Transcript 17.The d-Block Elements.General properties

Lecture 17. The d-Block Elements.
General properties
PhD. Halina Falfushynska
Why Study Descriptive Chemistry of Transition
Metals
• Transition metals are found in nature
– Rocks and minerals contain transition metals
– The color of many gemstones is due to the presence of
transition metal ions
• Rubies are red due to Cr
• Sapphires are blue due to presence of Fe and Ti
– Many biomolecules contain transition metals that
are involved in the functions of these biomolecules
• Vitamin B12 contains Co
• Hemoglobin, myoglobin, and cytochrome C contain Fe
Why Study Descriptive Chemistry of Transition
Metals
• Transition metals and their compounds have many
useful applications
– Fe is used to make steel and stainless steel
– Ti is used to make lightweight alloys
– Transition metal compounds are used as pigments
• TiO2 = white
• PbCrO4 = yellow
• Fe4[Fe(CN)6]3 (prussian blue)= blue
– Transition metal compounds are used in many industrial
processes
Myoglobin, a protein that stores O2 in cells
Coordination Environment of Fe2+ in
Oxymyoglobin and Oxyhemoglobin
Ferrichrome (Involved in Fe transport in bacteria)
Periodic Table
d block transition elements
f block transition elements
d-Block Transition Elements
IIIB
IVB
VB
Sc
Ti
V
Y
La
VIIIB
VIB VIIB
IB
IIB
Cr
Mn
Fe
Co
Ni
Cu
Zn
Zr
Nb Mo
Tc
Ru
Rh
Pd Ag
Cd
Hf
Ta
Re
Os
Ir
Pt
Hg
W
Au
Most have partially occupied d subshells in
common oxidation states
Energy
4p
3d
4s
3p
3s
2p
2s
1s
Sc
1s2 2s2 2p6 3s2 3p6 3d1 4s2
Electronic Configurations
Element
Sc
Ti
V
Cr
Mn
Configuration
[Ar]3d14s2
[Ar]3d24s2
[Ar]3d34s2
[Ar]3d54s1
[Ar]3d54s2
[Ar] = 1s22s22p63s23p6
Electronic Configurations
Element
Fe
Co
Ni
Cu
Zn
Configuration
[Ar] 3d64s2
[Ar] 3d74s2
[Ar] 3d84s2
[Ar]3d104s1
[Ar]3d104s2
[Ar] = 1s22s22p63s23p6
General Properties of the d-Block
Elements and Their Trends
• Metallic character: All transition elements are
•
metallic in nature, i.e. they have strong metallic bonds.
This is because of presence of unpaired electrons. This
gives rise to properties like high density, high
enthalpies of atomization, and high melting and boiling
points.
Lanthanoid Contraction: The steady decrease in
the atomic and ionic radii of the transition metals as
the atomic number increases. This is because of filling
of 4f orbitals before the 5d orbitals. This contraction is
size is quite regular. This is called lanthanoid
contraction.
General Properties of the d-Block
Elements and Their Trends
• Ionisation enthalpy: There is slight and irregular variation
in ionization energies of transition metals due to irregular
variation of atomic size. The I.E. of 5d transition series is higher
than 3d and 4d transition series because of Lanthanoid
Contraction.
• Oxidation state: Transition metals show variable
oxidation states due to tendency of (n-1)d as well as ns
electrons to take part in bond formation.
• Magnetic properties: Most of transition metals are
paramagnetic in nature due to presence of unpaired electrons.
It increase s from Sc to Cr and then decreases because number
of unpaired and then decrease because number of unpaired
electrons increases from Sc to Cr and then decreases.
General Properties of the d-Block
Elements and Their Trends
• Catalytic properties: Most of transition metals
are used as catalyst because of (i) presence of
incomplete or empty d – orbitals, (ii) large surface
area, (iii) varuable oxidation state, (iv) ability to
form complexes, e.g., Fe, Ni, V2O3, Pt, Mo, Co and
used as catalyst.
• Formation of coloured compounds: They form
coloured ions due to presence of incompletely
filled d – orbitals and unpaired electrons, they can
undergo d – d transition by absorbing colour from
visible region and radiating complementary colour.
General Properties of the d-Block
Elements and Their Trends
• Fourth-period d-block
elements form ionic bonds
with somewhat less ionic
character than do the
metals of the s-block.
• Lower oxidation states (+2,
+3) usually correspond to
ionic character.
• For Co through Zn, relative
energies of the 4s and 3d
subshells are such that few
(or no) 3d electrons are lost
in forming ions.
For Zn, the 4s–3d
energy difference is
so large that only 4s
electrons are lost.
Some Properties of the Fourth
Period d-Block
• In the fourth-period d-block, only
scandium is active enough to
displace H2 from H2O.
