3.4 D-block Flashcards
(67 cards)
1
Q
Define a d-block element
A
- group of elements whose outer electrons are found in d-orbitals
2
Q
Why do chromium and copper fill their d orbitals before s?
A
- completely full or half full d-sub shell is more stable than a partially filled d sub level
3
Q
Define a transition metal
A
- d-block element that forms a stable ion with an incomplete d-sub shell
4
Q
What is a transition metal complex?
A
- central metal ion surrounded by coordinately bonded ligands
5
Q
Define a ligand
A
- small molecule with a lone pair that can bond to a transition metal ion
6
Q
Define a complex ion
A
- a transition metal bonded to one or more ligands
7
Q
Define a coordinate bond
A
- a bind where both electrons are provided for by the same atom
8
Q
Define the coordinate number
A
- number of coordinate bonds formed
9
Q
Features of transition metal complexes
A
- small with very large positive charges
- many empty bonding orbitals
- electron-rich molecules have lone pairs so they can from coordinate bonds with empty orbitals in transition metal ion
10
Q
Monodentate and bidentate ligands
A
Mono: one atom that can bond to metal ion
Bi: 2 atoms bonding to metal ion (ligand able to donate 2 lone pairs)
11
Q
[Fe(H2O)6]2+
A
Pale green
12
Q
[Fe(H2O)6]3+
A
Yellow
13
Q
[Cr(H2O)6]3+
A
Dark green
14
Q
[Co(H2O)6]2+
A
Pink
15
Q
[Cu(H2O)6]2+
A
Blue
16
Q
[Cu(NH3)4(H2O)2]3+
A
Royal blue
17
Q
[CoCl4]2-
A
Blue
18
Q
[CuCl4]2-
A
Yellow green
19
Q
What are stereoisomers
A
- pairs of molecules with same formula but different orientation of functional groups in 3D space
20
Q
Ligand names
A
1 - mono
2 - di
3 - tri
4 - tetra
5 - penta
6 - hexa
21
Q
Ligand group names
A
H2O - aqua
NH3 - ammine
OH- - hydroxo
Cl- - chloro
F- - fluoro
CN- - cyano
22
Q
Cis isomer
A
Same side
23
Q
Trans isomer
A
Diagonal
24
Q
Where do the colours of transitional metal complexes come from?
A
- there is repulsion between electrons present in ligands and electrons in d orbitals
- which destabilises the orbitals causing them to split into 3 low energy orbitals and 2 high energy
- electrons move from low to high energy gaining energy by the absorption of light to move to higher energy level
- colours seem are due to unabsorbed frequencies
25
Properties of d-block metals
- good conductors of heat and electricity
- high melting and boiling point
- malleable
- ductile
- shiny
- strong with high tensile and compressive strength
26
Properties of transition metals
- variable oxidation states
- have catalytic activity
- form coloured complexes
- other metal properties
27
What is meant by oxidation state?
