General characteristics of d-block elements
1 Atomic and Ionic Radii
The atomic and ionic radii of transition elements are
smaller than those of p- block elements and
larger than those of s-block elements. The atomic and ionic radii of first transition elements are given in the List.
Element and Atomic (pm) radii
Sc - 144
Ti - 132
V - 122
The atomic radii of first transition series decreases
from Sc to Cr and remains almost
constant till Cu and then increases towards the end. This can be explained based on two effects namely screening and
the nuclear charge effect. These two
effects oppose each other resulting in increase in nuclear charge.
Hence very slight variation in the atomic radii from Cr to Cu is observed.
It has been observed that Zirconium and Hafnium have
almost equal atomic radii. This is because
of lanthanide contraction.
transition elements are metals, since the number of electrons in the outermost shell is very small, being equal to 2. They are
hard, malleable and 3. Formation of
Most of the transition metal compounds are coloured in
their solid or solution form. The colour of
transition metal ions is due to the presence of unpaired electrons in it and the energy gap between two energy
levels in the same d-subshell
beingsmall. Hence very small amount of energy is required for excitation of electrons from one energy level to the other. The
energy can be easily provided by the visible light. The colour observed corresponds to
the complementary colour of the light
It may be noted that Zinc, Cadmium and Mercury salts do
not form any coloured compounds because of the absence of vacant d
orbitals to which electrons can be
excited. Sc3+ ions are also colourless because of the
absence of d-electrons.
4 Catalytic Properties
Most of the transition metals and their compounds are
used as catalyst.
The catalytic activity of transition metals is due to the
i) They show a variety of oxidation states and
thereby can form intermediate products with various reactants.
ii) They are also capable of forming interstitial
compounds which can adsorb and activate
the reacting species.
Some examples of catalyst are
i) Iron / molybdenum act as catalyst in the
synthesis of ammonia by Haber's Process.
ii) Vanadium pentoxide (V2O5) is used for catalytic oxidation of
SO2 to SO3
iii) TiCl4 is
employed as a catalyst in the manufacture of polythene.
5 Variable oxidation states
in their compounds. This property is due to the
elements have several (n - 1) d and ns electrons.
ii) The energies of (n - 1)d and ns orbitals are
fairly close to each other.
Salient features of oxidation states of transition
1. The elements which exhibit the maximum number of
oxidation states occur either in or near
the middle of the series. For example , in the first transition series manganese exhibits maximum number of oxidation
states (+2 to +7).
The elements in the
beginning of the series exhibit fewer oxidation states because they have less number of d-electrons which they
can lose or contribute for sharing. The
elements at the end of the series exhibit fewer oxidation states, because they have too many d electrons and hence fewer
vacant d-orbitals can be involved in bonding.
3. The transition elements in lower oxidation states (+2 and
+3) generally form ionic bonds and in
higher oxidation state form covalent bonds.
4. The highest oxidation state shown by any transition
metal is +8. For example, ruthenium and
osmium show highest oxidation states of +8 in some of their compounds.
metals show oxidation state of zero in their compounds. Ni(CO)4 and
Fe(CO)5 are common examples.
The magnetic properties of a substance are determined by
the number of unpaired electrons in it. There are two main type of
i) Paramagnetic substances
The paramagnetic character arises because of the presence
of unpaired electrons. Paramagnetic
substances are the substances which are attracted by magnetic field.
ii) Diamagnetic Substances
Diamagnetic character arises because of the absence of
Diamagnetic substance are the substances which are
repelled by the magnetic field.
Most of the transition elements and their compounds are
paramagnetic and are attracted by
magnetic field. Greater the number of unpaired electrons in the substance greater is the paramagnetic character, The
magnetic character of a substance is
expressed in terms of magnetic moments. The magnetic moment can be calculated using the relation
n(n + 2)BM (Bohr Magneton)
n = number of unpaired electrons
Ti3+ - The number of unpaired
electrons is 1. Hence
µ = 1(1+ 2)BM = 3 = 1.732 B.M
Larger the value of magnetic moment, the greater is the
In addition to paramagnetic and diamagnetic substance,
there are a few substances such as
iron which are highly magnetic as compared to ordinary metals. These substances are called ferromagnetic substances
7 Complex formation
The cations of d-block elements have strong tendency to
form complexes with certain
molecules (e.g. CO, NO, NH3....etc) or ions (e.g. F-, Cl-, CN- ....etc)
called ligands. Their tendency to form complexes is due to two reasons.
Small size and high positive charge density.
Presence of vacant (n-1)d orbitals which are of
appropriate energy to accept lone pair and
unshared pair of electrons from the ligands for bonding with them.
Examples of some complex compounds are,
[Cu(NH3)4]2+, [Ag(NH3)2]+, [Fe(CN)6]4-,....etc.
8 Formation of alloys
Transition metals form alloys with each other. This is
because they have almost similar size
and the atoms of one metal can easily take up positions in the crystal lattice
of the other. Eg. Alloys of Cr-Ni, Cr-Ni-Fe,