Chemistry of D-block Flashcards
What is the d-block?
The groups of elements whose outer electrons are found in d-orbitals.
What is a transition element?
A metal that possesses a partially filled d sub-shell in its atom or stable ions.
Which element in the d-block is not considered a transition element?
Zinc, as it has a filled d sub-shell and maintains this in its compounds.
What is the order of filling electron orbitals for d-block elements?
Fill 4s, then 3d then 4p.
Which elements in the d-block do not obey the electron filling rules?
Chromium and Copper as they each have one electron in the 4s orbital, leading to a more stable configuration since shells are more stable if they are filled or half-filled.
How are electrons lost when forming d-block ions?
4s electrons are lost first because 4s and 3d energy levels are close together so it is more energetically favourable to lose the 4s electrons before the 3d electrons.
What do the oxidation states of the d-block elements look like?
They have a large range of oxidation states because the energies of the 4s and 3d orbital are very close together, so it takes a similar amount of energy to remove any of these electrons.
What happens when the transition metals form compounds?
Energy is released, either through the formation of covalent bonds or when an ionic lattice is formed,
What does the oxidation state of each transition metal depend on?
Many factors, such as the oxidising power of the other atoms in the compounds.
How do transition metals form bonds with ligands?
The metal has an empty orbital and the ligand has a lone pair
The two atomic orbitals overlap to form a molecular orbital
A coordinate bond is formed
What is a ligand?
A small molecule with a lone pair which can form a bond to a transition metal.
Give examples of ligands
H2O, NH3, Cl- and CN-
What is a complex?
A combination of the transition metal ion and the ligands.
What are the two shapes transition metal complexes can possess?
Six ligands arranged octahedrally around the metal atom (most common)
Four ligands arranged tetrahedrally around the metal atom (less common)
Give examples of octahedral complexes
[Fe(H2O)6]2+ - pale green complex
[Fe(H2O)6]3+ - yellow complex
[Cu(H2O)6]2+ - blue complex
[Cr(H2O)6]3+ - dark green complex
[Co(H2O)6]2+ - pink complex
Give examples of tetrahedral complexes
[CuCl4]2- - yellow/green complex
[CoCl4]2- - blue complex
What factors influence the shape of the complex?
The metal
The oxidation state of the metal and the ligands
Describe the shape of [Cu(H2O)6]2+ and [Co(H2O)6]2+
Present in most aqueous solutions of Cr2+ and Co2+. Octahedral shape with one lone pair on each oxygen atom of the H2O bonded to the metal.
Describe the shape of [Cu(Nh3)4(H2O)2]2+
Addition of ammonia to a solution containing [Cu(H2O)6]2+ causes four ammonia molecules to replace water molecules creating a royal blue octahedral complex which has two arrangements. In the trans isomer, the two water molecules are opposite each other (most common). In the cis isomer, the two water molecules are next to each other.
Describe the shape of [CuCl4]2- and [CoCl4]2-
Tetrahedral complexes formed when copper(II) or cobalt (II) ions react with concentrated HCL which displaces the water molecules.
What colour change occurs when forming [CuCl4]2- and [CoCl4]2-?
Copper (II) goes from pale blue to yellow/green
Cobalt (II) goes from pink to blue
What happens when a transition metal ion is exposed to a mixture of ligands?
The ligands can be exchanged to form new complexes in an equilibrium process.
How can we view LeChateliers principle with transition metals?
There could be a colour change or a change in coordinate geometry.
Are transition metals coloured?
No, only their complexes are coloured due to the ligands having a dramatic effect of the orbitals in the metal atom.
What are the five degenerate d-orbitals for metal atoms?
dxz
dxy
dyz
dx2-y2
dz2
How does the presence of ligands affect the orbital shape of the transition metal?
The ligands approach the transition ion along the directions of the three axes. Their negative charges repel the electrons in the orbitals that point along these axes, which makes the orbitals less stable. The orbitals that do not point along the axes are not made less stable. So the overall energies of the orbitals is not the same.
