2.5 Transition Metals Flashcards
what is a transition metal?
- a metal that can form one or more stable ions with a partially filled d sub-level
give the electron configuration of Ti and Ti3+ to prove this
Ti : 1s2 2s2 2p6 3s2 3p6 4s2 3d 2
Ti 3+ : [ Ar ] 4s0 3d1
why is zinc not a transition metal?
- it forms an ion which has a full d sub level
what is a complex?
- central metal ion surrounded by ligands
what is a ligand?
- an atom, ion or molecule which can donate a lone pair of electrons to the central metal ion
what is co-ordination number?
- number of co-ordinate bonds formed to central metal ion
what is co-ordinate bonding?
- when the shared pair of electrons in the covalent bond comes from only one of the bonding atoms
what are monodentate ligands?
- ligands which can form one co-ordinate bond per ligand
what are bidentate ligands?
- ligands which can form two co-ordinate bonds per ligand
what are multidentate ligands
- ligands which can form six co-ordinate bonds per ligand
why is carbon monoxide toxic to humans?
- CO can form a strong co-ordinate bond with haemoglobin
- this replaces oxygen, causing carbon monoxide poisoning
what is the chelate effect?
the substitution of a monodentate ligand with a bidentate or multidentate ligand leads to stability
explain how entropy works with chelate effect
- when a substitution reaction occurs involving a ligand being replaced by a higher tier ligand, more moles of products are formed
- increase in entropy so increase in GFE, so complex is more likely to form, hence become more stable
why is the enthalpy change close to zero in a ligand sub reaction?
- number of dative covalent bonds and type, are the same
- energy required to break and make bonds will be the same
what are cis and trans isomers?
cis - Z - same
trans - E - different
how does E-Z isomerism occur in complexes
- there is restricted ligand movement around the central atom
- two different ligand types required to form E-Z
what shapes tend to show cis trans isomerism
- square planar
- octahedral
what are the key rules to remember for optical isomerism of complexes?
- 3 bidentate ligands are always optically active
- 2 bidentate ligands and 2 monodentate ligands only the cis form is optically active
- no optical isomerism for monodentatw
how does colour change arise?
change in :
- oxidation state
- co-ordination number
- ligand
how do ligands create a colour?
- negatively charged ligand approaches d orbital
- d orbitals split into two different energy levels due to electron repulsion
- an electron absorbs energy ( hf ) from visible light to jump from lower energy orbital to higher energy orbital
- absorbed energy corresponds to a specific wavelength of light
- color you see is the complentary colour
what does energy gap depend on?
- changing a ligand, can cause larger splitting, so different energy absorbed
- metal ion, different energy gap levels
- oxidation state, higher cause larger splitting
why do some complexes have no colour?
- d orbitals are either completely full or completely empty
- some complexes have a very large energy gap, pushing required energy into UV range, meaning no visible light is absorbed
whats the spectrophotometry method
- add an appropriate ligand to intensify colour
- make up solutions of known concentration
- measure absorption vs concentration
- plot graph of absorption vs concentration
- measure absorption of unknown and compare
how do catalysts increase reaction rates?
- they provide an alternate pathway with a lower activation energy
what is a heterogenous and a homogenous catalyst?
- heterogenous is a catalyst that is in a different phase from the reactants
- homogenous is a catalyst that is in the same phase as the reactants
how do heterogenous catalysts work?
- reactant molecules adsorb onto the surface of the solid catalyst, weakening bonds and increasing their reactivity
- adsorbed molecules react more easily, forming an intermediate that lowers activation energy
- product molecules leave surface, freeing up active sites for more reactants
- catalyst is not used up and can be reused continuously
