20.1 The Transition Metals: A Survey

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Vanadium metal (center) and in solution as
V2(aq), V3(aq), VO2(aq), and VO2(aq), (left
to right).
Chapter 20. Transition Metals and Coordination
Chemistry

• 20.1 The Transition Metals A Survey
• 20.2 The First-Row Transition Metals
• 20.3 Coordination Compounds
• 20.4 Isomerism
• 20.5 Bonding in Complex Ions
• The Localized Electron Model
• 20.6 The Crystal Field Model
• 20.7 The Molecular Orbital Model
• 20.8 The Biological Importance of
• Coordination Complexes

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Figure 18.1 The periodic table.
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Figure 12.39 Special names for groups in the
periodic table
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Figure 12.39 Special names for groups in the
periodic table (contd)
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Figure 20.1 Transition elements on the periodic
table
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Figure 12.28 The orbitals filled for elements
in various parts
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Some Transition Metals Important to the U.S.
Economy and Defense
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20.1 A Survey of the Transition Metals

• Recall the Representative Elements, Groups 1A
  8A
• Chemical similarities occur within the vertical
  groups

• Large changes in chemistry across a given
  period as the number of valence electrons changes
• E.g. Na Mg Al Si P S Cl Ar

• increasing metallic character
• decreasing ionization energy

• Transition Metals
• Similarities within a given period as well as
  within a given vertical group.
• this huge contrast with the representative
  elements is due to the fact that the last
  electrons added to the transition metal elements
  are inner electrons
• d electrons in d block transition metals
• f electrons in the lanthanides and actinides

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• the inner d and f electrons cannot participate in
  bonding as readily as the s and p electrons.
• Characteristics of the transition metals
• typical metals
• metallic luster
• high electrical and thermal conductivities
• Differences in Physical Properties among the
  transition metals can be large
• E.g. W, tungsten (mp 3400?) vs Hg,
  mercury (mp lt 25?)
• hard and high strength vs soft
• Fe, iron and Ti Cu, Au, Ag
• ready rxn w/ O2 to form oxides vs no rxn with
  O2
• Cr, Ni, Co, Al, Fe Au,
  Ag, Pt, Pd
• Ionic compounds with nonmetals
• Often more than one oxidation state
• E.g. FeCl2 FeCl3
• 2 3
• the cations are often complex ions, species in
  which the transition metal ion is surrounded by a
  number of ligands.

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Molecular model The CO(NH3)63 ion
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• Ligands are molecules or ions that behave
• as Lewis bases, i.e. have a lone pair of
  electrons.
• Most compounds of the transition metals are
  colored.
• the transition metal ion can absorb visible
  light.
• Many transition metal compounds are
  paramagnetic.
• because they contain unpaired electrons
• Electron Configurations (See Section 12.13)
• The 3d orbitals begin to fill after the 4s
  orbital is complete.
• e.g. Sc Ar4s23d1
• Ti 4s23d2
• Y 4s23d3
• Cr 4s13d5
• Mn 4s23d5
• Cu 4s13d10
• Zn 4s23d10
• for most elements of the first-row transition
  metals 4s23dn has a lower energy than 4s13dn1
  except chromium and copper.
• The 4s and 3d orbital energies are very similar.

Co2, Mn2, Cr3, Fe3, Ni2
(See Table 20.2)
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Table 20.2 Selected Properties of the First-Row
Transition Metals
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• Electron configurations of ions of the first-row
  transition metals
• the energy of the 3d orbitals is significantly
  less than that of the 4s orbital.
• E.g. Sc 4s23d1 Sc2 3d1
• Ti 4s23d2 Ti3 3d1
• Zn 4s23d10 Zn2 3d10
• these ions do not have 4s electrons (since the
  3d orbitals are lower in energy)
• Oxidation States and Ionization Energies
• Various ions formed by losing electrons
• E.g. Ti ? Ti2, Ti3, Ti4
• 4s23d2 most
  common
• (See Table 20.2)
• to the right of the row the higher oxidation
  states are not observed because the 3d orbitals
  become lower in energy as the nuclear charge
  increases, making electrons difficult to remove.
• e.g. Zn ? Zn2 Zn3,
  Zn6, Zn10, etc ? NOT OBSERVED
• 4s23d10 observed
• (See Figure 20.2)

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Figure 20.2 plots of the first (red dots) and
third (blue dots) ionization energies for the
first-row transition metals
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• Standard Reduction Potentials
• The potential of the half-reaction
• M(s) ? Mn ne-
• characterizes the reducing ability of the metal.

• this is the reverse of usually tabulated
  half-reactions and the potentials are opposite in
  sign to tabulated values in Table 20.2.

