Chapter 24 - Transition Elements Flashcards
What is the role of cis-platin in medicine
It is an anticancer drug and it does this by binding to DNA preventing cell division
What is a ligand-substitution reaction?
A reaction where one one ligand in a complex ion is replaced by another ligand
When copper(II) sulfate is dissolved in water what complex is formed and what colour is this?
[Cu(H2O)6]2+ is formed in aqueous solution and it is pale blue
What is formed when aqueous ammonia is added dropwise to [Cu(H2O)6]2+ ?
What is the colour change?
Describe this reaction
Starts as a pale blue solution, then a pale blue ppt is formed - Cu(OH)2 and then a dark blue solution is formed - [Cu(NH3)4(H2O)2]2+ (aq)
In this reaction four of the water ligands are replaced by four of the ammonia ligands
What is formed when hydrochloride acid is added to [Cu(H2O)6]2+ ?
What is the colour change?
Describe this reaction
Original solution is pale blue but [CuCl4]2- is yellow. However a reversible reaction means the reaction mixture is green
Six water ligands have been replaced by four chloride ligands
What complex is formed when chromium is dissolved in water and what is the colour of the solution?
[Cr(H2O)6]3+ and this is a pale purple solution
What happens when ammonia is added dropwise to [Cr(H2O)6]3+?
1) Initially a grey-green ppt is formed of Cr(OH)3
2) The Cr(OH)3 ppt dissolves in excess ammonia to form the complex ion to form [Cr(NH3)6]3+ (a purple solution)
Why is the iron in haemoglobin so important?
The central metal ion in a haem group, Fe2+, can bind to oxygen and carry it round the body
Describe ligand substitution of haemoglobin
In the lungs the haemoglobin can bond to oxygen, forming oxyhaemoglobin which release oxygen to body cells when required
If CO is breathed in a ligand substitution can take place where oxygen is replaced by carbon monoxide and carbon monoxide bonds more strongly than oxygen (prevents haemoglobin from carrying oxygen)
What colour changes take place when aqueous Cu2+, Fe2+, Fe3+ and Mn2+ are reacted with aqueous sodium hydroxide?
Cu2+ : Blue solution reacts to form blue ppt
Fe2+ : Pale green solution reacts to form a green ppt
Fe3+ : Pale yellow solution reacts to form an orange-brown ppt
Mn2+ : Pale pink solution reacts to form a light brown ppt
All insoluble in excess NaOH
E.g Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
What happens when Mn(OH)2 and Fe(OH)2 are left to stand in air?
Mn(OH)2 : light brown ppt darkens
Fe(OH)2 : green ppt gets brown on surface as iron(II) is oxidised to iron (III)
What happens when sodium hydroxide is added to Cr3+ ions?
Violet solution reacts to form a grey-green ppt - Cr(OH)3
Ppt is soluble in excess of sodium hydroxide forming a dark green solution [Cr(OH)6]3-
Precipitation reactions of Cu2+, Fe2+, Fe3+, Mn2+ and Cr3+ with ammonia?
Cu2+ : Cu(OH)2 dissolves in excess ammonia to form [Cu(NH3)4(H2O)2]2+
Fe2+ : Fe(OH)2 - (react the same way as with sodium hydroxide)
Fe3+ : Fe(OH)3
Mn2+ : M(OH)2
Cr3+ : Cr(OH)3 dissolves in excess ammonia to form [Cr(NH3)6]3+
Colour changed with reduction of acidified Cr2O7(2-)
- Cr2O7(2-) is orange
- When acidified Cr2O7(2-) is added to zinc this produces Cr3+ which are green
- With an excess of zinc Cr3+ can be reduced further to Cr2+ which is a pale blue colour
Reduction of Cu2+ to Cu+ (by iodide)
When Cu2+ reacts with excess iodide ions, the Cu2+ forms a white ppt of copper(I) iodide and the iodine formed is brown.
