Transition Metals: Edexcel A-level Chemistry
|Transition element;||A d-block element that forms one or more ions with an incomplete d sub-shell.|
|Complex ion;||A transition metal ion bonded to one or more ligands by coordinate bonds.|
|Ligand;||A molecule or ion that can donate a pair of electrons with the transition metal ion to form a coordinate bond.|
|Coordinate number;||The total number of coordinate bonds formed between a central metal ion and its ligands.|
|Stereoisomers;||Are species with the same structural formula but with a different arrangement of atoms in space.|
|Ligand substitution;||A reaction in which one ligand in a complex ion is replaced by another ligand.|
|Stability constant, K(stab);||The equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution.|
|Oxidation;||Loss of electrons or increase in oxidation number|
|Reduction;||Gain of electron of decrease in oxidation number|
|d-block element||(as opposed to a transition element) are elements where the last electron has gone into a d-orbital|
|electron configuration rules & evidence|| First electrons lost are from the 4s orbital, then from paired electrons in the 3d orbital.|
Jump in 2nd and 3rd ionisation energies (n.b. jump between 1st and 2nd for Cr and Cu). Another jump after last 3d-electron has been removed.
|Properties of Transition Elements|| ☺Variable Oxidation State|
☺Form Coloured, Complex Ions
|Monodentate Ligands|| Use 1 pair of electrons to form dative covalent bond with the metal ion. E.g. :|
○ H2O, NH3, Cl-,CN-
○NB max.no. of Cl-ions=4 (as they are bigger than water molecules)
|Bidentate Ligands|| use 2 pairs of electrons to form 2 dative covalent bonds with the metal ion E.g :|
|Polydentate Ligands|| Eg|
○EDTA (4- ion) can for 6 ligands.
○ haemoglobin contains Fe ion complexed with a pentadentate ligand occupying 5 sites with an oxygen atom in the 6th.
|Shape of Complex Ion|| 6-coordinate bond: octahedral (90 ۫ bond angles)|
6 bond pairs repel each other to a position of maximum separation.
4 coordinate bonds: tetrahedral/ square planar (platinum NH3 Cl2)
2 coordinate bonds: linear
|Catalytic Activity||Transition Metals use their d-orbitals to provide active site on their surfaces to which reactants bond.|
|Disproportionation||When an element in a single species is simultaneously oxidised and reduced.|
|Ligand Exchange||When one ligand either totally or partially replaces the ligand in a complex (eg adding excess NH3)|
|Deprotonation||When complex loses its +ve charge E.g when adding NaOH or a few drops of NH3|