5.3.1 Transition metals Flashcards
What are d block elements?
- between Grp 2 and 13, with highest energy electrons in 3d orbitals
- metallic: high mp and bp, shiny, and conduct electricity and heat
Write out the electronic configurations for copper and chromium?
Cr: 1s2 2s2 2p6 3s2 3p6 3d5 4s1
Cu: 1s2 2s2 2p6 3s3 3p6 3d10 4s1
for stability
Whats special about ions forming with d block elements? E.g. give electronic configuration of Fe2+
- they lose 4s e- first before losing 3d
1s2 2s2 2p6 3s2 3d6
Define transition elements
- d block elements that form at least one ion with partially filled d-orbital (scandium and zinc are NOT transition metals)
State and describe the 3 properties of transition metals
- variable oxidation numbers -> all form +2 in compounds, manganese up to +7
- coloured compounds -> colour linked to partially filled d-orbitals of transition metal ion + can vary with diff oxidation states
- catalysts
heterogenous
- haber: iron
- hydrogenation: nickel
- hydrogen peroxide decomposition: MnO2
- contact process: V2O5
homogenous
- Fe2+ ions in reaction of iodide ions and S2O8 2-.
Define ligand
molecule/ion that donates a pair of electrons to a central metal ion to form a coordinate/ dative covalent bond to form a complex
Define coordination number
indicates the no. of bonds attached to the central metal ion
What is monodentate vs bidentate? What are the key examples?
mono: donate ONE pair of electrons to central metal ion (water, ammonia, OH-, Cl-)
bi: donate TWO pairs of electrons to central metal ion (C2O4 2-, NH2CH2CH2NH2)
How do you represent complex ions?
[Cr(H2O)6] 3+
ion inside square brackets
ligand inside round brackets
What is the shape for coordination numbers:
a) 6
b) 4
c) 2
a) octahedral (90 degrees)
b) tetrahedral (109.5 degrees) or square planar (90 degrees) when there are 8 d electrons in the highest energy d sub shell
c) linear (180 degrees)
Which shape complex ions show cis-trans isomerism?
Some four (square planar) and six coordinate (octahedral) complex ions with 2 diff monodentate ligands
Which shape complex ions show cis-trans AND optical isomerism?
Some six-coordinate complex ions containing monodentate and bidentate ligands
Optical isomerism only in octahedral complexes containing 2 or more bidentate ligands e.g. 3
What is cis platin used for?
Used as an anti cancer drug since it forms a complex in a cell which binds to DNA and prevents it from replicating
Describe the cis vs trans isomer for octahedral monodentate and bidentate e.g. using angles
Cis: 90 degrees between the same type of ligand (they’re next to each other)
Trans: 180 between the same type of ligand (opposite each other)
Bidentate is the same thing
What is ligand substitution?
One ligand in a complex ion is replaced by another ligand
Copper (II) sulfate in water forms which ion?
[Cu(H2O)6] 2+
[Cu(H2O)6]2+ colour
Pale blue
Write equations for ligand substitutions of [Cu(H2O)6]2+ (e.g with ammonia and with HCl)
What happens when dropwise ammonia is added compared to excess?
EXCESS AMMONIA:
[Cu(H2O)6]2+ +4NH3 -> [Cu(NH3)4(H2O)2]2+ + 4H2O
With dropwise ammonia added, Cu(OH2) precipitate forms then dissolves in excess ammonia to form the complex ion
EXCESS CONC HCL:
[Cu(H2O)6]2+ +4CL- <-> [CuCl4]2- + 6H2O (green intermediate due to mixture of solutions)
[Cu(NH3)4(H2O)2]2+ colour
Dark blue
Cu(OH)2 Colour
Pale blue
[CuCl4]2- colour
Yellow
Water + [CuCl4]2- forms what?
Goes back to blue Colour but more dilute/paler
Why does coordination number change when HCl is added?
Since chloride ligands are larger so fewer can fit around central ion compared to water molecules in copper(II) sulfate complex ion
KCr(SO4)2 . 12H2O in water = [Cr(H2O)6]3+ and which Colour?
Violet
Cr3+ ions in solution
Green
What equations if you add excess or drop wise ammonia to [Cr(H2O)6]3+?
EXCESS: [Cr(H2O)6]3+ +6NH3 -> [Cr(NH3)6]3+ + 6H2O
DROPWISE
Cr(OH)3 forms first, then dissolves in excess ammonia
Cr(OH)3 colour
Grey-green
Why is haemoglobin important and what does CO do?
O2 and CO2 can bind and be transported around the body due to Fe2+ haem groups
CO can also bind to form carboxyhaemoglobin -> ligand substitution occurs where oxygen is replaced, and CO binds much more strongly (irreversibly) = death
What is precipitation?
Two aq solutions containing ions react together to form an insoluble ionic solid
Which ions react with NaOH to make precipitates which are insoluble in excess NaOH?
Cu2+, Fe2+, Fe3+, Mn2+
Cu2+ ions
Blue
Fe2+ ions
Pale green
Mn2+ ions
Pale pink
Fe3+ ions
Yellow
Fe(OH)2
Green
Fe(OH)3 colour
This occurs when Fe(OH)2 is exposed to air -> brown at surface
Or just orange-brown
Mn(OH)2 colour
Light brown (and darkens in air)
Which precipitate dissolves in excess NaOH and what is the equation?
Cr(OH)3 + 3OH- -> [Cr(OH)6]3-
[Cr(OH)6]3- colour
Dark green
Excess NH3 to Cu2+ and Cr3+ ions description
Form precipitates
These dissolve to form aq colored solutions
Excess NH3 to Fe2+, Fe3+, and Mn2+ ions description
Form precipitates
No dissolving
Explain why ethane-1,2-diamine can act as a bidentate ligand
(N) can donate 2 electron pairs to the central metal ion, forming 2 coordinate bonds
Explain why scandium and zinc are classified as d block elements but are NOT also transition metals (4)
Transition element: has an ION with an incomplete d sub-shell
D block since d orbital has highest energy
Sc: 1s2 2s2 2p6 3s2 3p6 3d1 4s2
Zn: 1s2 2s2 2p6 3s2 3p6 3d10 4s2
Sc3+: 1s2 2s2 2p6 3s2 3p6 -> d sub-shell empty
Zn2+: 1s2 2s2 2p6 3s2 3p6 3d10 -> d sub-shell full
