Transition Metals Flashcards
Define what a d block element is
Outer electrons are found in d - orbitals
Define transition metals
A metal that passes a partially filled d-sub shell in its atom or stable ions
Define co-ordinate bonding
Both electrons in the bond come from same species
What is a monodentate ligand ?
A ligand that has 1 atom that can bond to the metal ion
What is a bidentate ligand ?
A ligand that has 2 atoms that can bond to the metal ion.
What is ligand exchange ?
When a transition metal ion is exposed to a mixture of ligands, the ligands can be exchanged to form a new complex. This is an equilibrium process
Which 2 elements in the d-block are not technically transition metals ?
Scandium and Zinc
They do not form ions with an incomplete d-sub shell
Which 2 elements are the exception to the rule that the 4s orbital is filled before the 3p orbital?
Chromium and copper
What are the general properties of transition metals?
— They have variable oxidation states
- Form complex ions
- Form coloured ions in solution
- Can catalyse reactions either as elements or in compounds
Give examples of transition metals that have variable oxidation states
Iron (Fe) ll and lll
Copper (Cu) l and ll
Chromium (Cr) ll and lll
Why do transition metals have variable oxidation states?
Variable oxidation states arise because the electrons in the 4s and 3d orbitals have similar energies. This means that a relatively similar amount of energy is required to gain or lose different numbers of electrons
What colour are aqueous solutions of compounds containing Cr3+ ions?
Green
What is a complex ion?
A complex ion is a central metal ion surrounded by ligands
What is meant by coordination number?
The number of dative bonds formed with a central metal ion
Why do transition metals form coloured complexes?
When visible light hits, electrons are excited to a higher energy levels. Some frequencies of the visible light are absorbed when electrons jump to a higher energy orbitals
What can lead to a colour change in a transition metal complex?
Change in oxidation number of the ion
Change in the ligand
Change in coordination number of the complex
What is the shape and bond angle of the ion with a coordination number of 4?
Tetrahedral
109.5
What shape and bond angle does an ion produce with a coordination number of 6?
Octahedral
90
What is a ligand exchange reaction?
A ligand exchange is a chemical reaction involving the replacement of ligands in a complex by a different set of ligands. This is an equilibrium process
What is the difference in a homogeneous and heterogeneous catalyst?
Homogeneous = in the same phase as the reactants and takes place via intermediate species
Heterogeneous = different phase to the reactants occurring on the surface of the catalyst
Why do transition metals make good homogeneous catalysts?
Transition metals have variable oxidation states. This means they are able to oxidise and reduce reactants and intermediates to form the desired products
Why do transition metals make good heterogeneous catalysts?
Provide a surface for molecules to be absorbed and come closer together for reaction. Molecules can form coordinate bonds to the metal atom because there are empty d orbitals to accept electron pairs due to the d orbitals only being partially filled
What catalyst is used in the hydrogenation of Alkenes?
nickel
Heterogeneous
Define standard electrode potential
The potential difference between the standard hydrogen electrode and the half cell which is connected to it