• Since by definition ?o 0 for
• 2H 2e- ? H2
• all the first-row transition metals, except
  copper, can reduce H ions to hydrogen gas in 1M
  aqueous solutions of strong acids
• M(s) 2H(aq) ? H2 (g) M2(aq)

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• The 4d and 5d Transition Series
• Comparison of the atomic radii of 3d, 4d, and 5d
  elements
• See Figure 20.3
• general decrease in size in going from left to
  right across each series
• significant increase in size from 3d to 4d
• 4d and 5d metals are very similar in size
• this is due to the lanthanide contraction.
• lanthanide series elements between lanthanum
  (La) and hafnium (Hf)
• ?
• filling of 4f orbitals which are in the interior
  of the atoms do not affect size of the 5d
  elements
• 4d and 5d transition metals, though not as
  common as 3d metals, have some very useful
  properties.
• E.g. The platinum group metals Ru, Os, Rh,
  Ir, Pd and Pt are widely used as catalysts in
  many industrial processes.

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Figure 12.28 The orbitals filled for elements
in various parts
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Figure 12.31 The positions of the elements
considered in Example 12.8
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Figure 20.3 Atomic radii of the 3d, 4d, and 5d
transition series.
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Figure 20.1 Transition elements on the periodic
table
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20.2 The First-Row Transition Metals

• Highlights of some properties or chemistry of the
  10 3d transition metals.
• Scandium, Sc
• 3 oxidation state in compounds, e.g. ScCl3,
  Sc2O3, etc
• most of its compounds are colorless and
  diamagnetic.
• Titanium, Ti
• fairly abundant (0.6 by mass of the earths
  crust)
• low density high strength high mp (1,672?)

excellent structural material jet engines,
Boeing 747 jetliners, etc.

• titanium (?) oxide (or titanium dioxide), TiO2
  is the most common compound.
• -- white pigment used in many products paper,
• paint, linoleum, plastics, cosmetics, etc.

3. Vanadium, V The most common oxidation state
is 5 as in V2O5 (orange, mp 650 ?) and VF5.
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Figure 20.4 Titanium bicycle
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• Chromium, Cr
• Main ore is chromite (FeCr2O4)
• FeCr2O4 (s) 4 C (s) ? 4 CO (g) Fe (s) 2Cr
  (s)

• common oxidation states in compounds 2, 3,
  and 6
• Cr2 (chromous ion)
• Cr3 (chromic ion)
• chromium (IV) oxide conc. sulfuric acid

• 5. Manganese, Mn
• The only member of the 3d metals that can exist
  in all oxidation states from 2 to 7.
• Manganese (VII) ion MnO4-
• permanganate ion
• ( a strong oxidizing agent in solution)

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Manganese nodules on the sea floor
Source Visuals Unlimited
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• Iron, Fe
• Quite abundant (4.7 of the earths crust)
• Its chemistry mainly involve its 2 and 3
  oxidation states.

• 7. Cobalt, Co
• mainly 2 and 3 states
• compounds with 0, 1 and 4 states are also known

• 8. Nickel, Ni
• mainly in the 2 oxidation state.
• aqueous solutions of nickel (II) salts contain
  Ni(H2O)62 ion,
• characteristic emerald green color

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Aqueous solution containing the Ni2 ion
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• 9. Copper, Cu
• widely available in ores (sulfides,
• chlorides, carbonates etc.)
• used in electrical applications (wires, cables,
  etc)
• also used in water pipes in homes
• many common alloys contain copper
• e.g. brass, bronze, sterling silver, 18- and 14-
  Karat gold
• chemistry involves 2 oxidation state,
• but also some compounds with the 1 oxidation
  state.

• 10. Zinc, Zn
• 2 oxidation state only
• used mainly for producing galvanized steel.
• Zinc (II) salts are colorless.

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20.3 Coordination Compounds

• A coordination compound consists of a complex ion
  and counter ions.
• it is an ionic compound, electrically neutral.
• complex ion transition metal ion attached
  ligands.
• E.g. Co(NH3)5ClCl2
• Co(NH3)5Cl2 ? complex ion
• 2 Cl- ? counter ions (anions)
• coordination compounds ionize in solutions
  (similar to simple salts)
• Co(NH3)5ClCl2 (s)
  Co(NH3)5Cl2(aq) 2 Cl- (aq)
• Coordination Number of Metal Ions
• The number of bonds formed between a metal ion
  and the ligands in the complex ion is termed the
  coordination number.
• depending on the size, charge, and electron
  configuration of the transition metal ion, the
  coordination number can be from 2 to 8.

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• many metal ions show more than one coordination
  number.
• for the typical geometries for the various
  typical coordination numbers see Figure 20.6.
• Ligands
• a neutral molecule or ion having a lone pair that
  can be used to form a bond with a metal ion.
• Lewis bases by definition are ligands
• the metal ion is a Lewis acid
• a metal ligand bond is called a coordinative
  covalent bond.
• it results from a Lewis acid base interaction
  in which a ligand donates an electron pair to an
  empty orbital on a metal ion.

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Figure 20.6 Ligand arrangements for
coordination numbers 2, 4, and 6