Chapter 19. The Transition Metals 19.1 Overview of the Transition Metals 19.2 Coordination Complexes...

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

Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.


Learning objective:

Predict periodic properties of 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


Physical Properties

Conduct heat and electricityAre malleable and ductile.Most have shiny gray appearance – “silvery”Some exceptions: copper (orange), gold (yellow)Melting points and densities show periodic trend.


Melting Points


Densities


Oxidation States


Representative Transition Metal Compounds



Learning objective:

Recognize and name transition metal 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.


Complexes of Ni2+


Colour Changes Indicate Complexation


Ni(II) Sulphate

NH3 (aq)

[Ni(H2O)6]2+

[Ni(NH3)6]SO4

Solvent Evaporation

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.



Common Ligands

Structures of Coordination Complexes

Complexes with coordination number 2 are linear



Four coordinate complexes are either square planar or tetrahedral



Six coordinate (octahedral) is the most prevalent


Isomers

Isomers – chemical compounds with the same formula but different structures.

Isomers can have different chemical and physical properties.


Linkage Isomers

Linkage isomers occur when a ligand can bond to a metal using either of two donor atoms.


Example 19 – 1 Isomers of Coordination Compounds

Draw ball-and-stick models of all possible isomers of the octahedral compound [Cr(NH3)3Cl3].


Naming Coordination Compounds

1. As with all salts, name the cation before the anion.2. Within the complex, first name the ligands in alphabetical order, and

then name the metal.3. 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)

4. 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.

5. If the coordination complex is an anion, add the suffix –ate to the stem name of the metal.

6. After the name of the metal, give the oxidation number of the metal in parentheses.



Latin Names of Metals in Anionic Complexes

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]


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)



Learning objective:

Use crystal field theory to explain the colour and magnetic properties of complexes



Crystal field theory – focuses on electrical interactions between a transition metal ion and its ligands.

Most accurately explains colour and magnetic properties.


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, .

The lower energy orbitals are called t2g and the higher energy orbitals are called eg


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 d-orbital, it is termed high-spin.

If the electron is paired with another electron, it is termed low-spin.


Example 19 – 4 Electron Configurations

Draw an energy level diagram and write the d electron configuration of [Pt(en)3]Cl2.


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.


Magnetic Susceptibility Balance


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 .


Contributions to Crystal Field Splitting Energy

Ligands play an important factor in the value of .The energetic effects of ligands are explained by the

spectrochemical series.

is also affected by the oxidation state and the position of the metal in the periodic table.


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+


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.


Relationships Among Wavelength, Colour, and Crystal Field Splitting Energy


Cr3+ Coordination Complexes


Example 19 – 7 Determining the Value of

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 in kilojoules per mole.


Square Planar Complexes


Tetrahedral Complexes


19.4 Transition Metals In Biology

Learning objective:

Explain the importance of transition metal complexes in biological processes


19.4 Transition Metals In Biology


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

2. 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.



Haemoglobin

Deoxyhaemoglobin Haemoglobin

Myoglobin


Also an O2 Transport protein


Ferritin

Iron Transport Protein

Contains 24 nearly identical polypeptides


Redox Proteins

Cytochrome c Plastocyanin

Learning objective:

Explain the chemistry of essential steps in the production of pure metals from ores


19.5 Metallurgy

Metallurgy – the production and purification of metals from naturally occurring ore deposits.


19.5 Metallurgy

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.


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.


Metallurgy of Transition Metals


Iron and Steel

Iron – the dominant structural material of modern times.

Steel – iron strengthened by additives (700 million tons/year).


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)


“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)


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)

4. 2 Cu2S (l) + 3 O2 (g) → 2 Cu2O (l) + 2 SO2 (g)

2 Cu2O (l) + Cu2S (l) → 6 Cu (l) + SO2 (g)


Impure copper, must be further refined

SO2 (g) waste!


Electrolytic Copper Production


Metal Mining in Canada


Learning objective:

Recognize the importance of transition metals in everyday life



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.


Chromium

0.012% of the Earth’s CrustDerived 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.


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.

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.


The Platinum Metals

Ru, Os, Rh, Ir, Pd and PtFound mingled together in ore depositsMost commonly used as catalysts



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Chapter 19. The Transition Metals 19.1 Overview of the Transition Metals 19.2 Coordination Complexes...

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