5.3.2 Transition Metals and Their Chemistry Flashcards
Where are transition elements found?
In the d-block.
Name all the transition elements you need to know about.
Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel and Copper.
Where are the highest energy electrons in the first row transition elements?
In the 4s and 3d subshells.
How many 4s and 3d electrons does iron have?
26-18 = 8
Which electron subshells are filled first in transition elements?
4s except in chromium and copper.
Which elements do not have a full 4s subshell?
Copper and Chromium.
Give the subshell notation of the electronic configuration of vanadium.
[Ar] 3d3 4s2
What is the definition of a transition metal?
One that can form one or more stable ions with a partially filled d-subshell.
Why are scandium and zinc transition metals?
Because they do not form stallions with a partially filled d-subshell.
Give the subshell notation for Sc3+ and explain why it is not a transition ion.
[Ar] the d-subshell is empty.
Why isn’t Zn2+ a transition ion?
Because zinc loses both the 4s electrons first, leaving a full d-subshell.
When a transition metal forms a positive ion, which electrons are removed first?
The 4s electrons.
What are the successive ionisation energies of transition metals evidence for?
Their electronic configuration.
The first ionisation energy from Sc to Cu is roughly the same, what doe this show?
Transition elements all have similar electronic structure, and lose electrons form the same shell, 4s.
Describe the trend of second ionisation energy across the transition elements.
It steadily increases across the elements which Cr and Cu being slightly higher than expected.
Why are the second ionisation energies of Cr and Cu slightly higher than expected?
Because the electron is taken from much nearer to the nucleus, the 3d shell, so more energy is needed to remove it.
Describe the third ionisation energy of the transition elements.
It steadily increase across the elements but steps down slightly at iron.
What causes the step down at iron of third ionisation energies across the transient elements.
From iron onward the electron is removed from a paired 3d orbital, which is slightly easier due to electron repulsion.
Give four special chemical properties of transition elements.
They can form complex ions. They form coloured ions in solution. They can act as good catalysts. They can exist in variable oxidation states.
What is a complex ion?
A metal ions surrounded by dative covalently bonded ligands.
What is a dative covalent bond?
A covalent bond where both electrons in the shared pair come from the same atom.
What is a ligand?
An atom, ion or molecule that donates a pair of electrons to the central metal ion.
What is the coordination number of a complex ion?
The number of dative covalent bonds that are formed with the central metal ion.
Give two common coordination numbers that your need to learn about.
4 and 6
Name three small ligands that usually result in a coordination number of 6.
H2O, CN- and NH3.
What is a metal-aqua complex ion and how is it formed?
Six water molecules forming dative covalent bonds with a metal ion. They occur when transition metal compounds dissolve in water.
Give one example of a larger ligand, which usually results in a coordination number of 4.
Cl-
What is the name for when one ligand is swapped for another, and what is the result of this?
Ligand substitution. It usually causes a colour change.
What shape are complex ions with 6 dative covalent bonds?
Octahedral.
What shape are the majority of complexes with 4 dative covalent bonds?
Tetrahedral.
Name a shape that complexes with 4 dative covalent bonds can take other than tetrahedral.
Square planar.
Give two examples of tetrahedral complexes.
[CuCl4]2- and [CrCl4]-
Give two examples of square planar complexes.
Cis/transplatin, [Pt(NH3)2Cl2]. Cisplatin is used in chemotherapy.
How many dative covalent bonds so linear complexes have?
2
Give two examples of linear complexes.
[CuCl2]- and [Ag(NH3)2]+
What does the overall charge of a complex represent?
Its total oxidisation state.
How can you calculate the oxidation state of the metal ion?
Total oxidation state - sum of oxidation states of the ligands.
What is the oxidation state of the CN- ion?
-1
What is required for a ligand to form a dative covalent bond?
A lone pair of electrons.
What is the name for ligands with one lone pair that forms a dative covalent bond with the metal ion?
Monodentate ligands (unidentate).
What is the name for ligands with two lone pairs?
Bidentate ligands.
What is the name for liagdns with more than tow lone pairs?
Polydentate ligands.
Give an example of a hexadentate ligand.
EDTA4-
Name a polydentate ligand found in the human body.
Haemoglobin.
What happens to the 3d subshell when a complex is formed?
The repulsion between 3d electrons and the ligands increase the energy of all 3d orbitals but some more than others, splitting them into two different energy levels.
Why are complexes coloured?
Electrons can jump move up to the higher energy level in the 3d orbital by absorbing visible light (photons). The colour of light absorbed is the complement of the colour that the ion appears to be.
The complex [Cu(H2O)6]2+ absorbs yellow light. What colour would a solution of this complex be?
