Chapter 15: Transition Metals15.1 General Properties of Transition Metals15.2 Complex Formation and the Shape of Complex Ions15.3 Coloured Ions15.4 Variable Oxidation States of Transition Elements15.5 Catalysis

15.1 General Properties of Transition MetalsLearning Objectives:1. Recall the general properties of transition metals.2. Explain these properties in terms of electronic structure.

Review: Electron Configuration• Write out the electron configurations for the Period 4 d-block

elements (Sc to Zn). Use the noble gas abbreviation.

Sc – [Ar] 4s2 3d1

Ti – [Ar] 4s2 3d2

V – [Ar] 4s2 3d3

Cr – [Ar] 4s1 3d5

Mn – [Ar] 4s2 3d5

Fe – [Ar] 4s2 3d6

Co – [Ar] 4s2 3d7

Ni – [Ar] 4s2 3d8

Cu – [Ar] 4s1 3d10Zn – [Ar] 4s2 3d10

Review: Electronic Configurations of Ions• Write the electron configurations for the Sc3+, the V2+ and the Cu2+

ions.

• Sc3+ [Ar] • V2+ [Ar] 3d3

• Cu2+ [Ar] 3d9

Remember:Always form positive ions.S-block electrons always lost first.

Transition Metals

Transition Metal = a metal that can form one or more stable ions with a partially filled d-subshell

Scandium and Zinc are NOT transition metals

• Scandium and Zinc are not considered transition metals, even though they are d-block metals, because they only form one stable ion Sc3+

and Zn2+ and neither of those ions contains a partially filled d-orbital.

• Sc3+ [Ar] (empty d-subshell)• Zn2+ [Ar] 3d10 (full d-subshell)

Physical Properties (Metallic Properties)• Good conductors of heat and electricity• Hard• Strong• Shiny• High melting and boiling points

Low Reactivity• Physical properties and fairly low reactivity makes them very useful

materials.

Examples:• Iron (and alloy steel) useful as a building material for high strength.• Copper for water pipes and electrical wires• Titanium for jet engine parts (withstands high temperatures)

Special chemical properties are caused by partially filled d-subshells• Variable Oxidation States – the 4s and 3d energy levels are

very close together, so different amounts of electrons can be lost using similar amounts of energy• Coloured – transition metal ions are coloured• Catalysis – they are good catalysts as can easily go between

two stable ions• Complex Formation

15.2 Complex formation Learning Objectives:1. Describe the formation of complex ions.2. Determine the shape of complex ions.3. Draw structure of complex ions.4. Determine the charge of complex ions.

Formation of Complex Ions• Complex ion = a metal ion surrounded

by coordinately bonded ligands.

• Coordinate bond (dative covalent bond) = a covalent bond in which both electrons in the shared pair come from the same atom

• Ligand = an ion or molecule that donates a pair of electrons to a central metal ion.

Shape of Complex Ion• Coordination number

determines the shape of a complex ion.

• Coordination number = the number of coordinate bonds to ligands in a complex ion

Transition metal ions commonly form

octahedral complexes with small ligands (H2O,

NH3).

Transition metal ions commonly form

tetrahedral complexes with larger ligands (Cl-)

This is because fewer ligands fit around the

central metal ion.

Multidentate ligands• Ligands that can only form one bond are called unidentate.• Some ligands can attach to the metal ion more than once. • These are called multidentate ligands.• They have multiple lone pairs that can be donated to the metal ion.

• Bidentate ligands = form two coordinate bonds with metal ion• Tridentate ligands = form three• Tetradentate ligands = forms four

Oxidation States• The total oxidation state of the complex ion is placed outside square

brackets (Example: [Cu(H2O)6]2+ has a total charge of 2+).

• What is the charge of the metal ion in [Cu(H2O)6]2+ ?• +2 = x + 0 x = +2 Cu2+

Total Oxidation State of Complex Ion

Oxidation State of the Metal Ion

Sum of Oxidation States of Ligands

Examples of Complex Ions (that you need to know)• Cis-platin [Pt(NH3)2Cl2]• Tollen’s reagent [Ag(NH3)2]+

• Haemoglobin

Cis-platin• [Pt(NH3)2Cl2]• Square planar shape• Cis (The chlorines are on the same

side)• Successful anti-cancer drug

• Trans-platin interestingly has no anti-cancer properties.

Tollen’s Reagent• Contains complex ion [Ag(NH3)2]+

• Linear shape.• Distinguishes between aldehydes

and ketones.• Aldehydes reduce ion to Ag (silver

mirror).

