Chapter 15: Transition Metals 15.1 General Properties of Transition Metals 15.2 Complex Formation and the Shape of Complex Ions 15.3 Coloured Ions 15.4 Variable Oxidation States of Transition Elements 15.5 Catalysis

15.1 General Properties of Transition Metals Learning 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] 4s 2 3d 1 Ti – [Ar] 4s 2 3d 2 V – [Ar] 4s 2 3d 3 Cr – [Ar] 4s 1 3d 5 Mn – [Ar] 4s 2 3d 5 Fe – [Ar] 4s 2 3d 6 Co – [Ar] 4s 2 3d 7 Ni – [Ar] 4s 2 3d 8 Cu – [Ar] 4s 1 3d10 Zn – [Ar] 4s 2 3d 10

Review: Electronic Configurations of Ions Write the electron configurations for the Sc 3+, the V 2+ and the Cu 2+ ions. Sc 3+ [Ar] V 2+ [Ar] 3d 3 Cu 2+ [Ar] 3d 9 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 Sc 3+ and Zn 2+ and neither of those ions contains a partially filled d-orbital. Sc 3+ [Ar] (empty d-subshell) Zn 2+ [Ar] 3d 10 (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 (H 2 O, NH 3 ). 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(H 2 O) 6 ] 2+ has a total charge of 2+). What is the charge of the metal ion in [Cu(H 2 O) 6 ] 2+ ? +2 = x + 0  x = +2  Cu 2+ 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(NH 3 ) 2 Cl 2 ] Tollen’s reagent [Ag(NH 3 ) 2 ] + Haemoglobin

Cis-platin [Pt(NH 3 ) 2 Cl 2 ] 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(NH 3 ) 2 ] + Linear shape. Distinguishes between aldehydes and ketones. Aldehydes reduce ion to Ag (silver mirror).

Haemaglobi n Contains a Fe 2+ ion which are hexa- coordinated (6 coordinate bonds). Four coordinate bonds are from nitrogens on the tetradentate ligand called porphyrin. The section containing the Fe 2+ 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?

Haemoglobi n The sixth bond is with water or oxygen. This is how oxygen is carried around the body through the blood. O 2 is not a very good ligand (weak bond with Fe 2+ ) so easily given up to cells. However, CO binds irreversible (forms stable complex) and destroys haemoglobin’s ability to carry oxygen.

15.3 Coloured Ions Learning 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?

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 States Learning 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 Co 2+ and Cr 3+ ions by water. 4.Recall the oxidation of Co 2+ 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 Fe 2+ ions reacting with Cl 2 gas to form Fe 3+ 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 Fe 2+  Fe 3+ + e - Cl 2 + 2e -  2Cl - Balanced Redox Equation 2Fe 2+ (aq) + Cl 2 (g)  2Fe 3+ (aq) + 2Cl - (aq) Fe 2+ is oxidised (+2  +3), Cl 2 is reduced (0  -1) Cl 2 is the oxidising agent and Fe 2+ is the reducing agent.

Potassium manganate (VII) can act as an oxidising agent in acidic conditions (H + aqueous). KMnO 4 MnO 4 - is reduced to Mn 2+ Write the balanced redox equation for Fe 2+ being oxidised to Fe 3+ by potassium manganite (VII) in acidic conditions.

Potassium manganite (VII) is soluble so forms K+ and MnO4- ions. MnO e -  Mn 2+ (+7  +2) MnO H + + 5e -  Mn H 2 O Fe 2+  Fe 3+ + e - (+2  +3) 5Fe 2+  5Fe e - MnO Fe H +  Mn Fe H 2 O

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 ions Oxidation StateFormula of IonColourStable In +6Cr 2 O 7 2- (dichromate) OrangeAcid +6CrO 4 2- (chromate) YellowAlkali +3Cr 3+ Green/Violet +2Cr 2+ Blue

Reactions with Chromium Ions