What happens when the transition metal orbital energies are no longer the same?
The d-orbital splits giving two sets of orbitals close together in energy.
After the splitting of the d-orbitals, what gives transition metal complexes their colours?
Electrons being promoted from the lower state orbital to the higher state orbital by absorbing light energy that corresponds to the energy gap between orbitals.
Why are there many different colours observed in complexes?
Due to the amount of splitting between d-orbitals varying between complexes. As the splitting varies, so does the frequency of light absorbed which leads to different colours.
What is the effect of splitting on electronic structure?
In the split orbitals, the lower three orbitals are filled first with one electrons each, before the electrons pair up. Once these three orbitals are filled, the higher two orbitals are filled.
Why are some complexes colourless?
Copper (I) complexes have a full d sub-shell which means there are no empty orbitals to allow electrons to move between energy levels, so the complex appears colourless.
Scandium (III) ions have an empty d sub-shell so there are no electron to move between d-orbitals.
What is a catalyst?
Substances which increase the rate of a chemical reaction by providing an alternative pathway with a lower activation energy.
What is a homogenous catalyst?
Catalysts that are in the same physical state as the reactions that they catalyse.
What is a heterogenous catalyst?
Catalysts that are in a different physical state from the reactions that they catalyse.
Give examples of transition metals used as catalysts
Iron - the Haber process, to produce ammonia from nitrogen and hydrogen
Nickel - the hydrogenation of vegetable oils to form margarine
Platinum - the oxidation of ammonia to form nitric acid
Give examples of transition metal complexes used as catalysts
Vanadium oxide (V2O5) - the contact process for the production of sulphuric acid
Manganese dioxide (MnO2) - the catalytic decomposition of hydrogen peroxide
Why is having partially filled d-orbitals useful for a catalyst?
The empty orbitals can combine with other molecules. Molecules with lone pairs can form coordinate bonds to the metal atom to form complexes and this can increase the reactivity of the species bonded to the metal, or bring two reacting molecules closer together. This makes a reaction more likely.
Why is having variable oxidation states useful for a catalyst?
This allows the metal ion to act as a catalyst in redox reactions. It can act as an oxidising or reducing agent, then return to its original oxidation state by reaction with another molecules. It therefore appears unchanged at the end of the reaction.
How can transition metals act as heterogenous catalysts?
They are typically solids that provide a surface for molecules to be adsorbed and come together in an advantageous arrangement.
How can transition metals act as homogenous catalysts?
They typically use their variable oxidation states to oxidise/reduce a reactant which makes it much more reactive.
What are the factors making transition metals good catalysts?
Their partially filled d-orbitals and their variable oxidation states.
What happens when transition metal ions are in aqueous solutions?
They are present as hydrated metal complexes, [M(H2O)6]n+
Why are hydrated complexes acidic?
Due to the high positive charge density on the complex ion.
What does adding alkali do to the hydrated complex?
Removes the H+ as H2O and the reaction can progress further to the metal hydroxide, which is insoluble.
Why is chromium (III) hydroxide amphoteric?
It can react with both an acid and a base. It can donate H+ to the hydroxide ions and accept H+ from the water.
What happens when you add some OH- to [Cr(H2O)6]3+?
A grey-green precipitate of [Cr(H2O)3(OH)3] is formed.
What happens when you add some OH- to [Fe(H2O)6]2+?
A dark green precipitate of [Fe(H2O)4(OH)2] is formed.
What happens when you add some OH- to [Fe(H2O)6]3+?
A red-brown precipitate of [Fe(H2O)3(OH)3] is formed.
What happens when you add some OH- to [Cu(H2O)6]2+?
A pale blue precipitate of [Cu(H2O)4(OH)2] is formed.
What happens when you add excess OH- to [Cr(H2O)6]3+?
The precipitate dissolves to give a deep green solution of [Cr(OH)6]3-.
