3.4 D-block Flashcards
What is a transition metal?
Element that possesses a partially filled d sub-shell as an atom or in its stable ions
Can d-block transition metals attain various oxidation states in their compounds?
Yes
How can d-block transition metals attain various oxidation states in their compounds?
The energy levels of the 4s and 3d sub-levels are very close which means different numbers of electrons can be gained or lost using similar amounts of energy
Common oxidation states of chromium
+3
+6
Common oxidation states of manganese
+2
+4
+7
Common oxidation states of iron
+2
+3
Common oxidation states of cobalt
+2
+3
Common oxidation states of copper
+1
+2
Colour of aqueous solutions of compounds containing Cr3+
Green
Colour of aqueous solution of compounds containing CrO4^2-
Yellow
Colour of aqueous solution of compounds containing Cr2O7^2-
Orange
Colour of aqueous solution of compounds containing MnO4^-
Purple
Colour of aqueous solution of compounds containing Co^2+
Pink
Colour of aqueous solution of compounds containing Fe^2+
Pale green
Colour of aqueous solution of compounds containing Fe^3+
Red-brown
Colour of aqueous solution of compounds containing Cu^2+
Pale blue
What is a ligand?
Small molecule or ion with a lone pair of electrons which can bond to a transition metal ion
How many ligands does a tetrahedral transition metal complex have?
What angle are these to eachother?
4
109.5 degrees
How many ligands does a octahedral transition metal complex have?
What angle are these to eachother?
6
90 degrees
Is a tetrahedral or octahedral transition metal complex more common?
Octahedral
When is a transition metal ion coloured
In complexes
What energy do d-orbitals in a transition metal ion have when there is no ligand?
Degenerate
The same
What happens to the energy levels of d-orbitals of transition metals when a ligand approaches?
Energy of 3 of the d-orbitals become different to the other 2
3 of lower energy
2 of higher energy
How does an electron in one of the d-orbitals move between the sets of orbitals of different energies?
It needs to gain sufficient energy which is absorbed in the form of light
How many frequencies of light is absorbed as an electron gains energy in a d-orbital and why?
1
It corresponds to the energy gap between orbitals
Which colour is seen after light is absorbed by an electron from a d-orbital?
The complementary colour is reflected
The colour seen is made up of the light frequencies that are NOT absorbed
Colour of compounds containing ((Cu(H2O)6))^2+ and which region of the spectrum is absorbed
Pale blue
Light in red region is absorbed
Colour of complexes containing ((Fe(H2O)6))^3+ and which region of the spectrum is absorbed
Yellow
Light in the purple region is absorbed
Are all transition metal complexes coloured and why?
No
Electrons cannot move from lower to higher orbitals as they either have a full d sub-shell or an empty d-subshell
Examples of colourless transition metal complexes
Copper(I) - full d sub-shell
Scandium(III) - empty d sub-shell
What is a ligand exchange reaction
Where a ligand in a complex ion is replaced by a different one
Why is concentrated hydrochloric acid used in ligand exchange reactions?
Provides a high concentration of chloride ions
Why can less chloride ions fit around a complex ion than other ligands eg water molecules
Chloride ions are bigger than water molecules so there isn’t room to fit six around the central metal ion
What happens if conc HCl is added to a solution containing ((Cu(H2O)6))^2+
6 water molecules are replaced by 4 chloride ions
What happens if conc HCl is added to a solution containing ((Co(H2O)6))^2+
6 water molecules are replaced by 4 chloride ions
Colour of ((Cu(H2O)6))^2+
Blue
Colour of ((Cu(NH3)4(H2O)2))^2+
Royal blue
Colour of ((Co(H2O)6))^2+
Pink
Colour of ((CuCl4))^2-
Yellow-green
Colour of ((CoCl4))^2-
Blue
Homogenous transition metal catalysts
• same physical state as reactants
• use variable oxidation states to oxidise/reduce a reactant
• transition metal is returned to original oxidation state by a reaction with another molecule
Examples of homogeneous transition metal catalysts
• Manganese(IV) oxide in decomposition of hydrogen peroxide
• Vanadium(V) oxide in the contact process, conversion of SO2 to SO3, vanadium(V) oxide is reduced from +5 to +4 and then reformed to original oxidation state
Heterogenous transition metal catalyst
• different physical state to the reactants
• partially filled d-orbitals
• provides a solid surface for reactants to be adsorbed and brought closer for more opportunity to react
• molecules with lone pair of electrons can form coordinate bonds to the metal as there are available empty d-orbitals, this increases reactivity of species bonded to the metal
Examples of heterogenous transition metal catalysts
• iron - Haber process
• nickel - hydrogenation of vegetable oil to form margarine
What happens when NaOH(aq) is added to most transition metal ions
A coloured precipitate forma
What does it mean if the precipitate of a transition metal ion dissolves on addition of excess NaOH(aq)
The transition metal is atmophoteric
Cr3+ Solution colour
Observation after OH- is added
Observation after excess OH- is added
Green
Grey-green precipitate
Precipitate dissolves giving a deep green solution
Fe2+ Solution colour
Observation after OH- is added
Observation after excess OH- is added
Pale green
Dark green precipitate
No change
Fe3+ Solution colour
Observation after OH- is added
Observation after excess OH- is added
Yellow
Red-brown precipitate
No change
Cu2+ Solution colour
Observation after OH- is added
Observation after excess OH- is added
Pale blue
Pale blue precipitate
No change
Ionic equation when NaOH(aq) is added to a solution containing Cr3+
Cr3+(aq) + 3OH-(aq) —> Cr(OH)3(s)
Cr(OH)3(s) + 3OH-(aq) —> [Cr(OH)6]3-(aq)
Ionic equation when NaOH(aq) is added to a solution containing Fe2+
Fe2+(aq) + 2OH-(aq) —> Fe(OH)2(s)
Ionic equation when NaOH(aq) is added to a solution containing Fe3+
Fe3+(aq) + 3OH-(aq) —> Fe(OH)3(s)
Ionic equation when NaOH(aq) is added to a solution containing Cu2+
Cu2+(aq) + 2OH-(aq) —> Cu(OH)2(s)
