two types of magnetic behaviour are
observed: diamagnetism and paramagnetism.
 Diamagnetic substances are repelled by the applied
field while the paramagnetic substances are
attracted.
 Substances which are attracted very strongly are said
to be ferromagnetic.


In fact, ferromagnetism is an extreme form of
paramagnetism.
Most of the transition elements and their compounds
show paramagnetism.
 Paramagnetism arises from the presence of unpaired
electrons, each such electron have a magnetic
moment.
 The magnetic moment of any transition element or its
compound/ion is given by (assuming no contribution
from the orbital magnetic moment).



μs = √n(n+2) BM
Here n is the number of unpaired electrons

The paramagnetism first increases in any transition
element series, and then decreases. The maximum
paramagnetism is seen around the middle of the series.
QUESTIONSQ. 1: Which ion has maximum magnetic moment
(a) V3+
(b) Mn3+
(c) Fe3+
(d) Cu2+
 Ans: c
 Q.2. What is the magnetic moment of Mn2+
ion (Z=
25) in aqueous solution ?
 Ans.- With atomic number 25, the divalent Mn2+ ion in
aqueous solution will have d5 configuration (five
unpaired electrons).Hence, The magnetic moment, μ
is

μ = √5(5 + 2) = 5.92BM

FORMATION
OF
COMPLEX COMPOUNDS

Complex compounds are those in which the metal
ions bind a number of anions or neutral molecules
giving complex species with characteristic
properties.

The transition metals form a large number of
complex compounds.

A few examples are: [Fe(CN)6]3–, [Fe(CN)6]4–,
[Cu(NH3)4]2+ and [PtCl4]2–.
This property is due to the
comparatively smaller sizes of the metal ions

