Transcript Chapter 20 The Transition Metals

Chapter 19. The Transition Metals
19.1 Overview of the Transition
Metals
19.2 Coordination Complexes
19.3 Bonding in Coordination
Complexes
19.4 Metallurgy
19.5 Applications of Transition
Metals
19.6 Transition Metals in Biology
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19.1 Overview of the Transition Metals
Learning objective:
Predict periodic properties of transition metals
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19.1 Overview of the Transition Metals
 Remember that the nd orbital always is more stable than the
(n+1)s orbital
 Transition metal cations usually have empty (n+1)s orbitals.
 Inner Transition Metals – lanthanides and actinides
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Physical Properties
 Conduct heat and electricity
 Are malleable and ductile.
 Most have shiny gray appearance – “silvery”
 Some exceptions: copper (orange), gold (yellow)
 Melting points and densities show periodic trend.
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Melting Points
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Densities
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Oxidation States
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Representative Transition Metal Compounds
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19.2 Coordination Complexes
Learning objective:
Recognize and name transition metal coordination
complexes
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19.2 Coordination Complexes
 Ligand – a species that has lone pairs of electrons
available to donate to a metal atom or cation. (H2O,
NH3, CO, etc..)
 Dissolved transition metals usually complex with water
molecules.
 Usually, the colour associated with the solution comes
from the complex formed in water.
 Replacing water with another ligand (for instance
ammonia) usually results in a colour change.
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Complexes of Ni2+
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Colour Changes Indicate Complexation
Ni(II) Sulphate
NH3 (aq)
Solvent Evaporation
[Ni(NH3)6]SO4
[Ni(H2O)6]2+
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Nature of Ligands
 The metal ligand bond is formed by the overlap of an
empty valence orbital on the metal with the lone pair
orbital on the ligand.
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Common Ligands
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Common Ligands
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Structures of Coordination Complexes
Complexes with
coordination
number 2 are linear
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Structures of Coordination Complexes
Four coordinate complexes are either square planar or
tetrahedral
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Structures of Coordination Complexes
Six coordinate
(octahedral) is
the most
prevalent
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Isomers
 Isomers –
chemical
compounds with
the same
formula but
different
structures.
 Isomers can have
different
chemical and
physical
properties.
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Linkage Isomers
Linkage
isomers
occur
when a
ligand can
bond to a
metal
using
either of
two donor
atoms.
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Example 19 – 1 Isomers of
Coordination Compounds
Draw ball-and-stick models of all possible isomers of the
octahedral compound [Cr(NH3)3Cl3].
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Naming Coordination Compounds
1.
2.
3.
4.
5.
6.
As with all salts, name the cation before the anion.
Within the complex, first name the ligands in alphabetical order, and
then name the metal.
If the ligand is an anion, add the suffix – o to the stem name (bromo,
Br-). The simplest neutral ligands have special names: aqua (H2O),
ammine (NH3), and carbonyl (CO). Other neutral ligands retain their
usual names (see Table 19 – 3)
Use a Greek prefix (di-, tri-, etc.) to indicate the number of identical
ligands. If the name of the ligand already incorporates one of these
prefixes, enclose the ligand name in parentheses and use the
alternative prefixes bis- (two), tris- (three), and tetrakis- (four).
Ignore these numerical prefixes in determining the alphabetical
order of the ligands.
If the coordination complex is an anion, add the suffix –ate to the
stem name of the metal.
After the name of the metal, give the oxidation number of the metal
in parentheses.
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Latin Names of Metals in Anionic Complexes
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Example 19 – 2 Naming
Coordination Compounds
What is the IUPAC name for each of the following
coordination compounds?
(a) [Ni(H2O)6]SO4; (b) [Cr(en)2Cl2]Cl; and (c) K2[CoCl4]
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Example 19 - 3
Determine the formulas of the following coordination
compounds:
a. fac – Triamminetriiodoruthenium (II)
b. cis – Chlorohydridobis(trimethylphosphine)platinum(II)
c. Sodium hexacyanoferrate(II)
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19.3 Bonding in Coordination Complexes
Learning objective:
Use crystal field theory to explain the colour and
magnetic properties of complexes
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19.3 Bonding in Coordination Complexes
 Crystal field theory – focuses on electrical interactions
between a transition metal ion and its ligands.
