Mod 3- Transition Elements
- Created by: ava.scott
- Created on: 02-01-15 14:44
Transition Metals
A D-block element- An element with its highest energy level electrons in the d-subshell.
A Transition element- an element which creates ions with a partially filled d-subshell.
Scandium and Zinc are not transition elements, as their d-blocks are completely empty/full.
Chromium atoms:
A electron from the 4s subshell jumps up to the 3d subshell, to be more stable.
1s2,2s2,2p6,3s2,3p6,4s1,3d5
Copper:
A electron from the 4s subshell jumps up to the 3d subshell.
1s2,2s2,2p6,3s2,3p6,4s1,3d10
Properties of transition elements
Physical properties
- Shiny
- high density
- high MP and BP
- Exist in giant metal lattices
Chemical properties
- Variable oxidation states e.g. Fe2+/Fe3+
- Coloured compounds e.g. Cu2+ = blue
- Good catalysts NEXT PAGE
Catalysis and precipitation
Catalysts increase the rate of a chemical reaction by providing an alternative route for the reaction.
Transition metals provide a surface for the reaction to take place on. Reactants are adsorbed, and products desorbed.
Transition metals can change oxidation states, so can provide an intermediate for the reaction.
catalysed processes
Haber process-- to make AMMONIA for fertilisers
- uses an iron catalyst, whichmeans we can reduce temp to, and save energy.
- N2+ 3H2>>> 2NH3
Contact Process--- to make SULFURIC ACID for detergents, adhesives, explosives and batteries.
- Uses vandium oxide, where vanadium is oxidised to 5+.
- 2SO2 + O2 >>> 2SO3
Hydrogenation of alkenes to saturate them--
- uses NICKEL
- C2H4 + H2>> C2H6
decomposition of hydrogen peroxide-- for oxygen
- uses manganese (IV)oxide with managanese is 4+ state.
- H2O2 >>> 2H2O +O2
Aqueous ions and hydroxide ions
Cu2+
- [Cu(H2O)6]2+ + 2OH- >>> Cu(OH)2 +6H2O
- Light blue solution to blue ppt
Co2+
- [Co(H2O)6]2+ + 2OH- >>> Co(OH)2 + 6H2O
- pink solution to blue ppt (beige in oxygen)
Fe2+
- [Fe(H2O)6]2+ + 2OH- >>> Fe(OH)2 + 6H2O
- green solution to green ppt (red in oxygen)
Fe3+
- [Fe(H2O)6]3+ + 3OH- >>> Fe(OH)3 + 6H2O
- yellow solution to red ppt
Complex ions 4 definitions, common ligands
complex ion- a complex ion is a transition metal ion bonded to ligands by a coordinate bond.
ligand- a molecule which donates a lone pair to a central metal ion to make a coordinate bond.
coordinate bond- a bond where both electrons are donated by one molecule.
coordination number- this number represents the number of coordinate BONDS not the number of ligands.
common ligands e.g. water.
[Cu(H2O)6]2+
must have a lone pair.
charge must be shown outside the bracket
Shape of complex ion
shape of complex ions
- Most complex ions form a octahedral shape,
- with 6 bonds
- at 90 degrees.
CuCl42-
- Has a square planar shape
bidentate and multidentate
Bidentate
e.g. ethane-1,2-diamine. Both nitrogens act as ligands, and make coordinate bonds.
The nitrogen has a lone pair, which it can donate to make a coordinate bond.
2 bidentate and 2 monodentate --- can also show cis trans isomerism.
Hexadentate
e.g. EDTA u
- used in detergents- to bind with calcium and magneisum ions in water to reduce hardness
- in foods to remove metal ions that could oxidise the product
- added to blood samples to prevent clotting
- mercury poisoning cure.
Stereosisomerism
Optical isomers are non-superimposable mirror images of each other.
requirements
- a complex with three molecules or ions or a bidentate ligand
- a complex with two bidentate molecules and two monodentate
- one hexdentate molecule
cis-trans isomerism
e.g. with 2 bidentate and 2 monodentate molecules
CIS PLATIN
Anti cancer drug
- Two Cl groups, and two NH3 groups
it works by binding to DNA in cancer cells, and stopping division.
Precipitation
A precipitation reaction is when two soluble ions react to me an insoluble compound-- solid--ppt.
Transition metal ions react with aqueous NaOH to make coloured compounds.
e.g
Co2+ = pink solution
Co+ + OH- >>> Co(OH)2 = BLUE PPT
Fe2+ = green solution
Fe2+ + OH- >> Fe(OH)2 = GREEN PPT
Fe3+ = yellow solution
Fe3+ + OH_ >>> Fe(OH)3 = RED PPT
Ligand subsitution: Copper ions and ammonia
A ligand subsitution reaction is when the ligands in a complex solution are replaced by another.
Aqueous copper ions and ammonia
- Aqueous copper ions = BLUE solution
- Copper hydroxide = light blue ppt
- [Cu(NH3)4(H2O)2]2+= DEEP BLUE SOLUTION
[Cu(H2O)6]2+ + 4NH3 >>>> [Cu(NH3)4(H2O)2]2+ + 4H2O
Ligand subsitution: Copper/cobaltand HCL
Copper ions and concentrated hydrochloric acid
- aqueous copper ions= Pale blue solution
- copper chloride ions = green solution and then yellow.
It can be reversed by adding water.
The ligand complex formed is CuCl4(2-) from [Cu(H20)6]2+
Chloride ions are larger, so form a tetrahedral shape instead of octahedral.
Cobalt ions and hydrochloric acid
[Co(H2O)6]2+= a light pink solution
[CoCl4]2-= dark blue solution of
e.g. [Co(H2o)6]2+ + 4Cl- >>>> [CoCl4]2- + 6H2O
haemoglobin
Haemoglobin
Haemoglobin has non-protein haem groups and at the centre of each haem is a Fe2+ ion, which can bind to oxygen, allowing the protein to carry the molecule.
Fe2+ has four coordinate bonds to the nitrogens in the haem structure, one to the protein globin, and one for a oxygen molecule.
The iron can gain and release O2 freely.
Carbon monoxide
CO binds more strongly to the site on the Fe2+ molecules, and so stops oxygen from binding. This is a irreversible subsitution.
Will have a greater stability constant.
It is formed in the combustion in car engines, and also burning tobacco.
Kstab
Kstab is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions.
When ions are added to another set of ions, a concentration equilibrium is set up.
We can write a type of stability constant for this, called Kstab.
Cu2+ + 6H2O >>> [Cu(H2O)6]2+
You put products over reactants (always miss out water).
- put the mols to the power
A large kstab indicates the position of the equilibrium is to the right, and favours the products.
Complex ions often have a very high stability constant, and are easily formed.
REDOX REACTIONS
change in ox state x mols of oxidant = change in ox state x moles of reactant
MnO4- ions are colourless; Mn2+ ions are pink.
2Cu2+ + 4I- >> 2CuI + I2
MnO4(2-)+ 5e- +8H2O >>> Mn2+ + 4H2O
2S2O3(2-) + I2 >> 2I- + S4O6(2-)
Cr2O7(2-) + 6e- +14H+ >>>Cr3+ + 7H2O
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