Transition metals Flashcards
What are some metallic properties of transition metals?
- All of the d-block elements are metals
- They have strong metallic bonds (high mpts + bpts)
- Small size and close packing (high density) of the ions result in strong electrostatic forces of attraction between the positive metal ions and the delocalised electrons
- They have higher melting and boiling points and higher densities than s-block
What is the electronic configuration of chromium?
[Ar] 4s1 3d5
What is the electronic configuration of copper?
[Ar] 4s1 3d10
What is the trend in first ionisation across the d-block elements?
There’s only a slight increase in 1st IEs across the d-block elements
- The nuclear charge increases
- and the shielding also increases, as the additional electron is added to 3d subshell, which shields the 4s electrons from the positive nucleus
- These two factors almost cancel each other out
Compare the successive ionisation energies of Calcium and Vanadium
For Ca, the first two IEs are relatively low as the electrons are being removed from 4s orbital. There’s a big jump between the 2nd and 3rd ionisation energies because the third electron is removed from the 3p orbital. The e- in the 3p orbital is closer to the attraction of the nucleus and experiences less shielding so more energy is needed to remove it.
For V, the 4s and 3d electrons are very close in energy so there’s no big jump in successive IEs for vanadium until the sixth electron is removed
Why are there variable oxidation states?
This is because the five inner d orbitals are at similar energy to the outer s orbital
Which compounds tend to be covalent?
Compounds and ions containing transition metals in the higher oxidation states tend to be covalent eg/MnO4- is a covalently bonded anion containing Mn in an oxidation state of +7.
Which compounds tend to be ionic?
Lower oxidation states tend to involve ionic bonding eg/MnCl2. Ionic bonding in transition metals form when 4s and then 3d electrons are lost to form positively charged ions.
Define transition metal:
A transition metal is a d-block element that forms at least one stable ion with a partially filled d-subshell
What does the stable version of Scandium look like?
Sc3+ [Ar] - no partially filled d-subshell, as the d-subshell is empty
What does the stable version of Zinc look like?
Zn2+ [Ar] 3d10 - full 3d subshell
Give the structure, shape, bond angle, coordination number and ligand of [Cu(H2O)6]2+ ?
Name: hexaaquacopper (II)
Shape: Octahedral
Bond angles: 90
Coordination number: 6
Ligand: H2O
What does the coordination number tell us?
The number of electron pairs donated to the central metal ion
Give the structure, shape, bond angle, coordination number and ligand of [Ag(NH3)2] + ?
Name: diamminesilver (I)
Shape: Linear
Bond angles: 180
Coordination number: 2
Ligand: NH3
Give the structure, shape, bond angle, coordination number and ligand of [CuCl4]2- ?
Name: tetrachlorocuprate (II)
Shape: tetrahedral
Bond angles: 109.5
Coordination number: 4
Ligand: Cl-
Give the structure, shape, bond angle, coordination number and ligand of [Ni(CN)4]2- ?
Name: tetracyanonickelate (II)
Shape: square planar
Bond angles: 90
Coordination number: 4
Ligand: CN-
What coordination number do transition metals only have?
2,4 or 6
What shape is the most common for transition metals?
Tetrahedral ones are by far the most common
When will transition metals have a square planar shape?
When it has a d8 configuration such as Ni2+, Pd2+, Pt2+
What are ligands?
A species with a lone pair of electrons that it can donate to form a dative covalent bond with a transition metal ion
What can ligands be described as?
Lewis bases because they are electron pair donors.
This means they must a lone pair of electrons. They can be neutral or negatively charged
What are bidenate ligands?
Donate two pairs of electrons to the central metal ion
Draw an example of a bidenate ligand with H2NCH2CH2NH2 (1,2-diaminoethane) group:
Draw an example of a bidenate ligand with C2O4 2- (ethanedioate ion) group:
What are multidentate/polydentate ligands?
Ligands that donate more than two pairs of electrons to the central metal ion
Give an example of a multidentate ligand?