Blue.
How many 3d electrons must a central metal ion have for it to form a coloured complex solution?
Between 1 and 9.
Name the factors that affect the colour of a complex.
The central metal ion, the ligand and the coordination number, since they affect the size of the energy gap.
What is the name for when ligands of a complex are swapped for different ligands?
Ligand exchange.
What happens when you add ammonia solution to
[Cu(H2O)6]2+(aq)? This solution is blue to start with.
Partial ligand substitution forms [Cu(NH3)4(H2O)2]2+(aq) and water. This complex is elongated octahedral and makes a deep blue solution.
What happens when you aadd SO4`2- ions to
[Cr(H2O)6)]3+(aq). This solution is initially violet.
It becomes [Cr(H2O)5(SO4)]+(aq) and water. The complex is a distorted octahedral shape and forms a green solution.
When can’t ligand exchange reactions be reversed?
When the new complex ion is much more stable than the previous one.
Give an example of a monodentate ligand that forms strong dative covalent bonds with Fe3+ ions.
CN-
Which types ligands form particularly strong dative covalent bonds with transition metals?
Bidentate and polydentate ligands.
Explain why reactions where bidentate ligands replace monodentate ligands are thermodynamically favourable.
There are generally more product molecules than reactant molecules, increasing total entropy of the system.
What happens when you add an alkali to metal aqua-ions?
A precipitate forms.
Give the three equilibriums which show how adding OH- solutions of metal aqua-ions produces insoluble metal hydroxides.
[M(H2O)6]3+ + H2O ⇋ [M(H2O)5(OH)]2+ + H3O+
[M(H2O)5(OH)]2+ + H2O ⇋ [M(H2O)4(OH)2]+ + H3O+
[M(H2O)4(OH)2]+ + H2O ⇋ [M(H2O)3(OH)3]+ + H3O+
OH- ions remove H3O+.
Why does adding small amounts of ammonia have the same effect as adding small amounts of strong alkali?
When ammonia dissolves in water OH- ions are produced:
NH3 + H2O ⇋ NH4+ + OH-
Which metal aqua-ion solutions are green?
Fe2+ and Ni2+
What colour is a solution of Cu2+ aqua-ions?
Blue
What colour is a solution of Fe3+ aqua-ions?
Yellow
What colour is a solution of Cr3+ aqua-ions?
Violet but can be green due to impurities.
What colour is a solution of Mn2+ aqua-ions?
Very pale pink.
What colour is a solution of Zn2+ aqua-ions?
Colourless.
Which ions form precipitates with OH-/NH3 with colours that differ from their aqua-ion solutions? Give the corresponding precipitate colour.
Cr3+, green and Mn2+, brown.
Which transition ions form solutions when excess OH- is added? Give the colours of the solutions.
[Cr(OH)6]3- green and [Zn(OH)4]2- colourless.
Which transition ions form solutions when excess NH3 is added? Give the colours of the solutions.
[Cu(NH3)4(H2O)2]2+ deep blue, [Cr(NH3)6]3+ purple, [Ni(NH3)6]2+ blue and [Zn(NH3)4]2+ colourless.
What are the common oxidation states of copper ions?
+1 or +2
Which copper ions are stable in aqueous solution?
Cu2+ ions
Which type of metals reduce copper ions to Cu metal? What is the name for this type of reaction?
More electropositive metals such as zinc.
What happens to Cu+ ions in aqueous solution?
They disproportionate to Cu2+ ions and Cu because they are unstable.
Why can copper(I) ions form stable complexes such as [CuCl2]-?
The ligands stabilise the copper(I) and prevent it from disproportionating.
Why aren’t copper(I) complex coloured?
Because they have a full 3d subshell.
What colour is the solid copper(I) oxide?
Red.
Give the equation for Cu+ ions disproportionating.
2Cu+(aq) → Cu2+(aq) + Cu(s)
What is the Eº cell value for the disproportionation for Cu+ ions? What does this mean?
+0.37V, it is likely to happen.
What are the common oxidation states of chromium ions?
+2, +3 and +6
Why is chromium used in steel?
To make it stainless and harder.
List the oxidation states of chromium from most stable to least stable.
+3 is the most stable, then +6 and +2 is the least stable.
Give the two ions chromium forms with copper and give its oxidation number and colour of these ions.
Cr2O72- orange (+6) and CrO42- yellow (+6).
What colour are Cr2+ ions in water?
Blue
What colour are Cr3+ ions in water?
Violet but they often appear green because the water ligands are substituted by impurities.
Which reagents can you use to reduce dichromate(VI) ions to chromium(III) ions?
Zinc and dilute acid.
