Chemistry of the D-Block Transition Metals
Adsorption
The process by which reactants form bonds to the surface of a solid catalyst. This weakens the covalent bonds in the reactants and brings them closer together, allowing the reaction to occur more easily.
Catalyst
A substance that speeds up the rate of a reaction without being used up.
Catalytic Activity of Transition Metals
Due to transition metals having variable oxidation states they can catalyse other reactions by acting as an oxidising/reducing agent.
Colours in Transition Metal Complexes
Colour arises when some of the wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected. The d-orbital electrons move from ground state to an excited state when light is absorbed.
Complex Ion
An ion which has a central metal atom (typically a transition element) surrounded by ligands. The ligands are bound to the transition metal centre by dative coordinate bonds.
Coordination Number
The number of dative covalent bonds formed with the central metal ion.
Dative Covalent (Coordinate) Bond
A type of covalent bond in which one bonding atom provides both electrons in the bonding pair.
D-Block
The block of elements in the middle of the periodic table. Most d-block elements are transition metals. Elements in the d-block have their outer electron in the d orbital.
Heterogenous Catalysts
In a different phase or state to the species in the reaction.
Homogenous Catalysts
In the same phase or state as the species in the reaction.
Hydrogenation
A reaction between H2 and another substance, often reduces or saturates a compound. These reactions usually require a catalyst like nickel.
Ligand
An atom, ion or molecule that forms a coordinate bond with a central transition metal ion by donating a pair of electrons.
Ligand Exchange
A reaction in which one ligand in a transition metal complex is replaced by another. Typically, these reactions are associated with a colour change.
Octahedral
The shape of a transition metal complex with a coordination number of 6 and a bond angle of 90 degrees, e.g. [Cu(H2O)6]2+.
Oxidation State
The charge of an ion or a theoretical charge of an atom in a covalently bonded compound assuming the bond becomes ionic.
Splitting of D-Orbitals
When a ligand forms a bond with a central metal ion it affects the d-orbitals differently depending on how they are arranged in space. Consequently the d-orbitals split into two sets of degenerate (same energy) orbitals; in octahedral complexes there are two orbitals that are higher in energy and three that are lower, in tetrahedral complexes there are three orbitals higher and two lower.
Tetrahedral
One of the possible shapes of a transition metal complex with a coordination number of 4 and a bond angle of 109.5 degrees, e.g. CuCl42-.
Transition Metal Elements
D-block elements that can form one or more stable ions with an incomplete d-subshell. Transition elements have more than one oxidation state, form coloured ions and can often act as catalysts.
Variable Oxidation States
Due to transition metals having incomplete d-subshells they have the ability to have variable stable oxidation states. This is due to the 4s and 3d subshells being similar ion energies.