Transition Metals: Edexcel A-level Chemistry

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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 :
○NH2CH2CH2NH2 (1,2-diaminoethane)

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

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