1) What are d-block elements? Give the properties of d-block elements?
The elements which have partially filled d-orbitals either in the ground state
or in one or more of their ions are called as d-block elements or outer
transition elements.They are all metals and have electronic configuration ns2,
(n-1)d1 to 10. Different properties shown by them are:
a. Metallic character: All transition elements are metals.
b. Oxidation state: They show variable state oxidation due to the small energy
difference in between (n-1)d and ns orbitals. Example: Cr : +1, +2, +3, +4, +5,
+6 and Mn : +2, +3, +4, +6, +7.
c. Atomic character: The atomic size of d-block elements decreases from Sc to Zn
due to increase in nuclear charge.
d. Physical constant: Physical constant like melting point and boiling point of
these elements are very high (except Zn) due to small atomic radii of these
elements.
e. Ionization potential: The Ionization Potential values of transition elements
are intermediate between the s-block and p-block elements. Due to intermediate
values they form ionic compounds as well as covalent compounds.
f. Colour: Except zinc all the transition metals complex ions are colourless due
to presence of unpaired electrons.
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2) Why are complexes of the d-block elements coloured?
The complexes of d-block elements are coloured due to the following reasons:
a. Electronic transitions of d-electrons within the d sub-shell. These are known
as d->d transitions. D0 and d10 metal ions do not show
these transitions.
b. Electronic transitions from the metal ion to the ligand (M->L transitions)
or ligand to the metal ion (L->M transitions), which are known as
charge-transfer transitions, and these can occur for d0 to d10
metal ions.
c. Sometimes the ligands themselves are coloured and thus the complexes are also
coloured.
3) What are transition metals? Why are Scandium and Zinc not counted as
transition metals even though they belong to the d-block?
A transition metal is one which has incompletely filled d orbitals but
exceptions are always there. As see here in the case of Scandium and Zinc.
Scandium has the electronic configuration as [Ar] 3d14s2.
While forming an ion it loses its outer 3 electrons and thus ends up with the
structure of Argon. Hence it does not fit with the definition of Transition
metals.
Zinc has the electronic configuration as [Ar] 3d104s2.
While forming an ion it loses the two 4s electrons and thus ends up with the
electronic structure as [Ar]3d10. Therefore Zinc has full d orbitals
and deviates from the definition of the transition metals.
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