3.2.5- Transition metals (PAPER 1) Flashcards
What is a transition element?
A d-block element that can form at least 1 stable ion with a partially filled d-subshell, less than 10 electrons.
Why is zinc not a transition element?
Zinc ions only have one oxidation state, when zinc loses its 2 outer electrons, it forms a Zn2+ ion with a full d sub-shell. Only forms one stable ion of Zn2+
Why is scandium not a transition element?
It only forms one stable ion of Sc3+, which has an empty d sub-shell, it is not partially filled.
Write the electron configuration for Fe and for Fe3+
Fe= 1s2 2s2 2p6 3s2 3p6 4s2 3d6
Fe3+ = 1s2 2s2 2p6 3s2 3p6 3d5
3 electrons removed, 2 from 4s sub-shell as lower in energy
Why do transition metals have variable oxidation states?
The electrons are in 4s and 3d energy levels which are very close in energy, means electrons are gained and lost using a similar amount of energy.
What are the colours of different vanadium ions? YBGV
VO2 + =yellow (you)
VO 2+ =blue (big)
V 3+ =green (giant)
V 2+ =violet (viking)
What are the colours of Cr 3+ and Cr2O7 2- ?
Cr 3+ = green/ violet when surrounded by 6H2O
Cr2O7 2- = orange
What are the colours of Mn 2+ and MnO4 - ?
Mn 2+ = pale pink
MnO4 - = purple
What are the colours of Fe 2+ and Fe 3+?
Fe 2+ = pale green
Fe 3+ = yellow
What is the colour of Co 2+?
Pink
What is the colour of Ni 2+?
Green
What is the colour of Cu 2+ ?
Blue
What is the colour of Zn 2+?
Colourless as full d-orbital
What is a ligand?
An ion, atom or molecule that has at least 1 lone pair of electrons: can be monodentate, bidentate or polydentate.
What are monodentate/ unidentate ligands?
Ligands with only one lone pair of electrons.
What are the 3 examples of unidentate ligands?
H2O:
:NH3
:Cl- (LARGEST)
What are bidentate ligands?
Ligands with 2 lone pairs of electrons.
Draw and name 2 examples of bidentate ligands?
Ethanedioate- C=C, each c single bonded to O with lone pair and double bonded to other O
Ethane-1,2-diamine- CH2-CH2, each c bonded to NH2
What are multidentate ligands?
Ligands which have more than 1 coordinate bonds?
What are the 2 examples of multidentate ligands?
Haem- from haemoglobin
EDTA4- - can form 6 coordinate bonds with central metal ion.
What is a complex ion?
Where a central transition metal ion is surrounded by ligands bonded by dative covalent bonds.
Ligands have at least 1 lone pair of electrons to form coordinate bond, arrow from each ligand to central metal ion, square bracket with overall charge of complex.
What is the complex shape dependant on?
The size of the ligands and the coordination number.
What is the coordination number?
The number of coordinate bonds in a complex, not the number of ligands.
eg 3 ligands may still have 6 coordinate bonds as they may be bidentate, some ligands may be smaller than others.
What shape do complexes with coordination number 6 form? Eg Co[(H2O)6]2+ (aq)
Octahedral shapes.
Draw and name complex shape of cobalt surrounded by 6 ammonia ligands
Co[(NH3)6]2+
What shape do complexes with coordination number 4 form?
Tetrahedral or square planar.
What is the name/ diagram of specific square planar complex?
cis-platin anti cancer drug
Pt[(NH3)2(Cl)2] (aq)
Central Pt, 2 dotted lines from 2 Cl:
2 wedged lines from 2 :NH3
bond angles 90
Draw the tetrahedral complex for [CuCl4]2- (aq)
Central Cu atom, 1 Cl: on top, 3 :Cl n bottom, straight, dotted, wedged line
bond angles 109.5
What shape do complexes with coordination number 2 form?
