Transition Metal Chemistry and
Coordination Compounds
Green/Damji – Chapter 3
Chang - Chapter 22
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The Transition Metals
22.1
Scandium
Titanium
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
22.2
d-block Elements
• elements in which the d-subshell of an atom
is being filled with electrons.
• have many similar chemical and physical
properties
• dense, hard, metallic
• note electron configuration for Cr and Cu
• ? Why doesn’t the IE change much within
the d-block as you move across period 4?
d-block Elements
Look at the next slide…
What patterns do you notice?
•
•
•
•
in electron configuration?
in electronegativity?
in ionization energy?
in size of radius?
22.1
Ionization Energies for the 1st Row Transition Metals
22.1
22.1
Transition Metals – IB description
• elements having a partially filled d-sublevel
in one of its common oxidation states
• share certain properties not shared with
other metals (including Sc and Zn)
▪ variety of stable oxidation states
▪ ability to form complex ions
▪ formation of colored ions
▪ catalytic activity
Oxidation States of the 1st Row Transition Metals
(most stable oxidation numbers are shown in red)
22.1
Variety of Stable Oxidation States* of the 1st Row Transition Metals
(most stable oxidation numbers are shown in red)
*Oxidation state (aka oxidation number)
is the charge an atom would have
in a molecule
if electrons were transferred completely.
In the molecule CO2, electrons are shared,
but we say the oxidation state of carbon is
4+ and of each oxygen is 2-.
22.1
Oxidation States of the 1st Row Transition Metals
Notice
• Transition metals on the left
have their maximum oxidation
state as the most stable. This
corresponds to the loss of all
of the 3d and 4s electrons.
[ 3+ for Sc 4+ for Ti ]
These high oxidation states often occur in the oxyanion
form. [ dichromate(VI) Cr2O72- manganate(VII) MnO4-]
see p. 86 in Green and Damjii
• Transition metals on the right have the 2+ oxidation state
as the most stable because the increasing nuclear charge
actually increases the pull on the 3d electrons, making
them less likely to be removed.
[ 2+ for Co 2+ for Ni ]
22.1
Ability to form complex ions
A complex ion contains a central metal cation
bonded to one or more molecules or ions.
The molecules or ions that surround the
metal in a complex ion are called ligands.
22.3
Ability to form complex ions
A ligand has at least one unshared pair
of valence electrons – and may be a
molecule or an ion
••
Cl
••
••
N
H H H
C
••
H
••
H
-
••
••
O
N
The complex ion may be positively or negatively
charged or may even be neutral if the charge of the
central metal ion and ligands cancel one another.
22.3
Some sample complex ions
from your lab
Cu(NH3)4 2+ royal blue
Zn(NH3)4 2+ colorless
Ag(NH3)2 + colorless
••
N
H H H
22.3
How do I know how to write the
formula for a complex ion?
Mn+ + xLm- = MLx(n-mx)
where M is the metal; n is the charge of the metal
L is the ligand; x is the number of ligands
small m is the charge of the ligand (which could be 0)
• Ag tends to accept 2 electron pairs
• Cu tends to accept 4 electron pairs
• Other transition metals tend to
accept 6 electron pairs
Transition metal ions
Extra credit opportunity:
Locate a helpful resource that explains what goes on in transition metal
complex ions to account for color. Explore the site and write notes – both
on content and on it helpfulness to an IB student. Submit on or before test
day.
http://www.chemguide.co.uk/inorganic/complexions/colour.html
22.3
Coordination Compounds
A coordination compound typically consists of a complex ion
and a counter ion.
••
N
O
H H H
H
H
The atom in a ligand that is bound directly to the metal atom is
the donor atom.
The number of donor atoms surrounding the central metal atom
in a complex ion is the coordination number.
