D block F block class 12 notes
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Introduction based on NCERT textbook:
The d-block of the periodic table contains the elements
of the groups 3-12 in which the d orbitals are
progressively filled in each of the four long periods.
The elements constituting the f -block are those in
which the 4 f and 5 f orbitals are progressively filled
in the latter two long periods; these elements are formal
members of group 3 from which they have been taken
out to form a separate f-block of the periodic table.
The names transition metals and inner transition
metals are often used to refer to the elements of d-and
f-blocks respectively.
There are mainly three series of transition
metals, 3d series (Sc to Zn), 4d series (Y to Cd) and 5d
series (La to Hg, omitting Ce to Lu). The fourth 6d
series which begins with Ac is still incomplete. The two
series of the inner transition metals, (4f and 5f) are
known as lanthanoids and actinoids respectively.
Strictly speaking, 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. Zinc,
cadmium and mercury of group 12 have full d
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configuration in their ground state as well as in their
common oxidation states and hence, are not regarded
as transition metals. However, being the end members
of the three transition series, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms set the study of the transition elements and their compounds apart from that of the main group
elements. However, the usual theory of valence as
applicable to the main group elements can also be
applied successfully to the transition elements.
Various precious metals such as silver, gold and
platinum and industrially important metals like iron,
copper and titanium form part of the transition metals.
In this Unit, besides the introduction, we shall first deal
with the electronic configuration, occurrence, and general
characteristics of the transition elements with special
emphasis on the trends in the properties of the first
row (3d) transition metals and the preparation and
properties of some important compounds. This will be
followed by consideration of certain general aspects such
as electronic configurations, oxidation states, and the chemical reactivity of the inner transition metals.
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