Disproportionation of Cu+ ions (by sulphuric acid)
Cu2O(s) + H2SO4(aq) -> Cu(s) + CuSO4(aq) + H2O(l)
Brown ppt of copper and blue solution of copper sulfate. Cu+ has been oxidised and reduced
Reduction of Fe3+ to Fe2+ (by iodide)
2Fe3+ + 2I- –> 2Fe2+ + I2
When a solution of Fe3+ reacts with iodide ions, the Fe3+ ions are deduced to pale green Fe2+ but this is masked by the production of brown iodine
what is a -d block element?
elements with their highest energy electron I=in a -d sub-shell
they are metals, able to form complex ions
notes to remember for electron configuration of d block metals/ions
the 4S subs hell fills and empties before the 3d subs hell
electron configuration of chromium (doesn’t follow rules)
[Ar] 3d5 4s1
electron configuration of copper (doesn’t follow rules)
[Ar] 3d10 4s1
why don’t chromium and copper follow the usual rules of electron configuration?
stability.
It is believed that the half filled d5 sub-shell and the fully filled 610 sub-shell give additional stability to the atoms of chromium and copper.
what is a transition metal?
a d block element that forms at least one ion with a partially filled d orbital.
which d block elements are not classed as transition metals and why
zinc and scandium.
Zn 2+ and Sc 3+ do not have partially filled d orbitals.
properties of transition metals and their compounds
- form compounds where the transition metal can have different oxidation states
- form coloured compounds (different oxidation states have different colours)
- elements and compounds act as good catalysts
how to tell if a transition metal compound will be a good oxidising agent?
if the compound contains its transition metal in its highest oxidation state it is often a strong oxidising agent
iron colours (different oxidation states)
Fe +2 = pale green
Fe +3 = yellow
chromium colours (different oxidation states)
Cr +3 = green (acidified with sulfuric acid)
Cr +6 = orange (or yellow)
manganese colours (different oxidation states)
Mn +2 = very pale pink
Mn +7 = purple
examples of transition metals as heterogeneous catalysts
- MnO2 for decomposition of H2O2
- Fe for Haber process
when is a complex ion formed
a complex ion is formed when one or more ligand makes coordinate bonds to a central metal atom.
what is a ligand
a molecule or ion that donates a lone pair of electrons to a central metal ion to form a special kind of dative covalent bond called a coordinate bond
whats tells you how many coordinate bonds are being made with the central metal ion in a complex ion
the coordination number
representing complex ions
- whole ion enclosed in square brackets
- ligand inside round brackets
- overall charge outside brackets (charge of metal ion + any ligands)
eg [Cr(H2O)6] 3+
define a monodentate ligand
able to donate one pair of electrons to a central metal ion
common monodentate ligands
H2O, NH3, Cl-, Br-, CN-, OH-
define bidentate ligand
able to donate 2 lone pairs of electrons to a central metal atom.
conditions for a ligand to be multidentate
- contains two or more :N or :O atoms
- each :N or :O must be separated by at least 2 carbon atoms to allow enough stretch/bend to form two coordinate bonds at 90°
common bidentate ligands
1,2-diaminoethane (or en): H2:N-CH2-CH2-N:H2 ethanediote ion (oxalate ion): -::O(O)C-C(O)O::-
coordination number 6 - shape
octahedral
90° bond angle
coordination number 4 - shape
tetrahedral. 109.5° bond angle
EXCEPT complexes with platinum: square planar. 90° bond angle
coordination number 4 - shape
tetrahedral. 109.5° bond angle
EXCEPT complexes with platinum: square planar. 90° bond angle
cis-trans isomerism in a 4 bond complex ion
square planar (90° bond angle)
No more than 2 identical ligands eg [Pd(NH3)2Cl2]
Cis isomer - identical ligands are adjacent. 90° apart
Trans isomer - identical ligands are opposite. 180° apart
cis-trans isomerism in a 6 bond complex ion
octahedral shape (90° bond angle)
monodentate: 4 of one ligand and 2 of another eg [Co(NH3)4Cl2]+
bidentate: 2 identical ligands eg [Co(en)2Cl2]+
Cis isomer - identical ligands are adjacent. 90° apart
Trans isomer - identical ligands are opposite. 180° apart.
conditions for optical isomerism in complex ions
octahedral complexes only.
must contain 2 or 3 bidentate ligands.
Only cis isomers have optical isomers, trans isomers do not.
mirror images are non-superimposable
Examples of homogeneous catalysts?
- Reaction of iodide ions with S2O8(2-) catalysed by Fe2+