their high ionic charges and the

availability of d orbitals for bond formation.
FORMATION OF INTERSTITIAL COMPOUNDS
 The
transition elements form a large number
of interstitial compounds in which small atoms
such as hydrogen, carbon, boron and nitrogen
occupy the empty spaces in their lattices.
 They
are usually non stoichiometric and are
neither typically ionic nor covalent,
 for
example, TiC, Mn4N, Fe3H, VH0.56 and
TiH1.7, etc.
C
Fe
The
principal
physical
and
chemical
characteristics of these compounds are -:
a) high melting points, higher than
pure metals.
b) very hard.
c) retain metallic conductivity.
d) chemically inert.
those of
Oxides and Oxoanions of Metals
All the metals except scandium form MxOy oxides which
are ionic.
As the oxidation number of a metal increases, ionic
character decreases.
In higher oxides, the acidic character is predominant
V2O2
Less basic
<
V2O4
more basic
<
V2O5.
amphoteric
Potassium dichromate K2Cr2O7
Preparation :
Dichromates are generally prepared from chromate, which in
turn are obtained by the fusion of chromite ore (FeCr2O4)
with sodium or potassium carbonate in free access of air.
4 FeCr2O4 + 8 Na2CO3 + 7 O2 → 8 Na2CrO4 + 2 Fe2O3 + 8 CO2
2Na2CrO4 + 2 H+
→ Na2Cr2O7 + 2 Na+ + H2O
Na2Cr2O7 + 2 KCl → K2Cr2O7 + 2 NaCl
Structure :
The chromate ion is tetrahedral whereas the dichromate
ion consists of two tetrahedra sharing one corner with
Cr–O–Cr bond angle of 126°.
Properties
Oxidising Properties
In acidic solution,its oxidising action can be represented as
follows:
Cr2O72– + 14H+ + 6e– → 2Cr3+ + 7H2O ;
e.g.
a) 6 I– → 3I2 + 6 e–
c) 3 Sn2+ → 3Sn4+ + 6 e–
b) 3 H2S → 6H+ + 3S + 6e–
d) 6 Fe2+ → 6Fe3+ + 6 e–
Potassium Permanganate, KMnO4
Preparation :
prepared by fusion of MnO2 with an alkali metal hydroxide
and an oxidising agent(O2 or KNO3) this produces the dark
green K2MnO4 which disproportionates in a neutral or acidic
solution to give permanganate.
2MnO2 + 4KOH + O2 → 2K2MnO4 + 2H2O
3MnO42– + 4H+ → 2MnO4– + MnO2 + 2H2O
 In the laboratory, a manganese (II) ion salt is oxidised by
peroxodisulphate to permanganate.
2Mn2+ + 5S2O82– + 8H2O → 2MnO4– + 10SO42– + 16H+
Properties
Oxidising Properties : Strong oxidising agent in acidic as well as in neutral
& basic medium :
Structure :
Questions for Practice
1. Complete the following reactions :
a) MnO4- (aq.) + C2O42-(aq) + H+(aq) ------->
b) Cr2O7-- + H2S + H+ ----->
c)
d)
e)
f)
g)
h)
i)
j)
Fe3+ + I- -------->
CrO4 2- + H+ ------>
MnO4- (aq.)+S2O3--(aq.) + H2O(l) 
Cr2O7-- (aq.)+ Fe2+ (aq.)+ H+ (aq.) 
KMnO4 ---->
Cu++ (aq) + I- (aq) -------->
Cr2O7-- (aq.)+ I- (aq.)+ H+ (aq.) ----->
MnO4- (aq.) + NO2-(aq) + H+(aq) ---->
2. What is meant by lanthanoid contraction ?
3. Describe the preparation of following compounds –
i. Potassium dichromate from Sodium chromate.
ii. KMnO4 from K2MnO4
A. Explain the following :1. Cu(l) is not stable in an aq. solution.
2. With same (d4) configuration Cr(ll) is reducing whereas Mn (lll) is
oxidising.
3. Transition metals are in general act as good catalyst.
4. Metal- metal bonding is more extensive in 4d & 5d series of
transition metals than the 3d series.
5. Mn(lll) undergoes disproportionation reaction easily.
6. Co(ll) is easily oxidised in presence of strong ligands.
7. In a transition series of metals , the metals which exhibits the
greatest No. of oxdn. occurs in the middle of the series .
8. Unlike Cr3+, Mn2+, Fe3+ & subsequent other M2+ ions of the 3d series
of the elements , the 4d and 5d series metals generally do not form
stable cationic species.
9. Transition metals and their compounds generally exhibits
paramagnetic behaviour.
10. Actinoids exhibits greater range of oxdn states than lanthenoids.
11. Transition metals generally forms coloured compounds .
12. Mn exhibits the highest oxdn state of +7 among the 3d series of
transition elements.
13. The enthalpy of atomisation of transition metals ar quite high.
14. There is a close similarity in physical & chemical properties of the
4d & 5d series of the transition metals , much more than the
expected on the basis of usual family relationship.
15. The oxidising power of oxoanions are in the order –
VO2+ < Cr2O7-- < MnO416. The third ionisation enthalpy of Mn is exceptionally high.
17. Cr 2+ is a stonger reducing agent than Fe 2+
18. La 3+ (Z= 57) and Lu3+(Z= 71) do not show any colour in solution
19. Among the divalent cations of the first transition series elements,
20. Mn exhibits the maximum paramagnetism .
21. Generally there is an increase in density of elements from Ti
(Z= 22) to Cu (Z= 29). in the 3d series of metals.
22. The atomic radii of the metals of third (5d) series of transition
metals are virtually the same as those of the corresponding
members of the second(4d) series.
23. The Eo value for Mn3+/ Mn2+ couple is much more positive than that
for Cr3+/Cr2+ couple or Fe3+/Fe2+ couple.
24. The highest oxdn state of a metal is exhibited in its oxides or
fluorides.
25. Zn is not regarded as a transition metal.
26. Explain why Ce4+ is a strong oxidising agent.
27. Many of the transition elements form interstitial compound
28. Lanthanoid form primarily +3 ions , while the actinoids have higher
oxdn statesin their compounds, +4 or even +6 being typical.
29. Co2+ is easily oxidised to Co3+ in the presence of a strong ligand.
30. CO is stronger complexing ligand than NH3 .
31. Mn2+ is much more resistant than Fe2+ towards oxdn.
32. The enthalpies of atomisation of transition metals are quite high.
33.There occur much more frequent metal-metal bonding in
compounds of 3rd (5d) transition series of d-block elements.
34. The Eo value for Cu2+/ Cu couple is positive in the 1st series
(rest have negative).
35. With the same d-orbital configuration (d4) Cr 2+ is a reducing agent
while M4+ is an oxidising agent.

similar documents