Haemaglobin

• Contains a Fe2+ ion which are hexa-coordinated (6 coordinate bonds).• Four coordinate bonds are from

nitrogens on the tetradentate ligand called porphyrin.• The section containing the Fe2+

surrounded by the nitrogen porphyrin ring is called “haem”.• A fifth nitrogen is attached to a

larger protein called “globin”.• What is the sixth bond?

Haemoglobin

• The sixth bond is with water or oxygen.• This is how oxygen is carried

around the body through the blood.• O2 is not a very good ligand

(weak bond with Fe2+) so easily given up to cells.• However, CO binds irreversible

(forms stable complex) and destroys haemoglobin’s ability to carry oxygen.

15.3 Coloured IonsLearning Objectives:1. Describe the factors that determine the colour of a complex ion.2. Link the colour to electronic configuration.

Why are transition metal ions coloured?• Part filled d-orbitals• Possible for electrons to move from one d-orbital to another.• Compounds have d-orbitals of slightly different energy levels.• Electrons absorb energy and move up to a higher energy level.• Wavelength of the energy is equal to the difference in energy.• This wavelength of light is removed and the other colours are

reflected (the colour you see).

Amount of energy

ΔE = hν

• ΔE : amount of energy• h = Planck’s constant• ν = frequency of light absorbed

What colour?• Large energy gap Higher frequency of

light Violet absorbed • Complementary colour reflected: • Appears Yellow

• Small energy gap Lower frequency Red is absorbed• Complementary colour reflected:• Appears Green

What affects the colour?•Metal Ion•Oxidation State•Coordination number•Ligands

• Spectrometry can be used to determine the concentration of a solution by measuring how much light it absorbs.• Filter is used to only allow through the colour of light absorbed by the

substance being tested.• A colorimeter detects how much light has been absorbed and the

concentration of the sample can be calculated.

Calibration graph• Solutions of known

concentration are tested.• The results are plotted on

a calibration graph.• The concentration of the

unknown sample can then be predicted using the calibration graph.

15.4 Variable Oxidation StatesLearning Objectives:1. Recall that transition elements have variable oxidation states.2. Recall the equilibrium reaction between chromium, chromate (VI)

ions and dichromate(VI) ions.3. Recall the oxidation reaction of Co2+ and Cr3+ ions by water.4. Recall the oxidation of Co2+ ions by air.5. Represent these equations using half equations.

Redox of Transition Elements• Transition elements commonly undergo redox reactions as they have

more than one stable ion.

Example:• Write out the half equation for Fe2+ ions reacting with Cl2 gas to form

Fe3+ ions and Cl- ions.• Write out the balanced redox reaction.• What is oxidised? What is reduced?• What is the oxidising agent? What is the reducing agent?

Half Equations• Fe2+ Fe3+ + e-

• Cl2 + 2e- 2Cl-

Balanced Redox Equation• 2Fe2+

(aq) + Cl2 (g) 2Fe3+ (aq) + 2Cl- (aq)

• Fe2+ is oxidised (+2 +3), Cl2 is reduced (0-1)• Cl2 is the oxidising agent and Fe2+ is the reducing agent.

• Potassium manganate (VII) can act as an oxidising agent in acidic conditions (H+ aqueous).

• KMnO4

• MnO4- is reduced to Mn2+

• Write the balanced redox equation for Fe2+ being oxidised to Fe3+ by potassium manganite (VII) in acidic conditions.

• Potassium manganite (VII) is soluble so forms K+ and MnO4- ions.

• MnO4- + 5e- Mn2+ (+7 +2)

• MnO4- + 8H+ + 5e- Mn2+ + 4H2O

• Fe2+ Fe3+ + e- (+2 +3)• 5Fe2+ 5Fe3+ + 5e-

• MnO4- + 5Fe2+ + 8H+ Mn2+ + 5Fe3+ + 4H2O

Redox Titrations• Redox reactions can be used instead of neutralisation reactions in a

titration to determine the concentration of an oxidising or reducing agent in solution.

• Acidified potassium manganate(VII) (oxidising agent) can be used to react with a reducing agent to determine it’s concentration.• Potassium manganate(VII) is deep purple and is used to self indicate as

the purple colour disappears when the ions are reduced.• If the purple colour remains, that means that all the reducing agent

has been oxidised (leaving leftover oxidising agent).

Chromium ionsOxidation State Formula of Ion Colour Stable In

+6 Cr2O72-

(dichromate)Orange Acid

+6 CrO42-

(chromate)Yellow Alkali

+3 Cr3+ Green/Violet

+2 Cr2+ Blue

Reactions with Chromium Ions