Chapter 24 Transition Elements Flashcards
What are the D block elements?
Elements found between group 2 and group (1)3
Highest energy electron found in a d orbital
What are the electron configurations of chromium and copper?
Cr= …3d5 4s1
Cu= 3d10 4s1
Half or full d sub shell more stable than not, and so electron excites from the 4s orbtial
Which orbital for d block elements is removed first?
4s
It’s why a lot of d block elements have 2+ ions
Filling 4s first, also empties first as the energy of the 3d falls below that of the 4s when both are filled
What is the definition for transition metals? What D block elements do not count as transition metals?
D block elements that form at least 1 ion with a partially full d-orbital
Zinc - only Zn2+ so a full d sub shell
Sc- not Sc3+, so an empty d sub shell
What are the colours of chromium in various oxidation states?
Cr2+ = light blue
Cr3+ = dark Green
Cr4+ and Cr5+ = colourless
Cr6+ = orange or yellow
What is the link between oxidation state and oxidising potential?
Transition metals in high oxidation states are good oxidising agents as the metal complex wants to be reduced
E.g MnO4- +7 wants to be Mn2+
What are some examples of transition metals as catalysts?
Haber Process- N2 + 3H2 —/2NH3. Catalysed by Fe
Contact Process- 2SO2 + O2 —/2SO3 Catalysed by V2O5
Iodide-peroxydisulphate- catalyses by Fe2+
What is a complex ion?
Central metal ion with one or more ligands bound to it by dative covalent bonds
What is a ligand?
A molecule or ion that donates a one pair of electrons to a central metal ion via dative covalent bonding
How do you write a complex ion?
Square brackets around the whole complex
Round brackets for the ligands
Charge on the outside
E.g [Cr(NH3)6] 3+
What is a coordination number?
The number of dative covalent bonds made to a central metal ion in a complex ion
What is the shape of a complex with a coordination number of 6? What about 4?
6-Octahedral
4- usually tetrahedral
But if 8 d electron in the ion, becomes square planar
Usually Pt, Au(III) Pd
What is a monodentate ligand? What is a bidentate ligand?
A ligand which is able to donate 1 lone pair of electrons to a central metal ion, forming 1 coordinate bond e.g ammonia
A ligand which is able to donate 2 lone pairs of electrons to a central metal ion via dative covalent bonding e.g ethanedioate
When and how is stereoisomerism present in 4 coordinate complexes?
When there no more than 2 identical ligands
Cis/Trans
Same side= Cis, 90 degrees
Opposite side= trans, 180 degrees
When does Cis/Trans isomerism occur in 6 coordinate complexes?
When two identical ligands and 2 bidentate ligands
Or 4 identical and 2 different
Same monodentate = 90 degrees, Cis
Opposite monodentate= 180 degrees, Trans
Why do some 6 coordinate complexes have optical isomerism and which do?
Mirror images are not superimposable
In Cis 2 bidentate and 2 monodentate
And 3 bidentate
Draw the mirror image
What is Cis-platin and how does Cis-platin work?
[Pt(NH3)2Cl2]
Anti-cancer drug which inhibits cell division, shrink tumour sizes but lots of side effects
Forms a complex with guanine where the Cls are substituted by the nitrogen’s in the base, prevents DNA replication and triggers apoptosis
What is ligand exchange?
When one ligand is swapped for another
What happens when chromium reacts with dropwise then excess ammonia
Originally Cr3+ Violet
Dropwise- base, hydroxide
Cr3+ + 3OH- —/ Cr(OH)3 (s). Grey green
Excess, full substitution
Cr(OH)3 + 6NH3 —/ [Cr(NH3)6]3+ + 3 OH- Purple
What happens if chromium hydroxide is reacted with excess NaOH?
Grey-Green to Dark Green
Cr(OH)3 + 3OH- —/ [Cr(OH)6]3-
What happens with Cu2+ reacts with dropwise then excess ammonia?
[Cu(H2O)6]2+ pale blue
Dropwise Cu(H2O)6 + 2OH- —/ Cu(OH)2(H2O)4 + 2H2O Blue precipitate
Excess Cu(OH)2(H2O)4 + 4 NH3 —/ [Cu(H2O)2(NH3)4]2+ + 2OH- + 2H2O. Dark Blue solution
Pale blue solution, then blue precipitate, then dark blue solution, partial substitution
What happens when Cu2+ reacts with HCl? Why?
[Cu(H2O)6]2+ + 4Cl- —/ [CuCl4]2- + 6H2O
Pale blue to Yellow
Change in coordination number as the chloride ligands are larger than water, physically not enough space for 6 of them
Why does adding acid enable transition metal hydroxides to dissolve?
Fe2+ + 2OH- /=/ Fe(OH)2
Reversible reaction, adding acid decreases the concentration of hydroxide
Pushes the position of equilibrium to the left, so more ions less precipitate
What is the colour of Fe2+ in solution and it’s hydroxide? Is it soluble in excess hydroxide?
Pale Green solution
Green precipitate
Insoluble
What is the colour of Fe3+ in solution and it’s hydroxide? Is it soluble in excess hydroxide?
Pale yellow solution
Orange/brown precipitate
Insoluble
What is the colour of Mn2+ in solution and it’s hydroxide? Is it soluble in excess hydroxide?
Pale pink solution
Light brown precipitate
Insoluble
What is the structure of Haemoglobin?
Metalloprotein
Fe2+ with a multidentate haem group coordinated to it
1 space of the globulin protein, and the other for oxygen to coordinate to
What is the function of Haemoglobin? Why is CO toxic?
To transport oxygen around the body
Coordination of oxygen creates a weak dative covalent bond, this is a reversible reaction and O2 can disassociate where it is needed by cells for respiration
The C of CO forms a much stronger dative covalent bond, substituting for the oxygen, and this is permanent
Oxygen can no longer be transported around the body so cells cannot respire, leading to cell death
How do you convert between Fe2+ and Fe3+ including colour changes?
Fe2+= Green Fe3+= orange brown
To produce Fe3+, adding an oxidising agent to Fe2+ such as H+/MnO4-
To produce Fe2+, adding a reducing agent to Fe3+ such as I-
How do convert between Cr3+ and Cr2O7 2- including colours and intermediates?
Cr3+=Green Cr2O72-= Orange
Oxidise Cr3+ by reacting with H2O2/OH-, first forming yellow CrO4 2-, then Cr2O7 2-
Reduce Cr2O7 2- with Zn/H+, with excess reducing to form Cr2+ blue
What is the reaction between Cu2+ and Iodide?
2Cu2+ + 4I- —/ 2CuI + I2
White solid and brown solution
What is the reaction between hot Sulphuric acid and Cu2O?
Cu2O+ H2SO4 —/ Cu + CuSO4 + H2O
Brown solid and blue solution
What pH is better for reduction and oxidation?
Reduction= acidic
Oxidation = alkaline
Think about oxidation is the loss of hydrogen and bases remove hydrogens
What shape molecules goes silver form as a complex ion?
Linear, only two ligands
How do transition metals catalyse reactions when homogeneous?
Relies on the variable oxidation states of transition metal ions
The ion will take the electron from one molecule and reduce itself
It will then oxidise itself by giving the electron to the other reaction
Thus catalysing the reaction and regenerating the catalyst
Needs an electrode potential between the two reactants
