Chapter 24 - Transition Elements Flashcards
What are the 2 exceptions in electron configuration of d-block elements?
Chromium - 3d5 4s1 is more stable than 3d4 4s2
Copper - 3d10 4s1 is more stable than 3d9 4s2
Define transition elements.
D-block elements that can form at least one ion and have a partially filled d-orbital
Which d-block elements are not considered transition elements and why?
Scandium - Only forms the ion Sc3+ by loss of two 4s electrons and one 3d electron, causing it to have an empty d-orbital.
Zinc - Only forms Zn2+ ion by losing two 4s electrons, causing it to have a full d-orbital.
What are the properties of transition elements?
They form compounds that can have different oxidation states.
They form coloured compounds
Elements and compounds can act as catalysts.
What are the colours of Chromium ions?
3+ is green
6+ is orange
What colour are copper ions?
2+ is blue
What colour is Potassium Dichromate (VI), K2Cr2O7?
Orange
What colour is Cobalt (II) Chloride, CoCl2?
Pink-purple
What colour is Nickel (II) Sulphate, NiSO4?
Green
What colour is Hydrated Copper (II) Sulphate, CuSO4xH2O?
Blue
What are the colours of Iron ions?
2+ is pale green
3+ is yellow
What catalyst is used in the Haber process?
Iron
What catalyst is used in the Contact process?
Vanadium (V) Oxide, V205
What catalyst is used in Hydrogenation?
Nickel
What catalyst is used in catalytic decomposition of hydrogen peroxide?
Manganese (IV) Oxide, MnO2
Define what a coordinate bond is (Dative covalent bond).
A type of covalent bond in which one of the bonded atoms provides both electrons for the shared pair.
Define what a ligand is.
A molecule or ion that donates a pair of electrons to a central metal ion to form a dative covalent bond.
Define what a complex ion is.
A transition metal ion bonded to ligands by dative covalent bonds.
What is meant by a monodentate ligand?
A ligand that only donates one pair of electrons to the central metal ion.
What is meant by a bidentate ligand?
A ligand that donates two pairs of electrons to the central metal ion.
Give 5 examples of common monodentate ligands and their charges.
Water, H2O = 0 Ammonia, NH3 = 0 Cyanide, CN = -1 Chloride, Cl = -1 Hydroxide, OH = -1
What is a coordination number?
The number of coordinate bonds attached to the central metal ion.
What shape is created from a complex ion having a coordination number of 6?
Octahedral
What shapes can be created from a complex ion having a coordination number of 4?
Tetrahedral
Square Planar
What bond angle do octahedral shapes have?
90 degrees
What bond angle do tetrahedral shapes have?
109.5 degrees
What bond angle do square planar shapes have?
90 degrees
When is a square planar shape formed in a complex ion? Give 3 examples.
When the transition metal has 8 d-electrons in the highest energy d-subshell.
Platinum (II), Pt2+
Palladium (II), Pd2+
Gold (III), Au3+
What is stereoisomerism?
Same structural formula but a different arrangement of atoms in space.
What are the 2 types of stereoisomers?
Cis-trans isomerism
Optical isomerism
When can complex ions show cis-trans isomerism?
4- or 6-coordinate complex ions with 2 different monodentate ligands
When can complex ions show both types of stereoisomerism?
6-coordinate complex ions containing monodentate and bidentate ligands.
What is optical isomerism?
Molecules are non-superimposable images of each other.
Called enantiomers.
Define ligand substitution.
One ligand in a complex is replaced by another ligand.
Describe ligand substitution of aqueous copper (II) ions with ammonia.
4 of the Waters (H2Os) are replaced by ammonia ligands (NH3), the solution goes from pale blue to dark blue.
Describe ligand substitution of aqueous copper (II) ions with chloride ions.
The 6 Water (H2O) ligands are replaced by 4 chloride ion (Cl-) ligands. Solution goes from pale blue to yellow.
Why does the shape change from octahedral to tetrahedral in ligand substitution of aqueous copper (II) ions with chloride ions?
Because chlorine ligands are larger than water ligands, so fewer chloride ligands can fit around the central Cu2+ ion.
Why does the solution of aqueous copper (II) ions reacting with chloride ions turn green as the reaction progresses?
The yellow and blue solutions mixing gives a green colour
What is formed when Chromium (III) Potassium Sulphate, KCr(SO4)2, is dissolved in water? And what colour is the solution?
