Transition elements Module 5 Flashcards
Where are the transition elements found?
In the d block
Definition of a transistion element?
A d block element, that can form at least one stable ion with an incomplete d sub shell
So scandium and Zinc aren’t transition elements
Which transition elements are exceptions to the electron configuration filling up rules?
Chromium- prefers to have one electron in each orbital of the 3d subshell and just one in the 4s subshell, makes it more stable
Copper- prefers to have a full 3d subshell, and only one electron in the 4s subshell
When transition elements form ions, what shell are the electrons lost from first?
4s
Why scandium and Zinc aren’t transition elements?
Zn2+ only ion, which has a full d subshell
Sc3+ only ion, doesn’t have a d subshell
What is special about oxidation numbers in transition elements?
They can exist in variable oxidation states
Why are transistion elements good catalysts?
They can change oxidation states by losing or gaining electrons, within their d orbitals, so can transfer electrons to speed up reactions
Good at adsorbing substances onto their surfaces to lower the activation energy of reactions
3 examples of transition elements acting as catalysts?
CuSO4 catalyses the reaction of zinc with acids
MnO4 catalyses the decomposition of hydrogen peroxide
Iron is the catalyst in the haber process to produce ammonia
Pros and cons of catalysts?
Good for industry and the environment, as they allow reactions to happen faster, and at lower temperatures and pressures reducing energy usage
Can pose health risks as many of the metals and their compounds are toxic
Formula for when a transition element, is in aqueous solution?
{M(H2O)6)n+
What happens when you mix Copper(II) with NH3 (including equations)?
Cu2(+) + 2OH- = Cu(OH)2 goes from pale blue solution to a pale blue precipitate
OH is there as NH3 is a weak alkali
Then in excess NH3,Cu(OH)2 dissolves to form {Cu(NH3)4(H2O)2}2+ which is a dark blue colour
So the reaction is 4NH3 + {Cu(H20)6}2+ = (reversible) {Cu(NH3)4(H20)2}(2+) + 4H2O
What happens when you mix Iron(II) with NH3 (including equations)?
Fe(2+) + 2OH- = Fe(OH)2 pale green solution to a green precipitate, OH there as NH3 is a weak alkali
What happens when you mix Iron(III) with NH3 (including equations)?
Fe3+ + 3OH- = Fe(OH)3 goes from yellow solution to an orange precipitate, OH there as NH3 is a weak acid
What happens when you mix Manganese (II) with NH3 (including equations)?
Mn(2+) + 2OH- = Mn(OH)2 goes from pale pink solution to a light brown precipitate
What happens when you mix Chromium (III) with NH3 (including equations)?
Cr(3+) + 3OH- = Cr(OH)3 goes from a purple solution to a grey-green precipitate
Then in excess NH3, Cr(OH)3 dissolves to form {Cr(NH3)6}(3 +)which is a purple solution
So the equation is {Cr(H2O)6} + 6NH3 =(reversible) {Cr(NH3)6}(3+) + 6H20
What’s a complex ion?
A metal ion surrounded by coordinately (dative bond, both electrons are from the same atom) bonded ligands
What’s a ligand?
An atom, ion or molecule, that donates a pair of electrons to a central metal atom or ion
What’s the coordination number?
The number of coordinate bonds that are formed with the central metal atom (will either be 4 or 6)
What shape does 6 coordinate bonds form?
An octahedral shape, 90 degree bond angle
What shape does 4 coordinate bonds form?
Tetrahedral shape, 109.5 degree bond angle, or a square planar shape 90 degree bond angle
What must all ligands have?
A lone pair of electrons to be able to form the coordinate bond
1 lone pair = monodentate
2 lone pairs = bidentate, so can form 2 coordinate bonds with central atom
When can optical ismomerism occur in complex ions?
Occurs when an ion can exist in 2 non-superimposable mirror images (don’t match each other when put on top of each other)
So occurs when in octahedral complexes, when 3 biodentate ligands are attached to the central ion
How can cis-trans isomerism occur in complex ions?
When there’s only 2 different groups involved
The Cis isomers have the same groups on the same side (so are close together as they can be)
Trans have the same groups on opposite side
What is Cis platin?
A complex of platinum(II), with 2 chloride ions and 2 ammonia molecules in a square planar shape
How does Cis-Platin act as an anti cancer drug?
