topic 15A Flashcards
(58 cards)
1
Q
be able to deduce the electronic configurations of atoms and ions of the d-block
elements of period 4 (Sc–Zn), given the atomic number and charge (if any)
A
Sc 1s22s22p63s23p64s23d1
Ti 1s22s22p63s23p64s23d2
V 1s22s22p63s23p64s23d3
Cr 1s22s22p63s23p64s13d5
Mn 1s22s22p63s23p64s23d5
Fe 1s22s22p63s23p64s23d6
Co 1s22s22p63s23p64s23d7
Ni 1s22s22p63s23p64s23d8
Cu 1s22s22p63s23p64s13d10
Zn 1s22s22p63s23p64s23d10
2
Q
what are transition metals
A
- they are d-block elements that form one or more stable ions with incompletely filled d-orbitals
3
Q
what is a d-block element
A
the outermost electrons are in a d-subshell
4
Q
why is zinc not a transition metal
A
- Zn can only form a +2 ion
- Zn2+ has a complete d orbital hence doesn’t meet the criteria of having an incomplete d orbital in one of its compounds
5
Q
why is scandium not a transition metal
A
- Sc can only form a +3 ion
- Sc3+ has an empty d orbital hence doesn’t meet the criteria of having an incomplete d orbital in one of its compounds
6
Q
trend in ionisation energy in transition metals?
A
- gradual increase from Sc to Zn until all the 4s and 3d electrons have been removed
- then there is a big jump as electrons start to be removed from the inner core electrons
7
Q
why do transition metals have variable oxidation states
A
- transition metals are able to donate and receive electrons and are able to oxidise and reduce
8
Q
why are transition metals able to oxidise and reduce?
A
- the ions contain partially filled sub-shells of d electrons that can easily lose or gain electrons
- energy differences between the oxidation states are small
9
Q
what is a ligand
A
an atom, ion or molecule which can donate a lone pair of electron
10
Q
co-ordinate bonding
A
- when the shared pair of electrons in the covalent bond come from only one of the bonding atoms
- involved in the formation of complex ions
11
Q
what is a complex ion
A
a central metal ion surrounded by ligands
12
Q
what do transition metals form in solution
A
coloured ions
13
Q
colour of Cr3+
A
blue-grey
14
Q
colour of Mn2+
A
no colour
15
Q
colour of Fe2+
A
pale green
16
Q
colour of Fe3+
A
yellow-brown
17
Q
colour of Ni2+
A
emerald green
18
Q
colour of Cu2+
A
blue
19
Q
colour of Zn2+
A
colourless
20
Q
what do colour changes arise from
A
- oxidation state
- co-ordination number
- ligand
21
Q
how does colour arise
A
- colour arises from electronic transitions from the ground state to excited state between different d-orbitals
- portion of visible light is absorbed to promote d electrons to higher energy levels
- the light that is not absorbed is transmitted to give the substance colour
22
Q
changing colour - in terms of ligands
A
- changing a ligand or changing the coordination alters the energy split between the d-orbital
- this changes the energy between the orbitals
- frequency of light being absorbed is hence changed
23
Q
why do scandium ions have no colour
A
- Sc is a member of the d block
- Sc3+ has no d electrons left to move around
- there is not an energy transfer equal to that of visible light
- hence no colour
24
Q
why do zinc ions have no colour
A
- Zn2+ ions have a full d shell
- hence there is no space for electrons to transfer
- no energy transfer that is equal to that of visible light
- so no colour is seen
25
why do Cu+ ions have no colour but Cu2+ ions do?
- Cu+ ions have a full d shell so there is no space for electrons to transfer - there is not an energy change equal to that of visible light
- Cu2+ ions have a partially filled d orbital that splits in to two energy levels
26
spectrophotometry - what is it
- visible light is absorbed to determine the concentration of coloured ions
27
spectrophotometry - method
- add an appropriate ligand to intensify colour
- make up solutions of known concentration
- measure absorption or transmission
- plot a graph of results/ calibration curve
- measure absorption of unknown and compare
28
what characteristics do transition metals have
- complex formation
- formation of coloured ions
- variable oxidation state
- catalytic activity
29
how do colour changes arise
from changes in:
- oxidation state
- co-ordination number
- ligand
- charge on metal ion
- metal
- shape
30
change in oxidation state
## Footnote
[Fe(H2O)6]3+
[Fe(H2O)6]2+
[Fe(H2O)6]3+ = pale violet
[Fe(H2O)6]2+ = green
31
change in co-ordination number
[Cu(H2O)6]2+ = blue
[CuCl4]2- = yellow
32
change in ligand
[Cu(H2O)6]2+ = blue
[Cu(H2O)2(NH3)4]2+ = deep blue
33
change in metal
[Cu(H2O)6]2+ = blue
[Fe(H2O)6]2+ = green
34
colour of [Cu(H2O)6]2+
blue
35
colour of [CuCl4]2-
green
36
colour of [Co(H2O)6]2+
pink
37
colour of [Co(NH3)6]2+
yellow
38
colour of [Co(NH3)6]3+
brown
39
what is meant by coordination number
the number of coordinate bonds formed to a central metal ion
40
monodentate ligands
these form one co-ordination bond per ligand
41
examples of monodentate ligands
H2O:
:OH-
:NH3
42
what shape are complexes with six-fold coordination
octahedral
43
why is the shape octahedral
- transition metal complexes form octahedral shapes with small ligands such as H2O and NH3
- bond angle of 90
44
what shape is formed with slightly larger ligands
tetrahedral
45
example of larger ligand
Cl-
46
what other complexes are also formed by transition metals?
square planar
47
example of square planar
cisplatin
48
what is cisplatin used as
an anticancer drug
49
how does cisplatin work
- one chlorine ligand is substituted by a water molecule
- platin binds to DNA of the cancer cells and stops them from dividing
50
generally, how does cisplatin bind to DNA
via dative covalent bonding and hydrogen bonding
51
why is cisplatin supplied as a single isomer and not mixed with the trans form
52
bidentate ligands
- two atoms with lone pairs
- they can form two coordinate bonds per ligand
53
e.g. of bidentate ligand
NH2CH2CH2NH2
54
multidentate ligands
- can form six coordinate bonds per ligand
55
e.g. multidentate ligand
EDTA4-
56
haemoglobin
- is an iron(II) complex containing a multidentate ligand
- enables oxygen to be transported in the blood
57
what reaction occurs when an oxygen molecule is haemoglobin is replaced by a carbon monoxide molecule
ligand exchange reaction
58
why is CO bad?
- toxic to humans
- the bond made between the CO and haemoglobin is stronger than that with oxygen
- this prevents the oxygen from attaching to the haemoglobin