The complex ion [Cr(H2O)6]3+ is formed, a pale purple solution.
What is formed when only Chromium (III) Sulphate is dissolved in water? And what colour is the solution?
The complex ion [Cr(H2O)5SO4]+ is formed, a green solution.
Describe the reaction between [Cr(H2O)6]3+ and an excess of aqueous ammonia and name the colour of the solution.
A grey-green precipitate of Cr(OH)3 is formed initially.
Cr(OH)3 dissolves in excess ammonia to form the complex ion [Cr(NH3)6]3+.
It is a purple solution.
How does ligand substitution help with gas exchange in blood?
In haemoglobin, there is a central Fe2+ ion that can bind to oxygen gas.
The oxygen is released into cells and then CO2 can bind to the Fe2+ ion where it is released in the lungs.
What is a precipitation reaction?
2 aqueous solutions containing ions react together to form an insoluble ionic solid.
Describe the precipitation reaction of Cu2+ with NaOH.
Blue solution reacts to form a blue precipitate of copper (II) hydroxide, Cu(OH)2
Precipitate is insoluble in excess sodium hydroxide.
How do Fe2+, Fe3+, and Mn2+ react with an excess of aqueous ammonia?
The same way that they react with NaOH.
They form hydroxide precipitates that are insoluble in excess ammonia.
Describe the precipitation reaction of Fe2+ with NaOH.
Pale green solution reacts to form a green precipitate of iron (II) hydroxide, Fe(OH)2
Precipitate is insoluble in excess sodium hydroxide but turns brown in air as it is oxidised to iron (III) hydroxide.
Describe the precipitation reaction of Fe3+ with NaOH.
Pale yellow solution reacts to form a brown precipitate of iron (III) hydroxide, Fe(OH)3
Precipitate is insoluble in excess sodium hydroxide.
Describe the precipitation reaction of Mn2+ with NaOH.
Pale pink solution reacts to form a light brown precipitate of manganese (II) hydroxide, Mn(OH)2, which darkens on standing in air.
Precipitate is insoluble in excess sodium hydroxide.
Describe the precipitation reaction of Cr3+ with NaOH.
Violet solution reacts to form a grey-green precipitate of chromium (III) hydroxide, Cr(OH)3
Precipitate is soluble in excess sodium hydroxide forming a dark green solution.
Describe the oxidation reaction of Fe2+ to Fe3+ with MnO4-.
Name the colour of the solution formed.
Fe2+ ions are oxidised by MnO4- to Fe3+. MnO4- is reduced to Mn2+.
5Fe2+ + MnO4- + 8H+ —> 5Fe3+ Mn2+ + 4H2O
Solution goes from purple to colourless.
Describe the reduction reaction of Fe3+ to Fe2+ with I-.
Name the colour of the solution formed.
Fe3+ ions are reduced by I- to Fe2+. I- is oxidised to I2.
2Fe3+ + 2I- —> 2Fe2+ + I2
Solution should go from orange-brown to pale green, but oxidation of iodide is more visible, so solution goes from orange-brown to brown instead.
Describe the oxidation reaction of Cr3+ to CrO4 2- with H2O2.
Cr3+ ions are oxidised by H2O2 to Cr6+ ions in CrO4 2-.
O is reduced from -1 in H2O2 to -2 in CrO4 2-.
2Cr3+ + 3H2O2 + 10OH- —> 2CrO4 2- + 8H2O
Solution goes from green to orange.
Describe the reduction reaction of Cr2O7 2- to Cr3+ with Zinc.
Name the colours of the solutions formed.
Cr2O7 2- ions are reduced by Zn to Cr3+. Zn is oxidised to Zn2+.
Cr2O7 2- + 3Zn + 14H+ —> 2Cr3+ + 3Zn2+ + 7H2O
Solution goes from orange to green.
In excess zinc, Cr3+ ions are further reduced to Cr2+ ions.
Zn + 2Cr3+ —> Zn2+ + 2Cr2+
Solution goes from green to pale blue.
Describe the disproportionation reaction of Cu+ ions.
Cu2O + H2SO4 —> Cu + CuSO4 + H2O
Forms Cu as a brown solid.
Forms CuSO4 as a blue solution.
Describe the reduction of Cu2+ to Cu+ with I-.
Cu2+ ions are reduced by I- to Cu+. I- is oxidised to I2.
2Cu2+ + 4I- —> 2CuI + I2
Solution goes from pale blue to brown. Forms a white copper iodide precipitate.
