Transition metals as catalysts Flashcards
What is the definition of a transition metal?
A metal with an incomplete ( or partially full ) d sub shell in at least one of their ions.
Why is zinc no considered a transition metal?
Zn 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10
Zn can only form a +2 ion
Loses 4s electrons first and its left with a full d orbital
Transition metal is a metal with an icomplete d sub shell in at least one of their ions.
Zn has a complete d orbital in its ion so doesn’t not meet the criteria to be a transition metal.
How does colour arise in a complex?
Colour raised from electron transitions from the ground state to excited state between different d orbitals.
A portion of visible light is absorbed to promote d electrons to higher energy levels. The light that is not absorbed is transmitted to give the substance colour.
How do you change the colour of a complex?
Changing a ligand or changing the coordination number will alter the energy split between the d orbitals changing the energy difference and hence the frequency of light absorbed.
What are the two types of catalysts?
Heterogeneous and Homogenous.
What is a heterogenous catalyst?
they are in a different physical state to the reactants.
What is a homogenous catalyst?
They are in the same physical state as the reactants.
Why can transition metals act as catalysts?
The presence of unpaired d electrons or unfilled d orbitals is thought to allow intermediate complexes to form. This can provide reaction pathways with lower activation energies compared to the uncatalysed reaction.
What is ‘adsorption’?
the ‘sticking’ of a molecule onto the surface of a catalyst. The surface metal atoms are able to bond onto molecules because they form less bonds in the metallic structure.
How can heterogenous catalysts be described?
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.
How can homogenous catalysts be explained?
Can be explained in terms of changing oxidation states with the formation of intermediate complexes.
