The names transition metals and inner transition
metals are often used to refer to the elements of
d-and f-blocks respectively.
Zn , Cd and Hg are usually not considered as
transition elements due to the absence of
unpaired elements in d orbital
The transition elements show variable
oxidation state due to small energy
difference between (n-1)d &ns orbital
as a result both (n-1)d &ns electrons
take part in bond formation.
The high melting points of these metals are attributed to the
involvement of greater number of electrons from (n-1)d in
addition to the ns electrons in the interatomic metallic
bonding. In any row the melting points of these metals rise to a
maximum at d5 except for anomalous values of Mn and Tc and
fall regularly as the atomic number increases.
Greater the number of valence electrons,
stronger is the resultant bonding.
Since the enthalpy of atomisation is an important
factor in determining the standard electrode
potential of a metal, metals with very high
enthalpy of atomisation
(i.e., very high boiling point) tend to be noble in
their reactions
The shielding effect of a d electron is not that effective, hence the
net electrostatic attraction between the nuclear charge and the
outermost electron increases and the ionic radius decreases.
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 result of the lanthanoid contraction is that the second and
the third d series exhibit similar radii (e.g., Zr 160 pm, Hf 159 pm)
and have very similar physical and chemical properties much more
than that expected on the basis of usual family relationship.
The unique behaviour of Cu, having a positive E, accounts for its
inability to liberate H2 from acids.
Only oxidising acids (nitric and hot concentrated sulphuric) react
with Cu, the acids being reduced. The high energy to transform
Cu(s) to Cu2+(aq) is not balanced by its hydration enthalpy. The
general trend towards less negative E values across the series is
related to the general increase in the sum of the first and second
ionisation enthalpies.
The value of E for Mn, Ni and Zn are more negative than
expected from the trend.
Paramagnetism arises from the presence of unpaired electrons, each
such electron having a magnetic moment associated with its spin
angular momentum and orbital angular momentum.
The magnetic moment is determined by the number of unpaired
electrons and is calculated by using the ‘spin-only’ formula, i.e.,
μ = n(n + 2)
where n is the number of unpaired electrons and μ is the magnetic
moment in units of Bohr magneton (BM).
POTASSIUM DICHROMATE:-Preparation: - It takes place in three steps-
•Conversion of chromite ore to sodium chromate.
•Conversion of sodium chromate to sodium dichromate.
•Conversion of sodium dichromate to potassium dichromate
Following reaction take place:-4 FeCr2O4+ 4 Na2CO3 +7O2
2Na2CrO4 + 2 H+
Na2Cr2O7 + 2 KCl
2 Na2CrO4+ 2Fe2O3 +8 CO2
Na2Cr2O7 + 2 Na+ + H2O
K2Cr2O7 + 2 NaCl
POTASSIUM PERMANGNATE:-Preparation: -It takes place in two steps:-
•Conversion of pyrolusite ore into potassium mangnate
•Conversion of potassium mangnate to potassium permanganate
Following reactions take place:-
2 MnO2 + 4 KOH + O2
3 MnO4
2-
+4H+
2 K2MnO4 + 2H2O
2 MnO4- +MnO2 +2H2O
LANTHANOIDS: ---
•The 14 elements after Lanthanum having atomic number
58 to 71 are collectively known as Lanthanoids.
•The general electronic configuration of these elements is
[Xe] 4f1-14, 5d0-1 ,6s2 .
•Most common oxidation state of these elements is +3,
but Ce shows +4, Eu +2, because they acquire stable
configuration.
•The size of Lanthanoids and its trivalent ion decreases from
La to Lu due to poor shielding of 4f electrons.
It is known as lanthanoids contraction.
ACTINOIDS:-•The 14 elements after Actinium having atomic number
90 to 113 are collectively known as Actinoids.
•The general electronic configuration of these elements is
[Rn] 5f1-14, 6d0-1 ,7s2.
•The size of actinoids and its trivalent ion decreases from
Ac to Lw due to poor shielding of 5f electrons.
It is known as actinoids contraction.
•The elements after U (92) are man made known as
transuranic elements.