Topic 15 - Transition Metals Flashcards
What are transition metals?
d-block elements which can form one or more stable ions with incompletely-filled d-orbitals
-aka every d-block element except zinc and scandium
Why are zinc and scandium not transition metals?
- zinc’s ion Zn2+ has a full d-subshell
- scandium’s ion Sc3+ has an empty d-subshell
Why do transition metals show variable oxidation number?
they can form ions by loosing electrons from their 4s or 3d subshells
What is a ligand?
a molecule/negative ion with a lone pair of electrons which can form a dative bond with the empty, available d-orbitals of a transition metal
What is a complex ion?
a central transition metal ion surrounded by ligands
What is the coordination number (of a complex ion)?
the number of molecules/atoms a transition metal can datively bond to
-aka number of ligands
How do you name complex ions?
- number of ligands (di, tri, tetra, penta, hexa etc)
- ligand (aqua, ammine, hydroxo, chloro, fluoro, cyano, etc)
- name of transition metal (or latin for anionic complexes: chromate, ferate, cobaltate, aluminate, vandate, cuprate, etc)
What is a cationic complex?
a complex ion with a positive charge
What is an anionic complex?
a complex ion with a negative charge
What is a monodentate ligand?
a ligand with one long pair of electrons/that can form one dative bond
eg. Cl-, H20, CN-, NH3
What is a bidentate ligand?
a ligand with two long pairs of electrons/that can form two dative bonds
eg. NH2CH2CH2NH2 (1,2 diaminoethane)
What is a polydentate ligand?
a ligand with multiple long pairs of electrons/that can form multiple dative bonds
eg. EDTA2- (hexadentate ligand)
Where does the colour of transition metal ions and complex ions come from?
splitting of energy levels of the d-orbitals by ligands
- repulsion between the 3d electrons and the ligand’s lone pair of electrons increases the energy of the transition metal’s d-orbitals
- some d-orbitals rise in energy more than others, which creates a gap between the d-orbitals
- a particular wavelength of light is absorbed, which promotes electrons within the d-orbitals
- the complementary colour is reflected
Why do some aqueous transition metal ions and complex ions have a lack of colour?
no d-orbital electrons or d subshell is full so no electrons jump so no energy is absorbed
What could cause a change of colour in transition metal ions?
- change in oxidation number
- change in ligand
- change in coordination number
How is haemoglobin an example of a complex ion?
it is an iron (II) complex containing a multidentate ligand
-ligand exchange rxn occurs when an oxygen molecule bond to haemoglobin it replaced with a carbon monoxide molecule
What is the colour of the vanadium ion with an oxidation number of +5 aka VO2 +?
yellow
What is the colour of the vanadium ion with an oxidation number of +4 aka VO 2+?
blue
What is the colour of the vanadium ion with an oxidation number of +3 aka V3+?
green
What is the colour of the vanadium ion with an oxidation number of +2 aka V2+?
violet
How can Cr2O7 2- be reduced to Cr3+ and then reduced further to Cr2+?
using zinc (as reducing agent) in dilute acid
How can Cr3+ be oxidised to Cr2O7 2-?
using hydrogen peroxide in alkaline conditions followed by acidification
2CrO4 2− + 2H+ ⇌
Cr2O7 2− + H2O
What is observed when a little sodium hydroxide is added to chromium ions?
green solution changes to grey-green ppt
What is observed when a little ammonia is added to chromium ions?
green solution changes to grey-green ppt
What is observed when a little sodium hydroxide is added to iron(III) ions?
yellow solution changes to brown-red ppt
What is observed when a little ammonia is added to iron(III) ions?
yellow solution changes to brown-red ppt
What is observed when a little sodium hydroxide is added to iron(II) ions?
pale green solution changes to dark green ppt
What is observed when a little ammonia is added to iron(II) ions?
pale green solution changes to dark green ppt
What is observed when a little sodium hydroxide is added to cobalt ions?
pink solution changes to blue ppt
What is observed when a little ammonia is added to cobalt ions?
pink solution changes to blue ppt
What is observed when a little sodium hydroxide is added to copper ions?
blue solution changes to pale blue ppt
What is observed when excess sodium hydroxide is added to chromium ions?
green solution changes to grey-green ppt changes to green solution (ppt dissolves)
What is observed when excess ammonia is added to chromium ions?
green solution changes to grey-green ppt changes to purple solution (ppt dissolves)
What is observed when excess ammonia is added to cobalt ions?
pink solution changes to blue ppt changes to pale brown solution (ppt dissolves)
What is observed when excess ammonia is added to copper ions?
blue solution changes to pale blue ppt changes to dark blue solution (ppt dissolves)
What could lead to a change in coordination number?
-large uncharged ligands (eg. H2O) being substituted with small, charged ligands (eg. Cl-)
How does vanadium (V) oxide (V2O5) catalyse the contact process (SO2 + 1/2 O2 → SO3)?
acts as a heterozygous catalyst
- sulfur dioxide (SO2) is oxidised to SO3 by vanadium oxide, which reduces it vanadium (IV) oxide (V2O4)
- reduced catalyst is then oxidised back to vanadium (V) oxide
What are the two reactions showing how vanadium (V) oxide acts as a catalyst in the contact process (SO2 + 1/2 O2 → SO3)?
V2O5 + SO2 → V2O4 + SO3
V2O4 + 1/2 O2 → V2O5
How does a catalytic converter decrease carbon monoxide and nitrogen monoxide emissions from internal combustion engines?
- carbon monoxide and nitrogen monoxide absorb to surface of catalyst
- their bonds weaken
- carbon dioxide and nitrogen dioxide desorb from the surface of the catalyst
What are the reactions showing Fe2+ catalysing the reaction between I- and S2O8 2-?
S2O8 2- + 2I- → 2Fe3+ + 2SO4 -
2Fe3+ + 2I- → I2 + 2Fe2+
What is autocatalysis?
when a product catalyses its own reaction
-as conc of product increases, the rate of rxn increases
