Transition metals
A transition metal is a metal that can have at least one oxidation state with an electron in the d-orbital. According to this definition Scandium and Zinc are not transition metals because both Sc3+ and Zn2+ do not have electrons in their d orbitals.
It must be noted that this is different from the d-block elements which means that the last electron is put in a d-orbital.
Oxidation state
All transition elements lose the 2 electrons found in the s orbitals to produce a 2+ ion. Apart from this, they can also lose electrons from the d-orbital, since these would have similar ionisation energies. Manganese can have a maximum oxidation state of +7 since it is 4s2 3d5 and therefore it has 5 unpaired electrons in the d-orbitals.
Catalytic properties
Heterogeneous catalysts
A heterogeneous catalyst is a catalyst that is in a different state to the reactants, for example, a solid in a solution mixture. This normally offers an adsorption surface where the reaction can take place, just like Iron in the preparation of ammonia.
Homogenous catalysts
A homogeneous catalyst is one which is in the same state as the reaction mixture. In this case, transition metals can use their variable oxidations states. One such reaction is the reaction between iodide ions and thiosulfate.
Coloured compounds
When transition metals form ligands the overlapping of the orbitals do not remain degenerate, producing 2 different energy states. This is due to the interaction between the orbitals of the ligands with the d-orbital of the transition metal.
Compounds as listed in the syllabus
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- Mn2+: Oxidation State: +2 Colour: pink
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- MnO2: Oxidation State: +4 Colour: black
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- MnO42-: Oxidation State: +6 Colour: green
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- MnO4–: Oxidation State: +7 Colour: purple
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- Fe2+: Oxidation State: +2 Colour: green
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- Fe3+: Oxidation State: +3 Colour: brown
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- Cu+: Oxidation State: +1 Colour: white
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- Cu2+: Oxidation State: +2 Colour: blue
Coordinating Compounds
When it comes to transition metals they have the ability to form bonds with ligands in order to form complexes. A complex is formed when a central atom is surrounded by ligands through a dative bond.
- Central Atom: The atom in the middle of the complex. In the case of coordination compounds, this would be the transition metal/ion
- Ligand: A molecule or anion that is bonded through a dative bond with a central atom in a complex. This has to be a nucleophile.
- Complex/Coordinated Compound: A central atom surrounded by ligands.
Complex Ions to be studied:
[Fe(H2O)6]2+
The oxidation number of Fe in [Fe(H2O)6]2+ is +2
[Zn(NH3)4]2+
The oxidation number of Fe in [Zn(NH3)4]2+ is +2
[Cu(NH3)4]2+
The oxidation number of Fe in [Fe(H2O)6]2+ is +2
[CuCl2]–
The oxidation number of Fe in [CuCl2]– is +1
[Fe(CN)6]3-
The oxidation number of Fe in [Fe(CN)6]3- is +3