Chapter 24 - Transition Elements Flashcards
What is the electronic configuration of Chromium
1S2 2S2 2P6 3S2 3P6 3D5 4S1
What is the electronic configuration of Copper
1S2 2S2 2P6 3S2 3P6 3D10 4S1
Why do copper and chromium have weird electronic config.s?
Because it is more stable to have half or full of the 3D subshell rather than have nearly half or nearly full of 3D subshell.
Define a transition element
They form at least 1 ion with a partially filled d-orbital.
What elements seem like they would be transition metals elements, but aren’t?
Scandium and zinc.
Because scandium only forms a 3+ ion, and it had no electrons in the 3d subshell.
Because zinc only forms a 2+ ion, meaning that it has a full 3D10 shell, which isn’t partially filled.
Properties of Transition metals
Different oxidation states
Colourful compounds
Can be used as catalyst.
Why do they form colourful compounds?
The 3D shell can split and when electrons move between 2 split 3 shells, they often give off colours from the EM spectrum.
Why do transition metals form good catalysts?
Because they can form many oxidation states , hence they can easily lend and take electrons from other substances.
Main examples of the transition metals acting as catalysts
Iron for the Harbour process
Vanadium oxide (V2O5) for the contact process.
Nickel for hydrogenation.
MnO2 - decomposition of hydrogen peroxide to water and oxygen.
What is a heterogenous catalyst?
Different phase to the reactants.
What is a homogenous catalyst?
Same phase as the reactants.
What is a ligand?
A molecule or an ion that forms a coordinate bond with a transition metal by donating a pair of electrons.
What is a coordinate bond?
A type of covalent bond where both the electrons are from the same atom.
What is a coordination number?
The number of coordinate bonds on the central metal atom or ion.
What are the types of ligands?
Monodentate
Bidentate
Multidentate
Monodentate ligands
they form a single coordinate bond. like H20, NH3, and Cl-
Bidentate ligands
They form 2 coordinate bonds, like C204 2-
Multidentate ligands
They form many coordinate bonds. Like EDTA4- which forms 6 coordinate bonds.
Explain what happens when water and ammonia react?
When they react with transition metals, the water molecules are attracted to the positive metal ions. Because transition metals have a high charge density, they can easily attract ligands.
Why do Complexes with chlorine only have 4 coordinate bonds, but those with water have 6?
Because Chlorine is generally bigger than water molecules, so only 4 can fit.
What is usually the shape of small monodentate ligands?
Coordinate number of 6 , shape: octahedral
What is usually the shape of large monodentate ligands?
Coordinate number: 4 ,
shape: tetrahedral/ square planar
What is the Tollen’s Reagant
[H3N-Ag-NH3] +
What is stereoisomerism?
They have the same structural formula, but different spacial arrangement of atoms.
What are the 2 types of stereoisomerism?
Optical and cis-trans
Where does cis-trans occur?
square planars and octahedrals
What is a cis- isomer in this?
2 identical groups are adjacent to each other and have a bond angle of 90 degrees
What is trans- isomer?
2 identical rgoups are opposite to each other and have a bond angle of 180
What colour is cis- [co(NH3)4(Cl)2]+
violet
What colour is trans- [co(NH3)4(Cl)2]+
Green
Roles in medicine of cis-platin
It was found that cis-platin can be used to attack tumour but it has a bad side effect to the kidneys. It works by forming a platinum complex inside a cell which binds to DNA and prevents the DNA replicating. If this is applied to a healthy cells it lead to cell death.
Where does optical isomerism work?
In octahedral complexes, containing 2 or more bidentate ligands, and only is cis- isomers.
What is optical isomerism?
They are mirror images of each other, called non-superimposable.
What is a ligand substitution reaction?
When one ligand is replace by another.
What is a precipitation reaction?
When 2 aqueous solutions react together to form an insoluble ionic solid known as precipitate.
What is the colour of aqueous copper(II) solution ?
Pale blue solution.
If you add a small amount of ammonia to aqueous copper(II) solution, what happens?
The ammonia acts as a base, creating Cu(Oh)2(H20)4 and 2NH4+
This is a blue solid
If you add an excess of ammonia to aqueous copper(II) solution, what happens?