Linear shapes
Draw the linear complex of [Ag(NH3)2]+ (aq) tollen’s reagent
Ag in middle, 2 arrows from 2 :NH3 either side, square brackets
bond angles 180
How to work out oxidation state of transition metal in middle of complex?
Total oxidation state of metal= total oxidation state- oxidation state of ligands
Work out the oxidation state of Cu in [Cu(Cl)4] 2-
Overall charge 2-
4 ligands, each Cl has -1, -4 altogether
-2 - (-4)= +2 oxidation state Cu
What is the octahedral structure of haemoglobin?
Fe in middle
:OH2/:O2 at top
4 :N in middle coming from one multidentate ligand haem
1 :N on bottom from large globin protein
How does haemoglobin transport oxygen?
O2 substitutes the water ligand in the lungs where O2 conc is high to form oxyhaemoglobin which is transported around the body.
Oxyhaemoglobin gives up O2 when needed, water takes up place and haemoglobin returns back to lungs.
At the top of haemoglobin, either :OH2 or :O2 is joined.
How does carbon monoxide bind to haemoglobin?
Water ligand at top of haemoglobin replaced with :CO ligand
CO bonds strongly so not easily replaced by oxygen or water, oxygen cannot be transported so poisonous.
Which complex ions can show optical isomerism?
Octahedral complexes with 3 bidentate ligands- exist as 2 non superimposable mirror images.
Which complex ions can show cis-trans isomerism?
Octahedral complexes with 4 of the same ligands, and 2 other ligands which are the same.
Or square planar complexes
Draw the 2 cis-trans isomers: Trans- [Co(H2O)4Cl2] (aq) and Cis- [Co(H2O)4Cl2] (aq)
Trans isomer
2 different ligands (2 :Cl) are opposite eachother
Cis isomer
2 different ligands (2 :Cl) are directly adjacent eachother
How can square planar complexes display cis-trans isomerism?
If they have 2 ligands of same type, and 2 ligands of different type
Draw the cis-trans isomers of [Pt(NH3)2Cl2]
Transplatin/ trans isomer- 2 different isomers are opposite the Pt
Cisplatin/ cis isomer- 2 different isomers are next to eachother
How does the d orbital split when ligands bond with central metal ion?
Before ligand bonding, all electrons are in orbitals in same energy level (d shell)
If ligands bond, d orbital splits in 2 creating an energy gap ΔE, when e- absorb light energy some move from lowest energy level to higher energy level orbitals (ground to excited)
This requires a partially full d shell
What is required for d subshell to split?
Energy from light must equal ΔE
What does size of ΔE depend on?
-the central metal ion and its oxidation state
-the type of ligand
-coordination number (n of coordinate bonds/ shape of ion)
What is the formula for energy absorbed by the electrons?
ΔE = hv = hu/λ
Change in energy (J) = Planck’s constant (6.63x10-34Js) x frequency of light absorbed (Hz) = Speed of light (3x10^8 ms-1) / wavelength of light absorbed (m)
How do coloured complexes form?
Some frequencies of visible light are absorbed by transition metal complexes, the frequencies absorbed depend on size of ΔE
Larger the energy gap (ΔE), higher the frequency of light absorbed.
What occurs with the frequencies that are not absorbed?
They are reflected or transmitted.
The combination of the frequencies not absorbed create a complementary colour.
Eg- why does [Cu(H2O)6]2+ produce light blue?
This compound absorbs frequencies that produce red light, the remaining frequencies not absorbed produce the light blue colour.
Write the complementary colour wheel
Why are complexes with full/ empty 3d sub shells colourless/ white?
No electrons can migrate to the higher energy level
How does ligand substitution of [Co(H2O)6]2+ to [Co(NH3)6]2+ change the colour?
The coordination number and shape (octahedral) is the same
Equation- [Co(H2O)6]2+ (aq) + 6NH3 (aq) —-> [Co(NH3)6]2+ (aq) + 6H2O (l)
Colour change from pink to yellow
How does ligand substitution, coordination number and shape change affect the colour of [Cu (H2O)6] 2+ to [CuCl4]2- ?