• These elements have moderate to
high melting points and
moderately high densities.
• Electrical and thermal
conductivities of these
elements are very high. Copper
is second only to silver in
electrical conductivity.
Atomic Radii of the
d-Block Elements
• Size does not appear to
increase significantly between
fifth and sixth period elements.
• The electrons in 4f orbitals are
not very good at screening
valence electrons from the
nucleus.
• Thus, the strength of attraction
of valence electrons to the
nucleus is greater than
expected in the sixth period.
The phenomenon is known as
the lanthanide contraction.
Characteristic properties:
Color: The complexes of the d-block metal ions are
usually colored, except, very often, those of d0 and d10
metal ions. The colors are due to:
a) electronic transitions of d-electrons within the d subshell. 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) The ligands themselves may be colored, and this color
may contribute to the color of the complex.
Characteristic properties:
Paramagnetism: When there are unpaired electrons in the d
sub-shell, these will lead to paramagnetism. Thus, in
[Cr(H2O)6]3+ the three d electrons (it is d3) are unpaired.
Thus, like the O2 molecule which is paramagnetic, Cr(III) is
paramagnetic. A d10 metal ion (e.g. Zn(II)) has a filled d
sub-shell, and a d0 metal ion (e.g. Ti(IV)) has no delectrons, so neither of these can be paramagnetic.
Variable oxidation states: Most d-block metal ions display
variable oxidation states. Thus, for example, Mn displays
oxidation states from Mn(-III) (in [Mn(CO)(NO)3]) through
Mn(0) (in [Mn2(CO)10]) to Mn(VII) (in [MnO4]-).
Oxidation states of first-row d-block ions:
The most stable oxidation states are in red, rarer oxidation states pale blue:
3
4
Sc
Ti
3
2
3
4
These achieve
the group
oxidation state
5
6
V
1
2
3
4
5
7
Cr
1
2
3
4
5
6
8
Mn
1
2
3
4
5
6
7
9
Fe
1
2
3
4
5
6
Maximum at Mn(VII)
10
Co
1
2
3
4
11
Ni
1
2
3
4
12
Cu
1
2
3
4
The higher oxidat-ion
states become
progressIvely less
stable as the divalent
state becomes
dominant
Zn
2
Oxidation States of Transition Elements
Sc
+3
Ti
V
Cr
Mn Fe
Co
Ni
Cu
+1
+1
+2
+2
+2
+2
+2
+2
+2
+2
+3
+3
+3
+3
+3
+3
+3
+3
+4
+4
+4
+4
+4
+5
+5
+5
+5
+6
+6
+6
Zn
+2
+4
+7
3/7/01
loss of ns e-s
Ch. 24
11
loss of ns and (n-1)d e-s
Electronic Configurations of Transition Metal Ions
• Electronic configuration of Fe3+
-’s removed
3+
valence
ns
e
Fe – 3e  Fe
[Ar]3d64s2
[Ar]3d5
first, then n-1 d e-’s
• Electronic configuration of Fe2+
• Fe – 2e-  Fe2+
valence ns e-’s removed
[Ar]3d64s2
[Ar]3d6
first
Characteristic properties:
Complex-formation: The d-block metal ions form a wide variety of
complexes, of generally high stability, with ligands such as EDTA or
F-, Cl-, and OH-, or ethylene diamine (en), as well as many others,
much as was the case for the main group metal cations. Many of the
d-block metal ions are powerful Lewis acids, as can be seen by
comparison with some main group element cations:
metal ion:
ionic radius (Å):
log K1(EDTA):
log K1(OH-):
8.5
Al3+ Co3+
0.54 0.55
16.4 41.4
13.5
2.6
Mg2+ Zn2+
0.74
0.74
8.8
16.5
5.0
The reason why the d-block cations are such strong Lewis acids will
become clear as the course proceeds.
Coordination geometries:
3+
NH3
H3N
NH3
H2N
Co
H3N
NH3
NH2 H
2
N
Co
H2N
NH3
NH2
3+
3-
CN
NC
CN
Fe
NC
N
H2
CN
CN
[Co(NH3)6]3+
[Co(en)3]3+
[Fe(CN)6]3-
octahedral
octahedral
octahedral
2+
H3N
NH3
NC
M
H3N
CN
M
NH3
2+
NH3
2-
NC
H3N
CN
[ M(NH3)4]2+
[M(CN)4]2-
square planar
square planar
M = Cu(II), Pd(II) M = Ni(II), Pd(II)
M
H3N
[M(NH3)4]2+
tetrahedral
M = Zn(II)
NH3
Coordination geometries:
octahedral
octahedral
[Cr(H2O)6]3+
[Cr(NH3)6]3+
octahedral
[CoF6]3-
tetrahedral
square
planar
[Ni(CN)4]2-
[Zn(CN)4]2-
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