Which reagents can you use to reduce chromium(III) ions to chromium(II) ions? Give the conditions required.
Zn(s) in an inert atmosphere.
Which reagents can you use to oxidise chromium(II) ions to chromium(III) ions? Give the conditions required.
Air.
Which reagents can you use to oxidise chromium(III) ions to chromate(VI) ions?
Hydrogen peroxide in an alkaline solution.
Give the equation to show oxidation of chromium(III) ions to chromate (VI) ions.
2Cr3+(aq) + 10OH-(aq) +H2O2(aq) → 2CrO4`2-(aq) + 8H2O(l)
Which reagents can you use to convert dichromate(VI) ions to chromate(VI) ions?
Strong alkali.
Which reagents can you use to convert chromate(VI) ions to dichromate(VI) ions?
Strong acid.
Why is chromium(II) ethanoate tricky to produce?
Because chromium(II) oxidises very easily.
Give the equation for the formation of chromium(II) ethanoate.
2Cr2+ + 4CH3COO- +2H2O → [Cr2(CH3COO)4(H2O)2]
What is the first step of the synthesis of chromium(II) ethanoate?
Slowly add hydrochloric acid to a flask with chromium(III) chloride solution and a zinc mech. The reduction will produce hydrogen gas which can escape through a rubber tube into a beaker of water.
What is the second step of the synthesis of chromium(II) ethanoate?
Stop hydrogen gas escaping when the solution turns blue, the buildup of pressure should force the Cr2+ solution into a flask of sodium ethanoate.
What is the third step of the synthesis of chromium(II) ethanoate?
A red precipitate will form. Wash it with water, ethanol then ether in an inert atmosphere of nitrogen.
What is an amphoteric substance?
One that can react with both acids and alkalis.
Give an example of an amphoteric complex.
Chromium hydroxide [Cr(H2O)3(OH)3]
What is formed when excess alkali is added to chromium hydroxide?
[Cr(OH)6]3-(aq) + 3H2O(l) This is not ligand exchange, the ligands are chemically modified by the OH- ions.
What is formed when acid is added to chromium hydroxide?
[Cr(H2O)6]3+ This is not ligand exchange, the ligands are chemically modified by the OH- ions.
Why do transition metals make very good catalysts?
They can use their s and d orbitals to form bonds with reactants and because their oxidation state changes easily.
What do catalytic converters do?
Convert nitric oxide and carbon monoxide to nitrogen and carbon dioxide.
Give the equation for the reaction that occurs in a catalytic converter.
2NO(g) + 2CO(g) → N2(g) + 2CO2(g)
Which two transition metals are used in catalytic converters?
Platinum and rhodium.
How do solid catalysts work?
Reactant molecules bond with the solid catalyst, adsoption. The bonds between the reactant’s atoms are weakened and they break up, forming radicals which bond together and form new molecules.
Why are catalysts usually used in the form of a mesh or fine powder?
To increase surface area.
Give two equations to show the role of vanadium in the contact process and give the overall equation.
V2O5(s) + SO2(g) → V2O4(s) + SO3(g)
2V2O4(s) + O2(g) → 2V2O5(s)
2SO2(g) + O2(g) → 2SO3(g)
Give the benefits of catalysing an industrial chemical process.
They make the process more environmentally friendly by allowing the reactions to take place at lower temperatures and pressures and can sometimes have a higher atom economy, reducing waste.
How was ethanoic acid originally made? What were the downsides of their process?
Oxidation of butane. It had a low atom economy, processing lots of waste products.
Which catalysts are used now to make ethanoic acid from carbon monoxide and methanol?
Iridium and iodine.
Give five applications of transition metals.
Construction, jewellery, paint pigments, chemotherapy and polychromic sunglasses.
Explain how cisplatin is used against a variety of cancers.
It prevents cells from dividing by cross linking the DNA, preventing it from being able to replicate so the cell dies.
Give two downsides of using cisplatin to treat cancer.
It can suppress the immune system and cause damage to the kidneys.
How do polychromatic sunglasses work?
They are embedded with a silver halide that breaks down to form silver atoms in the presence of UV light. The process reverses in absence of UV light.
Describe the appearance of copper (II) oxide, CuO.
A black solid.
Describe the appearance of copper metal.
A pink solid.
How many NH3 ligands will there be in the complex ion formed when excess NH3 is added to a metal aqua-ion solution of copper (II).
4
How many NH3 ligands will there be in the complex ion formed when excess NH3 is added to copper(I) iodide solution.
2
Why does shaking a solution of [Cu(H2O)4(NH3)2]+ make [Cu(H2O)2(NH3)4]2+
Copper(I) is unstable and can be oxidised by air.
