Transition element definition
A d-block element that can form at least one ion with an incomplete d sub-shell.
Why aren’t scandium and zinc transition elements
-Scandium only forms one stable ion Sc3+ which has an empty d sub-shell.
-Zinc only forms Zn2+ ions which have a full d sub-shell.
So neither form ions with incomplete d sub-shell.
Properties of transition elements
-Can form coloured compounds.
-Have more than one oxidation state for each element in its compounds.
-Transition elements and their compounds can be used as catalysts due to variable oxidation states meaning they can facilitate electron transfer between reactants.
Benefits of catalysts and risk
-Increase rate of reaction at lower temps and pressures, reducing energy usage and cost which benefits industry and the environment.
-Potential health risks as many are toxic.
Examples of transition elements as catalysts
-MnO2 catalyses decomposition of hydrogen peroxide.
-Cu+ ions catalyse reaction of zinc with acids.
Complex ion definition
Metal ion surrounded by co-ordinately bonded ligands.
Ligand definition
An atom, ion or molecule which can donate a lone electron pair to a central metal ion to form a coordinate/dative covalent bond.
Examples of monodentate ligands
H2O
Cl–
NH3
Bidentate ligand example
NH2CH2CH2NH2 (1,2-diaminoethane also known as ‘en’)
Coordination number
The number of coordinate bonds attached to central ion
Octahedral complex ion examples
Many hexaaqua complexes:
-[Cu(H2O)6] 2+
-[Fe(H2O)6] 3+
Tetrahedral complex ion examples
Many tetrachloro complexes:
-CuCl4 2–
-CoCl4 2–
Square planar complex ion examples
Complexes of Pt, e.g. platin:
-Pt(NH3)2Cl2
Things that should be included when drawing complex ions
-Arrow heads to show dative covalent bonds.
-Lone pairs
-Arrows coming from specific atom of ligand that has lone pair.
How to identify cis or trans isomerism in octahedral and planar complexes
-Cis isomers have identical ligands next to each other with a bond angle of 90 degrees between them.
-Trans isomers have identical ligands opposite each other with a bond angle of 180 degrees between them.
Describe the structure of cis-platin
Square planar complex with two Cl- ligands and two NH3 ligands coordinately bonded to platinum (ll) with the same ligands next to each other.
When does optical isomerism occur?
Occurs in octahedral complexes containing 2 or more bidentate ligands.
(A type of stereoisomerism)
How is cis-platin used as an anti-cancer drug?
Used in chemotherapy by displacing chloride ligands and forming coordinate bonds with nitrogen atoms on DNA molecules in the cancerous cell, preventing the cancer cell from replicating.
Transition element ions in solution exist as ……
Hexaaqua complex ions (has six water ligands attached to it).
For example Cu2+(aq) is [Cu(H2O)6]2+(aq)
Cu2+ ions in water
Light blue solution of [Cu(H2O)6]2+(aq)
Reaction of [Cu(H2O)6]2+(aq) with concentrated HCl (aq)
-Forms yellow solution of [CuCl4]2-
as water ligands displaced by chloride ligands.
-Tetrahedral complex with coordination number of 4 formed as chloride ligands bigger than water ligands.
What happens if water is added to [CuCl4]2- (aq)
Water ligands displace chloride ligands as reversible reaction. Light blue solution of [Cu(H2O)6]2+(aq) is reformed but paler due to being more dilute from added water.
Why might the solution turn green in the reaction between [Cu(H2O)6]2+(aq) and conc HCl (aq)
As yellow solution of [CuCl4]2- is formed from blue solution of [Cu(H2O)6]2+(aq), both coloured solutions can mix forming a green solution.
Reaction between [Cu(H2O)6]2+(aq) and dropwise NH3(aq) or dropwise NaOH(aq)
-Light blue precipitate of Cu(OH)2(s) / Cu(OH)2(H2O)4 (s) is formed.
-This is due to NH3 and NaOH being bases so accepting H+ ions from H2O.
No square brackets for precipitates.
Cu(OH)2(s) = Cu(OH)2(H2O)4 (s)
