MODULE 5: Transition Elements
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What are the unique features of the transition metals?
They act as catalysts, they have variable oxidation states, they form colourful compounds
What is the definition of a transition metal?
An element with one or more stable ions that have an incomplete d-orbital
What happens in the formation of ions in the transition metals?
The 4s orbital is depleted first as it is a higher energy level
What is the pattern of oxidation states in transition metals?
Increases across group up to manganese, then decreases.
For iron and chromium, what does the colour of their compound depend on?
Oxidation state
Give some examples of transition metals acting as heterogenous catalysts
Harber process (iron) and contact process (vanadium oxide (V))
What is a complex ion?
When a central metal ion is coordinately bonded to one or more ligand
What is a ligand?
A ligand is a compound with one or more active lone pairs that can form a coordinate bond
What is a coordination number?
The number of coordinate bonds a complex ion has
What are multidentate ligands?
A ligand with more than one active lone pair that can form 2 or more coordinate bonds.
What is the shape of a complex ion with 6 coordinate bonds?
Octahedral
What is the shape of a complex ion with 4 coordinate bonds?
Tetrahedral or square planar
What is the difference between tetrahedral and square planar structures?
Tetrahedral have a bond angle of 109.5, whereas square planar structures have bond angles of 90 (therefore are flat)
What complex ions are square planar?
Transition metals with 8 electrons in the highest energy d-sub-shell (gold, palladium and platinum)
What forms of isomerism occur in complex ions?
Cis-trans and optical
What is cis-trans isomerism in complex ions?
Cis = 90 degrees between ligands Trans = 180 degrees between ligands
What is optical isomerism in complex ions?
With multidentate ligands, when both molecules are cis but are non-superimposable over each other- they are mirror images of each other.
What is ligand substitution?
When one ligand in a complex ion is replaced with another one
What is the colour change when hexaaquacopper II ([Cu (OH2)6] (2+) is reacted with ammonia?
Pale blue solution to dark blue solution with a precipitate intermediate [Cu(H2O)6]2+ + 4NH3 –> [Cu(NH3)4(H2O)2]2+ + 4H2O
What is the colour change when hexaaquacopper II ([Cu (OH2)6] (2+) is reacted with chloride ions?
Pale blue to yellow solution with a green solution intermediate (change in shape to tetrahedral) [Cu(H2O)6]2+ + 4Cl- –> [CuCl4]2- + 6H2O
What is the colour change when hexaaquachromium III ([Cr (OH2)6] (3+) is reacted with ammonia?
Violet solution, grey-green precipitate intermediate, dissolves in excess to form purple solution [Cr(H2O)6]3+ + 6NH3 –> [Cr(NH3)6]3+ + 6H2O
What is the solution to precipitate colour change of Cu2+ with sodium hydroxide?
Blue solution to blue precipitate
What is the solution to precipitate colour change of Fe2+ with sodium hydroxide?
Pale green solution to green precipitate oxidises to Fe3+ when stood in air, so colour change to brown
What is the solution to precipitate colour change of Fe3+ with sodium hydroxide?
Pale yellow solution to orange-brown precipitate