Transition Metals Flashcards
What is a heterogenous catalyst and how do they work ?
-Heterogeneous catalysts are in a different state to the reactants.
-Heterogeneous catalysis can be explained in terms of the formation of activated complexes and the adsorption of reactive molecules onto active sites. The presence of unpaired d electrons or unfilled d orbitals is thought to allow activated complexes to form. This can provide reaction pathways with lower activation energies compared to the uncatalysed reaction.
What is a homogenous catalyst and how do they work ?
Homogeneous catalysts are in the same state as the reactants.
Homogeneous catalysis can be explained in terms of changing oxidation states with the formation of intermediate complexes.
What can act as catalysts ?
Transition metals and their compounds can act as catalysts.
What are the d-block transition metals
Metals with an incomplete d-subshell in at least one of their ions and can have different oxidation states in its compounds.
How are d-orbitals filled in transition metals ?
-The filling of the d orbitals follows the Aufbau principle, with the exception of chromium and copper atoms.
-These exceptions are due to the special stability associated with the d subshell being half-filled or completely filled.
What can cause compounds of the same transition metal to have different colours ?
Compounds of the same transition metal in different oxidation states may have different colours.
What are ligands ?
-Ligands may be negative ions or molecules with non-bonding pairs of electrons that they donate to the central metal atom or ion, forming dative covalent bonds.
-Ligands can be classified as monodentate, bidentate, up to hexadentate.
What is coordination number
The total number of bonds from the ligands to the central transition metal is known as the coordination number.
what is d orbital splitting
-In a complex of a transition metal, the d orbitals are no longer degenerate.
-Splitting of d orbitals to higher and lower energies occurs when the electrons present in approaching ligands cause the electrons in the orbitals lying along the axes to be repelled (dx^2-y^2 and dz^2)
Describe ligands in splitting
-Ligands that cause a large difference in energy between subsets of d orbitals are strong field ligands. Weak field ligands cause a small energy difference.
-Ligands can be placed in an order of their ability to split d orbitals; this is called the spectrochemical series.
How does colour arise in a transition metal complex ?
-Colours of many transition metal complexes can be explained in terms of d-d transitions.
-Light is absorbed when electrons in a lower energy d orbital are promoted to a d orbital of higher energy.
-If light of one colour is absorbed, then the complementary colour will be observed.
-Electrons transition to higher energy levels when energy corresponding to the ultraviolet or visible regions of the electromagnetic spectrum is absorbed