 Most accurately explains colour and magnetic
properties.
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Crystal Field Splitting Energy
 Not all of the orbitals
are at the same energy.
 The difference in energy
between the orbitals is
the crystal field splitting
energy, D.
 The lower energy
orbitals are called t2g
and the higher energy
orbitals are called eg
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Populating the d Orbitals
 Must follow Pauli and Hund’s Rule.
 So the first three electrons will go in
the first three lower energy orbitals.
But, where does the next electron go?
 Placing it with another electron
destabilizes the system, but putting it
in the higher energy orbital increases
the energy of the system (Pairing
Energy)
 If the electron is placed in the 4th dorbital, it is termed high-spin.
 If the electron is paired with another
electron, it is termed low-spin.
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Example 19 – 4 Electron Configurations
Draw an energy level diagram and write the d electron
configuration of [Pt(en)3]Cl2.
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Magnetic Properties of
Coordination Complexes
 So which energy level is the 4th electron in? The
magnetic properties of the complex will depend on
this.
 The amount of paramagnetism in a molecule
depends on the number of unpaired electrons.
 This can be measured with a Magnetic Susceptibility
Balance.
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Magnetic Susceptibility Balance
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Example 19 – 5 High- and Low-Spin Complexes
[Fe(NH3)6]2+ is paramagnetic but [Co(NH3)6]3+ is not.
Write the electron configuration for each of these
metal complexes and draw energy level diagrams
showing which has the higher D.
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Contributions to Crystal Field Splitting Energy
 Ligands play an important factor in the value of D.
 The energetic effects of ligands are explained by the
spectrochemical series.
 D is also affected by the oxidation state and the
position of the metal in the periodic table.
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Example 19 – 6 Crystal Field Splitting Energy
Arrange the following complexes in order of increasing
crystal field splitting:
[Fe(H2O)6]2+, [Fe(H2O)6]3+, [FeCl6]4-, [Ru(H2O)6]3+
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Colour in Coordination Complexes
 Colour depends on the splitting energy.
 When a coordination complex absorbs light, the crystal
field splitting energy must match the energy of the
absorbed light.
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Relationships Among Wavelength, Colour, and
Crystal Field Splitting Energy
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Cr3+ Coordination Complexes
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Example 19 – 7 Determining the Value of D
Titanium (III) chloride dissolves in water to give [Ti(H2O)6]3+. This
complex ion has the absorption spectrum shown. From the
wavelength at which maximum absorption occurs, predict the
colour of the solution and calculate D in kilojoules per mole.
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Square Planar Complexes
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Tetrahedral Complexes
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19.4 Transition Metals In Biology
Learning objective:
Explain the importance of transition metal complexes in
biological processes
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19.4 Transition Metals In Biology
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Metalloproteins
Large macromolecules of amino acids that play three
essentials roles:
1. Transport and store molecules

Depend on the ability of transition metals to bind and
release ligands
Enzymes – catalysts for biochemical reactions, also
based on the bind/release mechanism.
3. To serve as redox reagents – ideal due to ability to
shuttle between two or more oxidation states.
2.
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Haemoglobin
Deoxyhaemoglobin
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Haemoglobin
Myoglobin
Also an O2 Transport protein
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Ferritin
Iron Transport Protein
Contains 24
nearly identical polypeptides
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Redox
Proteins
Cytochrome c
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Plastocyanin
19.5 Metallurgy
Learning objective:
Explain the chemistry of essential steps in the
production of pure metals from ores
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19.5
Metallurgy
Metallurgy – the
production and
purification of
metals from
naturally
occurring ore
deposits.
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Overview of Metallurgical Processes
Once ore is obtained, contaminants
must be removed:
 Flotation – a common physical
separation process in which ore is
crushed and mixed with water to
form a thick slurry.
 The slurry is mixed with oil and a
surfactant.
 The polar heads of the surfactant
coat the mineral particles, but the
nonpolar tails make the particles
hydrophobic.