- hypothetical charge of an atom if all of its bonds to other atoms were fully ionic
28
Cr3+
Green
29
Cr2O7 2-
Orange
30
CrO4 2-
Yellow
31
Co2+
Pink
32
Fe2+
Pale green
33
Fe3+
Red brown
34
Cu2+
Pale blue
35
Explain the nature of ligands
- different ligands have different effects on the energies of the d-orbitals of the central ion
- some ligands have strong electrical fields which cause a large energy gap when d-orbitals split
36
Order of smallest to largest split
Cl-
F-
OH-
H2O
NH3
CN-
37
Impact of oxidation of metal on transition metal complexes
- as oxidation increases so does the amount of splitting of the d-orbital
- changes of oxidation state change the colour of light absorbed so therefore colour of light seen
38
Explain how the coordination of the ion impacts its splitting
- splitting is greater in octahedral than tetrahedral
- only normally change coordination if change ligand, which will change colour too
—> change cannot be isolated
39
Colour change when cobalt solution is oxidised
- rapid darkening of straw coloured to deep red brown when cobalt solution oxidised
40
Examples of transition metal catalysts
- iron in the Haber process
- nickel to make margarine in the dehydrogenation of vegetable oils
- vanadium oxide in the contact process
- manganese oxide in the catalytic decomposition of hydrogen peroxide
41
Define a homogenous catalyst and how they work
- same physical state as reactions
—> use variable oxidation states to oxidise/reduce a reactant, making it more reactive
—> the transition metal can then be converted back to its original oxidation state by reaction with another molecule
42
Define a heterogenous catalyst and how they work
- different physical state to reactants
—> partially filled d-orbitals
—> catalyst provides a solid surface on which reactants can be absorbed and brought closer together for more opportunity to react
—> molecules with lone pairs can form coordinate binds to the metal atom because there are available empty d-orbitals to bond ti
43
Reactions of Cr3+ with OH- ions
- green
- grey-green ppt when OH- added
- ppt dissolve to deep green solution when excess OH- added
44
Reaction of Fe2+ with OH- ions
- pale green
- dark green ppt when OH- added
- no further change when excess OH- added
45
Reaction of Fe3+ with OH- ions
- yellow
- red-brown ppt when OH- added
- no further change when excess OH- added
46
Reaction of Cu2+ with OH- ions
- pale blue
- pale blue ppt when OH- ions added
- no further change when excess OH- ions added
47
Reaction of Mn2+ with OH-
- pale pink solution to off white ppt
- does not dissolve in excess
48
Zn2+ reaction with OH-
- colourless solution to white ppt
- ppt dissolves in excess to give colourless solution
49
Cr3+ with NH3
- blue/purple solution to muddy green ppt
50
Mn2+ with NH3
- pale pink solution to off white ppt
- does not dissolve in excess
51
Fe2+ with NH3
- pale green solution to dark green ppt
- turns brown by aerial oxidation
52
Fe3+ with NH3
- yellow solution to reddy-brown ppt
53
Ni2+ with NH3
- pale green solution to pale green ppt
- ppt dissolve in excess to give blue solution
54
Cu2+ with NH3
- blue solution to pale blue ppt
- ppt dissolves in excess to give deep blue solution
55
Zn2+ with NH3
- colourless solution to white ppt
56
State how enthalpy of formation values give an indication of stability
- the more negative the enthalpy change the more stable the oxide
57
Describe a test to show the presence of iron (III) ions in a solution of Fe2SO4.7H2O
- add aqueous NaOH
- give red brown ppt
58
Describe how aqueous sodium hydroxide can be used to distinguish between aqueous iron (II) sulphate and iron (II) sulphate
- iron (II) ions give green ppt
- iron (III) ions give red brown ppt
59
Construct the equation for the oxidation of acidified iron (II) ions by oxygen
4Fe2+ + O2 + 4H+ —> 4Fe3+ + 2H2O
60
Explain why the H-O-H bind angle in the water ligand is 107° rather than 104.5°
- water molecules have 2 lone pairs and 2 bond pairs
- water ligands have 1 lone pair and 3 bond pairs
- lone pairs repel more than bond
61
Explain why the complex ions [Fe(H2O)6]3+ and [Fe(H2O)5(OH)]2+ are not the
same colour.
Different ligands cause different splitting therefore different frequencies of light are absorbed
62
Suggest how you would select an appropriate wavelength to find the
concentration of [Fe(H2O)6]3+ in the equilibrium mixture.
Find the wavelength absorbed by [Fe(H2O)6] but not [Fe(H2O)5(OH)]
63
Explain why CO is a good reducing agent
It has carbon in its 2+ state but its most stable state ins 4+
64
Colour change when aqueous NaOH added to potassium dichromate
Orange to yellow
65
Observations when silver nitrate is added to [CoCl4]2-
- white ppt of silver chloride
66
How would you distinguish Mg2+, Fe2+, Cr3+ and Pb2+?
- add excess NaOH
- Mg(OH)2 keeps white ppt but Pb(OH)2 dissolves
- Fe(OH)2 keeps green ppt but Cr(OH)3 dissolves
—> lead and chromium are amphoteric
67
What can be said about substances that dissolve when excess NaOH is added?
They’re amphoteric