Usually occurs when smaller ligand substituted by larger ligand
[Cu (H2O)6] 2+ (aq) + 4Cl- (aq) —> [CuCl4]2- (aq) +6H2O (l)
pale blue and octahedral to yellow and tetrahedral
How does oxidation state change affect the colour of [Fe(H2O)6]2+ (aq) to [Fe(H2O)6]3+ ?
[Fe(H2O)6]2+ (aq) —> [Fe(H2O)6]3+ (aq)
Ligands and coordination numbers remain the same
pale green and octahedral to yellow and octahedral
Same with vanadium
Describe the method for colorimetry measuring the conc of transition metal ions in solution?
1) Calorimeter set to 0 by measuring absorbance of blank sample (solvent using to dissolve transition metal ion)
2) White light filtered into narrow frequency range, monochromatic light produced. Colour produced must be absorbed by metal ion solution.
3) Monochromatic light passes through sample, some light absorbed, sample held in vessel/ cuvette.
4) Light not absorbed travels to detector which measures level of absorbance by comparing to absorbance in blank sample.
How is calibration graph used to measure conc of transition metal solution?
Calibration curve created by making range of known diff conc of transition metal solution- absorption measured for each one.
Samples made by diluting diff conc of metal ion- same metal ion and solvent as one being tested.
Test sample we want to know conc of by measuring absorbance, use graph and absorbance to find conc of metal ion in solution.
What 2 functions can ammonia have?
Bronsted lowry base- proton acceptor (small amounts dilute ammonia solution)
Ligand- can replace H2O molecules as similar in size (excess/ concentrated ammonia)
What occurs when ammonia reacts with a hexaaqua ion?
Initially- acts as Bronsted lowry base and removes H+ ions, if 3+ ion, 3H+ removed, 3NH4+ produced
If 2+ hexaaqua ion, 2H+ removed, 2NH3 react and 2NH4+ produced
precipitate of metal (II) or (III) hydroxide formed!!!!!!!!!!!!!
Some (II) ions- eg copper (II), cobalt (II), iron (II) undergo ligand substitution where NH3 replaces H2O
What are the equations for reactions of [Fe(H2O)6] 3+ and [Al(H2O)6] 3+ with excess NH3?
[Fe(H2O)6] 3+ + 3NH3 —–> [Fe(H2O)3(OH)3] + 3NH4+
ORANGE SOLUTION- BROWN PRECIPITATE
[Al(H2O)6] 3+ + 3NH3 ——> [Al(H2O)3(OH)3] + 3NH4+
COLOURLESS SOLUTION- WHITE PRECIPITATE
What is the equation for reaction between [Fe(H2O)6] 2+ and NH3?
[Fe(H2O)6] 2+ + 2NH3 ——> [Fe(H2O)4(OH)2] + 2NH4+
GREEN SOLUTION- GREEN PRECIPITATE
Write the 2 equations for the reaction of [Cu(H2O)6] 2+ and NH3: dropwise and excess
Overall: [Cu(H2O)6] 2+ + 4NH3 —–> [Cu(H2O)2(NH3)4] 2+ + 4H2O
Write the 3 equations for the reaction of [Co(H2O)6] 2+ and NH3: dropwise, excess and overall
Dropwise: [Co(H2O)6] 2+ + 2NH3 ——-> [Co(H2O)4(OH)2] + 2NH4+
PINK TO BLUE- HYDROLYSIS
Excess: [Co(H2O)4(OH)2] + 6NH3 ————–> [Co(NH3)6] 2+ + 4H2O + 2OH-
BLUE TO YELLOW- SUBSTITUTION
Overall: [Co(H2O)6] 2+ + 6NH3 ———> [Co(NH3)6] 2+ + 6H2O
PINK TO YELLOW- OVERALL SUBSTITUTION
