Transition Metals

5.3.1 and 5.3.2

Transition element

Transition element

A metal that can form one or more stable ions with an incomplete d sub-level

Which d block elements are not transition elements?

Zn and Sc

Chemical properties of transition metals

• Form complex ions

• Variable oxidation states

• Coloured ions

• Catalysts

Complex ion

A central metal ion surrounded by ligands

Ligand

A molecule or ion that forms a dative covalent bond with a central metal ion by donating a pair of electrons

Dative covalent bond

A covalent bond where the shared pair of electrons have been donated by the same atom/molecule

Co-ordination number

The number of dative bonds to the central metal

Cations which form complex ions must have two feature....

1.they must have a high charge density, and thus be able to attract electrons from ligands. 2.they must have empty orbitals of low energy, so that they can accept the lone pair of electrons from the ligands.

Monodentate ligands

Ligands which donate pair of electrons to make a dative covalent bond to the central metal ion.

Bidentate ligands

Ligands which donate 2 lone pairs of electrons forming 2 coordinate bonds each.

Multidentate ligands

A molecule with forms more than 2 co-ordinate bonds

Co-ordination number of an octahedral

6

Co-ordination number of a tetrahedral

4

Chloride ions and other large ions form

Tetrahedral complexes with a coordination number of 4

Silver ions form

Linear complexes with a coordination number of 2

Which 2 ions form a square planar shape?

Platinum and Nickel

Stereoisomerism

A molecule with the same structural formula but its atoms are arranged differently in space

Optical isomer

These are non superimposable mirror images

Cis ligands

2 ligands are at 90o to each other

Trans ligands

2 ligands are at 180o to each other

Optical isomers occur with what shape of molecule?

Octahedral with 3 bidentate ligands

Ligand substitution

Where one ligand substitutes another.

Why can CO be deadly?

• CO can bind to haemoglobin sites, the same way oxygen can

• However, CO forms stronger dative covalent bonds

• The CO cannot be removed

• With CO, the stability constant is greater than with complex in O2

When monodentate ligands are replaced with bi/multidentate ligands, there is an increase in...

Entropy

Metal aqua ions

• Has 6 water ligands

• Octahedral shape

• Has the same charge as the metal (as water is neutral)

Cu2+ metal aqua ion colour

Blue solution

Co2+ metal aqua ion colour

Pink solution

Fe2+ metal aqua ion colour

Green solution (pale)

Fe3+ metal aqua ion colour

Yellow solution

Cr3+ metal aqua ion colour

Green solution

Mn2+ metal aqua ion colour

Pale pink solution

Cu2+ metal aqua ion with OH- colour

Blue precipitate

Co2+ metal aqua ion with OH- colour

Blue precipitate

Fe2+ metal aqua ion with OH- colour

Green precipitate

Mn2+ metal aqua ion with OH- colour

Brown precipitate

Cr3+ metal aqua ion with OH- colour

Green precipitate

Fe3+ metal aqua ion with OH- colour

Brown precipitate

Cu2+ metal aqua ion with NH3 colour

Blue precipitate

Co2+ metal aqua ion with NH3 colour

Blue precipitate

Fe2+ metal aqua ion with NH3 colour

Green precipitate

Mn2+ metal aqua ion with NH3 colour

Brown precipitate

Cr3+ metal aqua ion with NH3 colour

Green precipitate

Fe3+ metal aqua ion with excess NH3 colour

Brown precipitate

Cu2+ metal aqua ion with excess NH3 colour

Blue precipitate

Co2+ metal aqua ion with excess NH3 colour

Yellow/Brown solution

Cr3+ metal aqua ion with excess NH3 colour

Purple/Violet solution

Amphoteric

A molecule that is able to react both as a base and as an acid

Reaction with Chloride ions

• Co-ordination number of 4

• Tetrahedral

Oxidation of Iron (II)

Fe2+ can be oxidised to Fe3+ Usually use potassium manganate (VII)

Reduction of Iron (III)

Fe3+ can be reduced to Fe2+ Commonly use potassium iodide solution

Reduction of Chromium

(Cr2O7)2- can be reduced by Zn in acid solution Forms Cr3+ and Cr2+

True or False: It is easier to remove an electron from a negatively charged ion

True

Reduction of Cu2+

Cu2+ can be reduced to Cu+ using potassium iodide

Disproportionation of Copper (I) ions

Copper (I) ions will react with sulfuric acid to form Cu2+ and Cu metal

Testing for presence of a carbonate

• Add any dilute acid (ideally nitric acid)

• Observe for effervescence

Testing for presence of a sulphate

• Add BaCl2

• If present, white precipitate will form

Testing for presence of halide ions

• Add silver nitrate (AgNO3)

• Precipitates will form if present

• Chloride: white precipitate

• Bromide: cream precipitate

• Iodide: yellow precipitate

Silver chloride will dissolve in

Dilute ammonia

Silver bromide will dissolve in

Concentrated ammonia

Sequence of testing for negative ions

Carbonate, sulphate, halide

Test for ammonium ions

• React with warm NaOH

• Ammonia gas formed can be identified by turning red litmus paper blue