Transition Metals Flashcards
What are the characteristics of a transition metal
•complex formation,
•formation of coloured ions,
•variable oxidation state
•catalytic activity.
incomplete d sub-level in atoms or ions
Why is zinc not a transition metal
Zinc can only form a +2 ion.
In this ion the Zn2+ has a complete d orbital and so does not meet the criteria of having an incomplete d orbital in one of its compounds.
What is a complex
is a central metal ion surrounded by ligands.
What is co ordinate bonding
Co-ordinate bonding is involved in complex formation.
Co-ordinate bonding is when the shared pair of electrons in the covalent bond come from only one of the bonding atoms
What is a ligand
an atom, ion or molecule which can donate a lone electron pair.
Examples of monodentate ligand
e.g. H2O, NH3 and Cl- )
What is a monodentate ligand
Only forms one coordinate bond per ligand
Describe Bidentate ligand
NH2CH2CH2NH2 and ethanedioate ion C2O4 2- )
which have two atoms with lone pairs and can form two coordinate bonds per ligand,
What is a multi dentate ligand
multidentate (e.g. EDTA4- which can form six coordinate bonds per ligand).
Describe substitution reactions for NH3 and H2O
The ligands NH3 and H2O are similar in size and are uncharged.
Exchange of the ligands NH3 and H2O occurs without change of co-ordination number
[Co(H2O)6]2+(aq) + 6NH3 (aq) -> [Co(NH3)6]2+(aq) + 6H2O (l
Describe the reaction of chloride ions
The Cl- ligand is larger than the uncharged H2O and NH3 ligands so therefore ligand exchange can involve a change of co-ordination number.
Describe the chelate effect
The substitution of minodentate ligand with bidentate or multidentate ligand leads to a more stable complex
Can be explained in terms of positive entropy change as there are molecules of products than reactants
What is EDTA used for
Added to rivers to remove poisonous heavy metal ions as the EDTA complexes are not toxic
How does colour change arise
Change in
1. Oxidation state
2. Coordination number
3. Ligand
How does colour arise in transition metals
Electronic transitions from the ground state to excited states
- A portion of visible light is absorbed
- This promotes d electrons to a higher energy level
- Light that is not absorbed is transmitted to give the substance colour
Equation for colour
/\E= hv
/\E=hc/ y
What element doesn’t have colour
Scandium
what are the relative trends for transition metals as oxidising agents
*Relative stability of +2 state with respect to +3 state increases
across the period
*Compounds with high oxidation states tend to be oxidising agents
e.g. MnO4
- *Compounds with low oxidation states are often reducing agents e
what are the main oxidaion states for vanadium
VO2+ Oxidation state +5 ( a yellow solution)
VO^2+ Oxidation state + 4 (a blue solution)
V^3+Oxidation state + 3 (a green solution)
V^2+Oxidation state + 2 (a violet solution)
what is tollens reagent
[Ag(NH3)2]+
is used in Tollens’ reagent to distinguish between aldehydes
and ketones
what is half equation for manganate
MnO4-(aq) + 8H+
(aq) + 5Fe2+ (aq) –> Mn2+ (aq) + 4H2O (l) + 5Fe3+
what is half equation for ethanedioate
C2O42- –>2CO2 + 2e-
what is a heterogenous catalyst
A heterogeneous catalyst is in a different phase from the reactants
Describe adsorption
Adsorption of reactants at active sites on the
surface may lead to catalytic action.
The active site is the place where the reactants adsorb onto the
surface of the catalyst.
This can result in the bonds
within the reactant molecules becoming weaker
There will also be a higher concentration of reactants
at the solid surface, so leading to a higher collision
frequency.
what is the process of heterogeneous catalyst
Reactants adsorb onto the surface
Bonds weaken
Products desorb
Large surface area using powder pellets
Catalyst poisoned
Active sites blocked
how is V2O5 a catalyst in the Contact process.
step 1
SO2 + V2O5 –> SO3 + V2O4
step 2
2V2O4 + O2 –> 2V2O5
what is a homogeneous catalyst
a catalyst which is in the same phase as the reactants
how does Fe speed up the reaction
The uncatalysed reaction is very slow because the reaction
needs a collision between two negative ions.
Repulsion between the ions is going to hinder this – meaning high
activation energy
the Fe reduces repulsion between negatively charged ions
How can transition metals be homogeneous catalyst
because they can form various oxidation states.
They are able to donate
and receive electrons and are able to oxidize and reduce.
This is because the ions contain partially filled sub-shells of d
electrons that can easily lose or gain electrons.
what are the half equations for the homogeneous catalysts
stage 1
S2O82- + 2Fe2+ –> 2SO4 2- + 2Fe3+
stage 2
2I- + 2Fe3+ –> 2Fe 2+ + I2
what is autocatalysis
autocatalysis where one of
the products of the reaction can catalyse the
reaction.
what are the half equations for autocatalysis
Step 1 4Mn2+ + MnO4
- + 8 H+–> 5Mn3+ + 4 H2O
Step 2 2Mn3+ + C2O4 2- –> 2Mn2+ + 2 CO2
how does Mn2+ act as an autocatalysis
The initial uncatalysed reaction is slow because the reaction is a
collision between two negative ions
which repel each other
leading to a high activation energy.
The Mn2+ ions produced act as an autocatalyst and therefore the reaction starts to speed up because they bring about the
alternative reaction route with lower activation energy.
Explain why an aqueous solution containing [Fe( H2O )6]3+ has a lower PH than solution containing [Fe(H2O)62+
Fe 3+ has greater charge
Fe3+ is more polarising so more O-H bonds break