Ligands with:
one donor atom
two donor atoms
three or more donor atoms
monodentate
bidentate
H2O, NH3, Clethylenediamine
polydentate
EDTA
22.3
Coordination Compounds
bidentate ligand
••
H2N
CH2
CH2
••
NH2
polydentate ligand
(EDTA)
Bidentate and polydentate ligands are called chelating agents
22.3
Structure of Coordination Compounds
Coordination number
2
Structure
Linear
4
Tetrahedral or Square planar
6
Octahedral
22.4
Structure of Coordination Compounds
Stereoisomers are compounds that are made up of the same
types and numbers of atoms bonded together in the same
sequence but with different spatial arrangements.
Geometric isomers are stereoisomers that cannot be
interconverted without breaking a chemical bond.
cis-[Pt(NH3)2Cl2]
trans-[Pt(NH3)2Cl2]
22.4
Structure of Coordination Compounds
trans
cis
cis-[Co(NH3)4Cl2]
trans-[Co(NH3)4Cl2]
Are these
additional
geometric
isomers of
[Co(NH3)4Cl2]?
22.4
Structure of Coordination Compounds
Optical isomers are nonsuperimposable mirror images.
cis-[Co(en)2Cl2]
trans-[Co(en)2Cl2]
optical isomers
not optical isomers
chiral
achiral
22.4
Structure of Coordination Compounds
Chiral molecules are optically
active.
22.4
The formation of Colored Ions
is due to the bonding in Coordination Compounds
All the d-orbitals are equal in energy
in the absence of ligands!
22.5
Bonding in Coordination Compounds
When you add ligands, the energy levels of the d-orbitals are often
impacted.
Crystal field splitting ( D) is the energy difference between two sets of d
orbitals in a metal atom when ligands are present
The splitting shown is for an octahedral complex. The splitting is different
for different shaped complexes.
Isolated
transition metal
atom
Bonded
transition metal atom
22.5
Bonding in Coordination Compounds
When white light passes through a compound of a
transition metal, a photon of energy is absorbed, and an
electron is promoted to a higher energy level. The light
that passes through the sample appears colored
because some light has been absorbed. (The transmitted
light is the complement of the absorbed light.)
Ex. Cu(II) compounds absorb red and yellow light so that
they look blue-green.
22.5
When white light passes through a compound of a
transition metal, the light that passes through the sample
appears colored because some light has been absorbed.
(The transmitted light is the complement of the absorbed
light.)
Ex. Cu(II) compounds absorb red and yellow light so that
they look blue-green.
22.5
Bonding in Coordination Compounds
Spectrochemical Series
I- < Br- < Cl- < OH- < F- < H2O < NH3 < CN- < CO
Weak field ligands
Small D
Strong field ligands
Large D
22.5
Catalytic Activity
Transition metals and their ions are good
catalysts because they…
• form complex ions with ligands (electron
pair donors) [means the ligand and metal
are close, as are the ligands to one another]
• have a wide variety of stable oxidation
states, so they can readily gain and lose
electrons
Heterogeneous Catalysis
Surface of metal or metal compound serves
as a place for the reaction to occur with a
reduced activation energy
MnO2
• Ex: 2 H2O2 (aq)  2 H2O (l) + O2 (g)
Ni
• Ex: CH2CH2 + H2 (g)  CH3CH3 (g)
ethene
ethane
Heterogeneous Catalysis
Catalytic converters in car exhaust systems
Pd/Pt
• Ex: 2 CO (g) + 2 NO (g)  2 CO2 (g) + N2 (g)
Haber Process
Fe
• Ex: ______ (g) + ______ (g)  2 ______ (g)
Contact Process
V2O5
• Ex: ______ (g) + ______ (g)  2 ______ (g)
Homogeneous Catalysis
• Catalyst is in the same phase as the reactants
• Often involves a metal ion being oxidized in one stage
(oxidation is the loss of electrons) and being reduced
(reduction is the gain of electrons) in a second stage.
Slow reaction:
2H2O2(aq) + H+(aq) + 2I- (aq)  2H2O (l) + I2 (s)
Catalyzed reaction:
2H2O2(aq) + H+(aq) + 2Fe2+(aq)  2H2O (l) + 2Fe3+(aq)
followed by….
2I- (aq) + 2Fe3+(aq)  I2 (s) + 2Fe 2+ aq)
(