Transcript Transition Metals

Chapter 21
Transition Metals and
Coordination Chemistry
. . . show great similarities within a given
period as well as within a given vertical group.
Key reason: last electrons added are inner
electrons (d’s, f’s). Inner d and f electrons
cannot participate as easily in bonding as can
the valence s and p electrons.
Figure 21.1 The Position of the Transition Elements on the Periodic Table
Complex Ions
. . . species where the transition metal ion is
surrounded by a certain number of ligands
(Lewis bases).
Co(NH3)63+
Pt(NH3)3Br+
Most compounds are colored, because the
transition metal ion in the complex ion can
absorb visible light of specific wavelengths.
Many compounds are paramagnetic.
Electron Configurations
• For the first row transition metals 3d orbitals begin
to fill after the 4s orbital is complete.
Sc:[Ar]4s23d1, Ti: [Ar]4s23d2, V: [Ar]4s23d3, Cr:
[Ar]4s23d4 (expected), [Ar]4s13d5 (actual).
• Chromium configuration occurs because the
energies of the 3d and 4s orbital are very similar for
the first row transition elements.
Cu: [Ar]4s23d9 (expected) but the actual is
[Ar]4s13d10.
• The energy of the 3d orbitals in transition metal
ions is significantly less that of the 4s orbital.
Oxidation States and
Ionization Energies
• The transition metals can form a variety of ions
by losing one or more electrons.
• For the first five metals the maximum possible
oxidation state corresponds to the loss of all the
4s and 3d electrons.
• Toward the right end of the period, maximum
oxidation state are not observed, in fact 2+ ions
are the most common because the 3d orbitals
become lower in energy as the nuclear charge
increases,
and the
electrons
become
increasingly difficult to remove.
Figure 21.2 Plots of the First (Red Dots) and Third (Blue
Dots) Ionization Energies for the First-Row Transition Metals
The 4d and 5d Transition Series
• There is a decrease in size going from left to
right for each of the series. There is an
increase in radius in going from the 3d to the
4d metals but 4d and 5d metals are
remarkably similar in size. This phenomenon
is the result of lanthanide contraction.
• In the lanthanide series electrons are filling
the 4f orbitals. The 4f orbitals are buried in
the interior of these atoms, the increasing
nuclear charge causes the radii of the
lanthanide elements to decrease significantly
going from left to right.
Figure 21.3 Atomic Radii of the 3d, 4d , and 5d Transition Series
A Coordination Compound
. . . typically consists of a complex ion (transition metal
ion with its attached ligand) and counter ions (anions or
cations as needed to produce a neutral compound).
[Co(NH3)5Cl]Cl2
[Fe(en)2(NO2)2]2SO4
Secondary valence: refers to the ability of a metal ion to
bind to Lewis base (ligand) to form complex ions. This
is known as coordination number (# of bonds formed
between the metal ion and the ligands)
Primary valence: refers to the ability of the metal ion to
form ionic bonds with oppositely charged ions which is
also known as oxidation state.
Figure 21.5 The Ligand Arrangements for Coordination Numbers 2, 4, and 6
A Ligand
. . . a neutral molecule or ion having a lone
electron pair (Lewis base) that can be used to
form a bond to a metal ion (Lewis acid).
Coordinate covalent bond: metal-ligand bond
formed because of the interaction of Lewis
base and Lewis acid.
Monodentate ligand: one bond to metal ion
Polydentate ligand (chelates): can form more
than two bonds to a metal ion
Naming Coordination Compounds
[Co(NH3)5Cl]Cl2
1. Cation is named before the anion. “chloride” goes last
2. Ligands are named before the metal ion. ammine,
chlorine named before cobalt
3. For ligand, an “o” is added to the root name of an
anion (fluoro, bromo). For neutral ligands the
name of the molecule is used, with exceptions.
ammine, chloro
4. The prefixes mono-, di-, tri-, etc., are used to
denote the number of simple ligands. penta
ammine
Naming Coordination Compounds
[Co(NH3)5Cl]Cl2
5.The oxidation state of the central metal ion is
designated by a (Roman numeral).
cobalt (III)
6.When more than one type of ligand is present,
they are named alphabetically.
pentaamminechloro
7.If the complex ion has a negative charge, the
suffix “ate” is added to the name of the metal.
pentaamminechlorocobalt (III) chloride
Isomerism
• When two or more species have the same
formula but different properties, they are said
to be isomers. The arrangements of the atoms
differ, and this leads to different properties.
