D-Block Elements
The elements in the groups from 3 to 12 or The elements in the groups IB, IIB, IIIB, IVB, VB, VIB, VIIB and, VIIIB of the periodic table are called as d-block elements. The 4th, 5th, 6th and 7th period consists of 10 elements each and are called as d-block elements. Thus, In all there are 40 d-block elements. The d-block elements have partially filled d-orbitals. They are placed in between the s-block and p-block elements in the periodic table. They are also called as Transition elements. The name " Transition " originates from their place between s and p-block elements in the periodic table. The d-block elements are all metals with their last two shells incompletely filled.
Characteristic Properties of elements in d-block of Modern Periodic Table :-
The properties of d-block elements are intermediate between s-block and p-block elements.
1) Electronic Configuration :- The general electronic configuration of d-block elements is ns 2 ( n - 1 ) d1 to 10 . But in the elements of the 12th group i.e Zn, Cd and Hg ,the incoming electron occupy the ns shell instead of ( n - 1 ) d subshell which are already saturated and they should therefore, be excluded from d-block elements , But, since they posses properties similar to those of d-block elements, for all practical purposes they are placed with d-block elements.
The d-block elements are classified into 4 series:-
a) 3d series containing 10 elements
:-
They have incomplete 3d-orbital.
Elements starting from Sc (21) to Zn (30) are present in these series.
b) 4d series containing 10 elements
:-
They have incomplete 4d-orbital.
Elements starting from Y (39) to Cd(48) are present in these series.
c) 5d series containing 10 elements
:-
They have incomplete 5d-orbital.
Elements starting from La (57) to Hf (72) to Hg (80) are present in these
series.
d) 6d series containing 10 elements
:-
They have incomplete 6d-orbital. This
is the incomplete series.
2) Metallic Character :- All the d-block
elements have 1 or 2 electrons in their outermost shell and thus all are
metals. All are hard,ductile and malleable solids with strong bonding due to
their greater effective nuclear charge and large number of valence electrons
(except Hg which is liquid) .
3) Atomic and Ionic Radii :- The Atomic and
Ionic Radii of transition elements are smaller than their corresponding s-block
elements and are greater than their corresponding p-block elements. The Atomic
and Ionic Radii of transition elements for a given series show a decreasing
trend for first 5 elements and then becomes almost constant for next 5 elements
of the series. For eg :- In 3d series atomic radius decreases from Sc(21) to
Mn(25) and then becomes constant for next five, i.e. Fe(26) to Zn(30). This is
due to the combined effect of increasing effective nuclear charge and
increasing screening effect along the period.
4) Atomic volume and density :- The size decreases
along the period and therefore atomic volume also decreases along the period.
Atomic volumes are smaller than group 1 and 2 members, i.e. s-block elements.
The density,however,increases along the period.
5) Boiling and Melting points :- All the transition
elements have high M.P. and B.P. , as compared to s-block elements due to their
strong metallic bonding and unpaired d-electrons. M.P. of transition elements
of a given series increases on moving from left to right in a period and
attains a maximum value and after that M.P. goes on decreasing towards the end
of period. These higher values are due to small atomic radii of transition
elements which provides greater inter atomic forces of attraction. However Zn,
Cd, Hg have relatively low values of M.P. and B.P. Due to their completely
filled d-orbitals
.
6) Ionisation Energy :- The Ionisation
energy of d-block elements lies in between the of s-block and p-block elements.
Thus they are more electropositive than p-block elements and less
electropositive than s-block elements. Since smaller being atomic size, thus
high Ionisation Energy is noticed for transition elements. Ionization Energy
values first increases upto Mn(25) and then becomes irregular or constant due
to irregular trend of atomic size after Mn(25) in 3d series,also similar trend
is noticed in 5d and 6d series. However Zn, Cd, Hg have abnormally high values
of Ionization Energy on account of greater stability
of s-subshell.
7) Oxidation state :- The Transition
elements show variable oxidation state in their compounds. Reason for this
variable oxidation state is that there is a very small energy difference in between
(n-1)d and ns orbitals. As a result ,electrons of (n-1)d orbitals as well as
ns-orbitals take part in bond formation. Variation in oxidation state is
related to their electronic configuration. For eg :-
Ti : +2, +3, +4.
Cr : +1, +2, +3, +4, +5, +6.
Mn : +2, +3, +4, +6, +7.
Fe : +2, +3.
Cu : +1, +2.
8) Standard Electrode Potential and
Reducing properties :- Expect Cu and Hg, the standard reduction potential
of d-block elements in acid solution is generally negative, but however Cu and
Hg are having positive electrode potential. The d-block elements are not good
reducing agents in comparision to s-block elements due to their high heats of
sublimation , high ionisation potential and low heats of hydration of their
ions.
9) General Chemical Reactivity :- The d-block
elements have been unreactive in comparision to s-block elements due to their
high ionisation energy, high heats of sublimation and low heats of hydration.
But however Transition metals vary
widely in their chemical reactivity. Many of them are sufficiently
electropositive to dissolve in mineral acids, although a few are 'noble' ,that
is, they areunaffected by simple acids. The metals of the first series with the
exception of copper are relatively more reactive and can be oxidised.
Transition metals form alloys among
themselves. The alloys of transition metals are hard and have high melting
point as compared to other metal.
10) Conductivity :- All the Transition
elements are good conductors of heat and electricity.
11) Colour :- Except zinc all
the transition metals complex ions are colourless due to presence of unpaired
electrons.
The colours exhibited by some
transition metal ions are :-
1. Cu2+ (Blue).
2. Fe2+ (Green).
3. Ti3+ (Purple).
4. Mn3+ (Violet).
5. Fe3+ (Yellow).
12) Flame colouration :-The d-block
elements impart no characteristic colour to the flame. We know that when an
electron gains energy, it gets excited to a higher energy level, and when it
looses that energy, it again comes back to the same level, by giving out some
amount of radiation. This released energy appears in the form of colour. The
d-block elements do not impart colour to the flame as their electron don't jump
to the higher energy level when brought in the flame.
Thank you for visiting the
blog....!!!!!
very good
ReplyDeleteThank You Mr.Aneesh Rockz .
ReplyDeleteChemAvishkar
can you like list all of the elements
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