Summary
IUPAC defines transition
metal as an element whose atom has an incomplete d sub shell or which can give
rise to cations with an incomplete d sub shell. They occupy the central
position of the periodic table, between s and p block elements,
d- Block elements
composed of 3d series (4th period) Scandium to Zinc ( 10 elements), 4d series (
5th period) Yttrium to Cadmium ( 10 elements) and 5d series ( 6th period)
Lanthanum, Haffinium to mercury.
the general electronic
configuration of d- block elements can be written as [ Noble gas] ( n −1)d1−10 ns1−2
Here, n = 4 to 7 . In
periods 6 and 7, the configuration includes
( (n −2) f orbital ;
[Noble gas] ( n −2) f 14 ( n −1)d1−10 ns1−2 .
All the transition
elements are metals. Similar to all metals the transition metals are good
conductors of heat and electricity. Unlike the metals of Group-1 and group-2,
all the transition metals except group 11 elements are hard.
As we move from left to
right along the transition metal series, melting point first increases as the
number of unpaired d electrons available for metallic bonding increases, reach
a maximum value and then decreases, as the d electrons pair up and become less
available for bonding.
Ionization energy of
transition element is intermediate between those of s and p block elements. As
we move from left to right in a transition metal series, the ionization
enthalpy increases as expected.
The first transition
metal Scandium exhibits only +3 oxidation state, but all other transition
elements exhibit variable oxidation states by loosing electrons from (n-1)d
orbital and ns orbital as the energy difference between them is very small.
In 3d series as we move
from Ti to Zn, the standard reduction potential (E0 M2+/M)
value is approaching towards less negative value and copper has a positive
reduction potential. i.e., elemental copper is more stable than Cu2+.
Most of the compounds of
transition elements are paramagnetic. Magnetic properties are related to the
electronic configuration of atoms.
Many industrial
processes use transition metals or their compounds as catalysts. Transition
metal has energetically available d orbitals that can accept electrons from
reactant molecule or metal can form bond with reactant molecule using its d
electrons.
Transition metals form a
number of interstitial compounds such as TiC, ZrH1.92 , Mn4
N etc .
Transition elements have
a tendency to form coordination compounds with a species that has an ability to
donate an electron pair to form a coordinate covalent bond.
In the inner transition
elements there are two series of elements. 1) Lanthanoids ( previously called lanthanides) 2) Actinoids ( previously
called actinides)
Lanthanoids have general
electronic configuration [Xe] 4f 1−14 5d0−1 6s2
The common oxidation
state of lanthanoides is +3
As we move across 4f
series, the atomic and ionic radii of lanthanoids show gradual decrease with
increse in atomic number. This decrese in ionic size is called lanthanoid
contraction.
The electronic
configuration of actinoids is not definite. The general valence shell
electronic configuration of 5f elements is represented as [Rn]5f 2 −14 6d0 −2 7s2 .
Like lanthanoids, the
most common state of actinoids is +3. In addition to that actinoids show
variable oxidation states such as +2 , +3 , +4 ,+5,+6 and +7.
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