EDTA 4- (ethylenediaminetetraacetate)
Why are transition metals/ions coloured?
- When surrounded by ligands the d-subshell splits into two
- Electrons get promoted/excited from the lower orbitals to the higher orbitals by absorbing frequencies of light within the visible region
- The colour of the complex is complementary to the absorbed light
What does the energy gap correspond to?
Frequencies within the visible spectrum
Describe how the d-to-d transition occurs?
When an ion is surrounded by ligands, some d orbitals are closer than others to the ligands, because of their distribution in space. The ligands may be roughly regarded as clouds of negative charge, which push the orbitals closest to them to slightly higher energy levels
What does the energy gap allow to happen?
For an electron to be excited from a lower energy to a higher energy d orbital as it absorbs light, provided that there is at least one electron present to be excited and that there is space for it in one of the orbitals of higher energy.
What is the condition in order for d-to-d transitions to occur, and hence for an ion to be coloured is?
The ion must have a partially filled d subshells
What transitions metals aren’t coloured?
Zn2+ and Sc3+
What does the energy difference between the split d orbitals (and hence the colour) depend on?
- The oxidation state of the metal ion
- The type of ligands
- The number of ligands
What colour of the transition metal will appear as compared to the frequency absorbed?
The colour of the transition metal complex will appear as the complementary colour to the frequency absorbed
Give the colour of the hexaaquametal ion solution of Co2+, Cu2+, Fe2+, Fe3+ and Cr3+:
Co2+ : pink solution
Cu2+ : blue solution
Fe2+ : pale green solution
Fe3+ : orange solution
Cr3+ : green solution
Give the observations when NaOH is added dropwise for Co2+, Cu2+, Fe2+, Fe3+ and Cr3+:
Co2+ : blue ppt
Cu2+ : blue ppt
Fe2+ : green ppt
Fe3+ : red-brown ppt
Cr3+ : green ppt
Give the observations when NaOH is added in excess for Co2+, Cu2+, Fe2+, Fe3+ and Cr3+:
Co2+ : ppt remains
Cu2+ : ppt remains
Fe2+ : ppt remains
Fe3+ : ppt remains
Cr3+ : ppt dissolves to give a green solution
What happens to the green ppt of Fe2+?
The green ppt starts to turn into red-brown ppt as the O2 in the air is oxidising the Fe2+ ions into Fe3+ ions. This is known as aerial oxidation
Give the observations when NH3 is added dropwise for Co2+, Cu2+, Fe2+, Fe3+ and Cr3+:
Co2+ : blue ppt
Cu2+ : blue ppt
Fe2+ : green ppt
Fe3+ : red-brown ppt
Cr3+ : green ppt
Give the observations when NH3 is added in excess for Co2+, Cu2+, Fe2+, Fe3+ and Cr3+:
Co2+ : ppt dissolves to give a brown solution
Cu2+ : ppt dissolves to give a deep blue solution
Fe2+ : ppt remains
Fe3+ : ppt remains
Cr3+ : ppt dissolves (slowly) to give a green solution
What does a deprotonation (NaOH) reaction look like? ([Cu(H2O)6]2+
[Cu(H2O)6]2+ (aq) + 2OH- (aq) –> [Cu(OH)2(H2O)4] (s) + 2H2O(l)
What is a deprotonation reaction?
When any base is added to an aqueous solution containing transition metal ions, dropwise addition always causes deprotonation
How can deprotanation be reversed?
By adding a dilute acid eg/dil. HCl
What does a protonation (NaOH) reaction look like? ([Cu(OH)2(H2O)4] (s)
([Cu(OH)2(H2O)4] (s) + 2H+(aq) –> [Cu(H2O)6]2+(aq)
What does a deprotonation (NaOH) reaction look like? ([Cr(H2O)6]3+?
([Cr(H2O)6]3+(aq) + 3OH- (aq) –> [Cr(OH)3(H2O)3] (s) + 3H2O (l)