Mod 3- Transition Elements

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  • 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

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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
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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.

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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
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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
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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

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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
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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.
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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.

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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

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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

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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

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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.

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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.

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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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