The precipitate dissolves and the ammonia replaces the water.
Equation for Excess ammonia and aqueous copper(II) solution
cu(OH)2(H20)4 + 4NH3(aq) [Cu(NH3)4(H20)2]4+ (aq) + 2H20 + 2OH-
Final equation for ammonia and aqueous copper(II) solution
[Cu(H20)6]2+ + 4NH3(aq) –> [Cu(NH3)4(H20)2]2+ +4H20
Starts off as pale blue.
Ends as dark blue.
Equation of little ammonia and aqueous copper(II) solution
[Cu(H20)6]2+ + 2OH—> Cu(OH)2 (s) + 6H20
Then
Cu(OH)2 +2H2O + 4NH3 –> [cu(NH3)4(H20)2]2+ +2OH-
Equation for aqueous copper(II) ions and HCl
[Cr(H20)6]2+ + 4Cl-
[CuCl4]2- + 6H20.
Colours for aqueous copper(II) ions and HCl
aqueous copper(II) ions is pale blue and HCl is yellow. The solution may actually end up looking greenish due to the blue and yellow mixing.
Equation for aqueous chromium(III) ions and NH3
[Cr(H20)6]3+ +6NH3 —> [Cr(Nh3)6]3+ + 6H20
[Cr(H20)6]3+ is grey-green
[Cr(Nh3)6]3+ is dark green.
Equation for aqueous chromium(III) ions and little bit of NH3
[Cr(H20)6]3+ + 3NH3 –> Cr(H20)3(Oh)3 +3NH4+
Goes from pale purple to a green solid.
Equation for aqueous chromium(III) ions and an excess of NH3
Cr(H20)3(Oh)3 + 6NH3 [Cu(NH3)6]3+ +3H20 + 3OH-.
Ligand substitution in our blood
Each haem group has a Fe+ ion.
O2 can bind to the Fe+ and then release when the O2 binds to the haem group.
Cu2+ + OH
Cu2+ + 2OH –> C(OH)2 (s)
A blue precipitate.
It is insoluble in excess NaOH
Fe2+ +2OH-
Fe2+ +2OH- –> Fe(OH)2
A green precipitate
Insoluble in excess NaOH, but it is oxidised in air.
Fe(OH)3
An orange precipitate.
Fe3+ + 3OH-
Yellow solution to an orange precipitate.
Insoluble in excess NaOH.
Mn2+ + 2OH-
Mn2+ + 2OH- –>Mn(OH)2(s)
Pale pink to a light brown precipitate
Insoluble in excess NaOH.
Cr3+ +3OH-
Cr3+ +3OH- –> Cr(OH)3
Green precipitate
Cr(OH)3 + 3OH-
Cr(OH)3 + 3OH- –> [Cr(OH)6]3-
A dark green solution.
Cu2+ + 2OH-
Cu2+ + 2OH- –> Cu(OH)2
A blue precipitate
What is a cells’ Standard Electrode Potential (or E sigma)
A potential difference that is created between ex. Cu and Cu2+ due to the movement of electrons.
symbol: E°
In a beaker with Cu2+ ions in a solution and Cu stick, what is the reaction
Cu Cu2+ + 2e-
How can 2 half cells be put together to create a full cell?
Put a voltmeter connecting the 2 sticks and a “salt bridge” between the 2 beakers. This can be filter paper soaked in a very saturated solution such as potassium nitrate.
How do you figure out which reaction is redox and which is oxidation?
Look at the E°.
Whichever one has the more positive one, then reduction will happen there.
Reduction will only happen at the +ve terminal.
How to write the initial reaction for a full cell
Figure out which cell is +ve and -ve.
Then, write the redox and oxidation reactions.
Then, cancel and balance the electrons.
What colour is Fe3+
orangey-brown
What colour is 2I-
colourless
What colour is Fe 2+
Pale green
What colour is MnO4 -
Purple
What colour is Cr3+
green
What colour is Cr2072-
Orange
What colour is Cr2+
pale blue
What colour is Cu2+
pale blue
What colour is CuI
white precipitate
What colour is Cu
Brown solid
