1. The d- Block Elements
By : A P Singh

3. 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

5. 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.

6. Group 7 Presentation

8. How are d - Block Elements & Transition elements different?
All d block elements are not transition elements but all transition elements are d-block 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.

9. Which of the d-block elements may not be regarded as the transition elements?
Why Zn, Cd and Hg are not considered as transition elements.
Why Scandium is a transition element but Zinc is not.
Copper atom has completely filled d orbital (3d10) in its ground state, yet it is transition element. Why
Silver atom has completely filled d orbital (4d10) in its ground state, yet it is transition element. Why
Why the very name ‘transition’ given to the elements of d-block .

10. Answers
Zn, Cd and Hg
Because they do not have vacant d-orbitals neither in the atomic state nor in any stable oxidation state.
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
Copper (Z = 29) can exhibit +2 oxidation state wherein it will have incompletely filled d-orbitals (3d), hence a transition element.
Silver (Z = 47) can exhibit +2 oxidation state wherein it will have incompletely filled d-orbitals (4d), hence a transition element.
The very name ‘transition’ given to the elements of d-block is only because of their position between s– and p– block elements.

11. 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

12. PHYSICAL PROPERTIES

13. 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

14. They have high enthalpies of atomisation
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.

15. Atomic & Ionic size

17. 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.

18. 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)

19. Ionization Enthalpies
IE2 :V < Cr > Mn and Ni < Cu > Zn
IE3 : Fe << Mn

20. Due to an increase in nuclear charge which accompanies the filling of the inner d- orbitals , There is an increase in ionization enthalpy along each series of the transition elements from left to right.
However, many small variations occur.

21. 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

22. 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.

23. Trends in the M2+/M Standard Electrode Potentials

24. 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.

25. Zinc sulfate
Hepta-
hydrate
Nickel(II)
nitrate
hexa-
hydrate
Titanium oxide
sodium
chromate
Potassium
ferricyanide
Vanadyl
Sulphate
dihydrate
Mangnaese(II)
chloride
tetrahydrate
Scandium
oxide
Cobalt(II)
chloride
Copper(II)
sulfate
penta-
hydrate

27. Splitting of d-orbital energies by an octahedral field of ligands

28. ES eg eg hv GS GS Do t2g t2g complex in electronic excited state (ES)
Ground State (GS)
d-d transition

29. An artist’s wheel

31. 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

32. CATALYTIC PROPERTIES This property is due to-
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.

33. iron(III) catalyses the reaction between iodide and per sulphate ions
For example
iron(III) catalyses the reaction between iodide and per sulphate ions
Explanation

34. 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.

35. 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

37. The paramagnetism first increases in any transition element series, and then decreases. The maximum paramagnetism is seen around the middle of the series.

38. Questions- Q. 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 Mn 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

39. 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–.

40. 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.

41. 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.

42. C Fe

43. The principal physical and chemical characteristics of these compounds are -:
high melting points, higher than those of pure metals.
very hard.
retain metallic conductivity.
chemically inert.

44. 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 < V2O4 < V2O5.
Less basic more basic amphoteric

45. 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

46. 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°.

47. In acidic solution,its oxidising action can be represented as follows:
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+ → 3Sn e–
b) 3 H2S → 6H+ + 3S + 6e– d) 6 Fe2+ → 6Fe e–

48. 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+

49. Properties
Oxidising Properties : Strong oxidising agent in acidic as well as in neutral
& basic medium :

51. Structure :

52. e) MnO4- (aq.)+S2O3--(aq.) + H2O(l) 
Questions for Practice
1. Complete the following reactions :
MnO4- (aq.) + C2O42-(aq) + H+(aq) >
Cr2O7-- + H2S + H >
Fe3+ + I >
CrO H >
e) MnO4- (aq.)+S2O3--(aq.) + H2O(l) 
Cr2O7-- (aq.)+ Fe2+ (aq.)+ H+ (aq.) 
g) KMnO4 ---->
h) Cu++ (aq) + I- (aq) >
i) Cr2O7-- (aq.)+ I- (aq.)+ H+ (aq.) ----->
j) 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

53. A. Explain the following :-
Cu(l) is not stable in an aq. solution.
With same (d4) configuration Cr(ll) is reducing whereas Mn (lll) is oxidising.
Transition metals are in general act as good catalyst.
Metal- metal bonding is more extensive in 4d & 5d series of transition metals than the 3d series.
Mn(lll) undergoes disproportionation reaction easily.
Co(ll) is easily oxidised in presence of strong ligands.
In a transition series of metals , the metals which exhibits the greatest No. of oxdn. occurs in the middle of the series .
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.
Transition metals and their compounds generally exhibits paramagnetic behaviour.

54. 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-- < MnO4-
16. 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.

55. 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.

56. Thanks