• Structural isomerism: where the isomers
contain the same atoms but one or more bonds
differ.
• Stereoisomerism: all the bonds are the same
but the spatial arrangements of the atoms are
different.
Figure 21.8 Some Classes of Isomers
Structure Isomerism
Coordination isomerism: The composition of the
complex ion varies.
[Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4
Linkage isomerism: Same complex ion structure
but point of attachment of at least one of the
ligands differs.
[Co(NH3)4(NO2)Cl]Cl
[Co(NH3)4(ONO)Cl]Cl
Figure 21.9 Bonding of NO2-
Stereoisomerism
• Stereoisomers have the same bonds but different
spatial arrangements of the atoms.
• Geometrical isomerism (cis-trans): Atoms or
groups of atoms can assume different positions
around a rigid ring. Pt(NH3)2Cl2
• Optical isomerism: the isomers have opposite
effects on plane-polarized light.
• Dextrorotatory (d): that rotates the plane of light
to the right.
• Levorotatory (l): that rotates the plane of light to
the left.
Figure 21.10 (a) The cis isomer, (b) trans isomer
Figure 21.11 Typical cis-trans compounds of cobalt
Figure 21.12 Unpolarized Light Consists of Waves Vibrating in Many Different Planes
Figure 21.13 The Rotation of the Plane of Polarized Light by an Optically Active Substance
Figure 21.15 A Human Hand Exhibits a Nonsuperimposable Mirror Image
Figure 21.16 Isomers of I and II of Co(en)33+ are Mirror Images That Cannot Be Superimposed
Figure 21.17 The Optical Isomers of Co(en)2CI2+
The Localized Electron Model
• A complex ion with a coordination number
of 6 will have an octahedral arrangement of
ligands and complexes with two ligands
will be linear. Complex ions with a
coordination number of 4 can be either
tetrahedral or square planar.
• The interaction of a metal ion and a ligand
can be viewed as a Lewis acid-base reaction
with the ligand donating a lone pair of
electrons to an empty orbital of the metal
ion to form a coordinate covalent bond.
Figure 21.18 Hybrid Orbitals on Co3+
Figure 21.19 The Hybrid Orbitals Required for Tetrahedral, Square Planar, and Linear Complex Ions
Crystal Field Model
. . . focuses on the energies of the d orbitals.
Assumptions
1.Ligands are negative point charges.
2.Metal-ligand bonding is entirely ionic.
Strong-field (low-spin): large splitting of d orbitals
Weak-field (high-spin): small splitting of d orbitals
Spectrochemical series:
CN->NO2->en>NH3>H2O>OH->F->Cl->Br->Istrong-field
weak-field
Figure 21.20 An Octahedral Arrangement of Point-Charge Ligands and the Orientation of the 3d Orbitals
Figure 21.21 The Energies of the 3d Orbitals for a Metal Ion in an Octahedral Complex
Figure 21.23 The Visible Spectrum
Figure 21.24 Violet Light
Figure 21.26 The d Orbitals in a Tetrahedral Arrangement of Point Charges
Figure 21.27 The Crystal Field Diagrams for Octahedral and Tetrahedral Complexes
Figure 21.29 The Heme Complex
Figure 21.30 Chlorophyll
Figure 21.31 Myoglobin
Figure 21.32 Hemoglobin
Metallurgy
The process of separating a metal from its ore
and preparing it for use is known as metallurgy.
The steps in this process are:
– Mining
– Pretreatment
– Reduction to the free metal
– Purification of the metal (refining)
– Alloying
Figure 21.36 The Blast Furnace Used in the Production of Iron