The 2 chloride ligands are very easy to displace. So the cis-platin displaces them, and bonds to 2 Nitrogen atoms on the DNA molecule, inside the cancerous cell instead
This block on it’s DNA prevents the cancerous cell from reproducing by division, causing the cell to die as unable to repair the damage
Why does Cis-platin need to be CIs and not Trans?
Needs the 2 chloride ions to be next to each other, in order to bind and work correctly
Downside of Cis-Platin as a cancer treatment?
Prevents normal cells from reproducing, including blood, so represses the immune system, increasing risk of infection
Can also damage the kidneys
In ligand subsitution what happens if the ligands are of similar size, eg H20, NH3 or CN-?
The ligands directly swap places, and the coordination number stays the same
(sometimes may be partial)
In ligand subsitution what happens if the ligands are of different sizes, eg H2O and Cl-?
There’s a change of coordination number and shape
How do you write a ligand substiution reaction?
Complex ion and reactant ligand on one side
Reversible reaction sign
New complex ion (coordination number, shape and charge may have changed) and the displaced ligand
Describe the Ligand substiution in haemoglobin?
Haemoglobin contains Fe2+ ions, which form 6 coordinate bonds, 4 of the lone pairs come from Nitrogen atoms, within a circular part of the molecule called haem, the fifth lone pair comes from a nitrogen atom binded to a protein (globin) The last one is a water ligand which attaches to the Iron
In the lungs there is high oxygen concentration, so the water ligand is substituted for an Oxygen molecule, forming oxyhaemoglbobin, this is then transported to respiring tissues where the oxygen is now dropped off and O2 concentration is low, so H2O binds back on
Can explain this reffering to le Chateillers principles and the reversible equation
What happens if CO is inhaled?
Water ligand is swapped for CO, forming a carboxyhaemoglobin, it’s a strong ligand so won’t readily exchange back with oxygen or water lingands, meaning haemoglobin can’t transport oxygen anymore
How do transition elements change oxidation number?
By gaining or losing electrons during a redox reaction
Describe the interconversion between Fe 2+ ions and Fe3+ ions?
Fe(2+) ions (pale green) are oxidised to Fe(3+) (yellow), by acidified potassium manganate solution
Fe(3+) ions (yellow) are reduced to Fe(2+) ions (pale green) by Iodide ions
Interconversion between Cr(3+) and Cr2O7(2-)?
Cr(3+) ion in (Cr(OH)6)3- (dark green) is oxidised to the yellow CrO4(2-) by warming with hydrogen peroxide solution in alkaline conditions
Then dilute sulfuric acid is added to CrO4(2-) to produce the orange Cr2O7(2-)
Cr2O7(2-) (orange) is reduced to Cr3+ (green) by acidified zinc
Interconversion between Cu2+ and Cu+?
Cu(2+) (pale blue) is reduced to the off-white precipitate Copper iodide by iodide ions
Cu(+) spontaneously disproportionates into to produce Cu and Cu(2+)
What colour precipitate is formed, when NaOH is reacted with the transistion Ion Cu(2+)?
blue
What colour precipitate is formed, when NaOH is reacted with the transistion Ion Fe(2+)?
green
What colour precipitate is formed, when NaOH is reacted with the transistion Ion Fe(3+)?
Orange
What colour precipitate is formed, when NaOH is reacted with the transistion Ion Mn(2+)?
Light brown
What colour precipitate is formed, when NaOH is reacted with the transistion Ion Cr(3+)?
Grey/green
How do you test for a carbonate ligand?
Add Nitric acid to the test compound, and bubble any gas given off through limewater
Limewater will go cloudy if present, as CO2 produced
How do you test for a chloride ligand?
Add silver nitrate to the compound
White precipitate formed if present
How do you test for a bromide ligand?
Add silver nitrate to the compound
Cream precipitate forms if present
How do you test for an Iodide ligand?
Add silver nitrate to the compound
Yellow precipitate forms if present
How do you test for Sulphate ligand?
Add Barium Nitrate or Barium Chloride, white precipitate will form if present
How do you test for an ammonium ligand?
Add cold NaOH to the test compound and warm, hold damp, red litmus paper over the solution
Red litmus paper will turn blue in presence of ammonia
How do you get [Cr(OH)6]?
React Cr(OH)3 with NaOH
How do you get {Cu(Cl)4}2-?
{Cu(H2O)6}(2+) + 4Cl- =(reversible) {Cu(Cl)4}(2-) + 6H2O