 The minerals become trapped in a
froth, which is removed from the
top.
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Leaching
 A separation technique which uses solubility properties
to separate the components of ores.
 Sulphide ores may require roasting (high heat
oxidation) before leaching can occur. The roasting
process converts the sulphide ores to metal oxides.
 Because roasting produces SO2 (a environmental
toxin), an aqueous process has been developed.
Though the aqueous acidification is more costly, it is
preferred over the pollution produced in roasting.
 Further refining may be needed to remove more
impurities.
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Metallurgy of Transition Metals
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Iron and Steel
 Iron – the dominant
structural material of
modern times.
 Steel – iron
strengthened by
additives (700 million
tons/year).
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Iron and Steel
Reduction of iron oxides in the blast furnace:
3 Fe2O3 (s) + CO (g) → Fe3O4 (s) + CO2 (g)
Fe3O4 (s) + CO (g) → 3 FeO (s) + CO2 (g)
FeO (s) + CO (g) → Fe (l) + CO2 (g)
Removal of silica:
CaCO3 (s) → CaO (s) + CO2 (g)
CaO (s) + SiO2 (s) → CaSiO3 (l)
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“Slag”
Titanium
Purified by first reacting with Cl2 gas to form TiCl4 and
then reacting it with molten magnesium to yield Ti in a
replacement reaction:
TiO2 (s) + C (s) + 2 Cl2 (g) → TiCl4 (g) + CO2 (g)
TiCl4 (g) + 2 Mg (l) → Ti (s) + 2 MgCl2 (l)
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Copper
Most copper ore is less than 1% Cu, so it requires
expensive refining including flotation, roasting and
electrolysis:
1. Concentrated ore is roasted to yield FeCuS2 (s).
2. 2 FeCuS2 (s) + 3 O2 (g) → 2 CuS (s) + 2 FeO (s) + 2 SO2 (g)
3. CuS (s) → Cu2S (s)
SO2 (g)
4. 2 Cu2S (l) + 3 O2 (g) → 2 Cu2O (l) + 2 SO2 (g)
waste!
2 Cu2O (l) + Cu2S (l) → 6 Cu (l) + SO2 (g)
Impure copper, must
be further refined
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Electrolytic Copper Production
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Metal Mining in Canada
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19.6 Applications of Transition Metals
Learning objective:
Recognize the importance of transition metals in
everyday life
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19.6 Applications of Transition Metals
 Titanium – 9th most abundant element
 High strength, low density
 When alloyed with Al or Sn, has
the highest strength-to-weight ratio
of all engineered materials.
 Major use in construction of
aircraft frames and jet engines.
 Also resistant to corrosion, thus used in pipes and pumps.
 TiO2 – most important compound of Ti, chemically inert and
nontoxic, used in cosmetics and toothpaste.
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Chromium
 0.012% of the Earth’s Crust
 Derived from the Greek word chroma
meaning color - forms a wide variety of
compounds with beautiful colors
 Main use: metal alloys such as stainless
steel (20% Cr)
 Cr (VI) is highly toxic.
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Copper, Silver and Gold
 First three pure metals known to humanity.
 Cu – produced for electrical wiring and plumbing, also
alloys to form bronze and brass, resists oxidation, toxic
in large amounts.
• Ag – produced as by-product of
other metal purifications, used in
sterling silver (alloy with Cu),
jewelry, batteries, and
photography.
• Au – used in the manufacture of
jewelry, effective in the treatment
of rheumatoid arthritis, may have
anticancer properties.
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Zn and Hg
 Found as sulphide ores.
 Zn – used to protect iron from corrosion, also part of
the brass and bronze alloys, ZnO used as catalyst in the
production of rubber and also as a common sunscreen.
 Hg – used to extract Ag and Au from their ores, used in
fluorescent lights, thermometers, barometers,
electrical switches and electrodes.
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The Platinum Metals
 Ru, Os, Rh, Ir, Pd and Pt
 Found mingled together in ore deposits
 Most commonly used as catalysts
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Chapter 19 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 19 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 19 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 19 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 19 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 19 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.