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chemistry > topic 15A > Flashcards

topic 15A Flashcards

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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

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2
Q

what are transition metals

A
  • they are d-block elements that form one or more stable ions with incompletely filled d-orbitals
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3
Q

what is a d-block element

A

the outermost electrons are in a d-subshell

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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
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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
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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
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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
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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
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9
Q

what is a ligand

A

an atom, ion or molecule which can donate a lone pair of electron

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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
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11
Q

what is a complex ion

A

a central metal ion surrounded by ligands

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12
Q

what do transition metals form in solution

A

coloured ions

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13
Q

colour of Cr3+

A

blue-grey

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14
Q

colour of Mn2+

A

no colour

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15
Q

colour of Fe2+

A

pale green

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16
Q

colour of Fe3+

A

yellow-brown

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17
Q

colour of Ni2+

A

emerald green

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18
Q

colour of Cu2+

A

blue

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19
Q

colour of Zn2+

A

colourless

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20
Q

what do colour changes arise from

A
  1. oxidation state
  2. co-ordination number
  3. ligand
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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
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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
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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
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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
Q

why do Cu+ ions have no colour but Cu2+ ions do?

A
  • 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
Q

spectrophotometry - what is it

A
  • visible light is absorbed to determine the concentration of coloured ions
27
Q

spectrophotometry - method

A
  • 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
Q

what characteristics do transition metals have

A
  • complex formation
  • formation of coloured ions
  • variable oxidation state
  • catalytic activity
29
Q

how do colour changes arise

A

from changes in:
- oxidation state
- co-ordination number
- ligand
- charge on metal ion
- metal
- shape

30
Q

change in oxidation state

[Fe(H2O)6]3+
[Fe(H2O)6]2+

A

[Fe(H2O)6]3+ = pale violet
[Fe(H2O)6]2+ = green

31
Q

change in co-ordination number

A

[Cu(H2O)6]2+ = blue
[CuCl4]2- = yellow

32
Q

change in ligand

A

[Cu(H2O)6]2+ = blue
[Cu(H2O)2(NH3)4]2+ = deep blue

33
Q

change in metal

A

[Cu(H2O)6]2+ = blue
[Fe(H2O)6]2+ = green

34
Q

colour of [Cu(H2O)6]2+

A

blue

35
Q

colour of [CuCl4]2-

A

green

36
Q

colour of [Co(H2O)6]2+

A

pink

37
Q

colour of [Co(NH3)6]2+

A

yellow

38
Q

colour of [Co(NH3)6]3+

A

brown

39
Q

what is meant by coordination number

A

the number of coordinate bonds formed to a central metal ion

40
Q

monodentate ligands

A

these form one co-ordination bond per ligand

41
Q

examples of monodentate ligands

A

H2O:
:OH-
:NH3

42
Q

what shape are complexes with six-fold coordination

A

octahedral

43
Q

why is the shape octahedral

A
  • transition metal complexes form octahedral shapes with small ligands such as H2O and NH3
  • bond angle of 90
44
Q

what shape is formed with slightly larger ligands

A

tetrahedral

45
Q

example of larger ligand

A

Cl-

46
Q

what other complexes are also formed by transition metals?

A

square planar

47
Q

example of square planar

A

cisplatin

48
Q

what is cisplatin used as

A

an anticancer drug

49
Q

how does cisplatin work

A
  • one chlorine ligand is substituted by a water molecule
  • platin binds to DNA of the cancer cells and stops them from dividing
50
Q

generally, how does cisplatin bind to DNA

A

via dative covalent bonding and hydrogen bonding

51
Q

why is cisplatin supplied as a single isomer and not mixed with the trans form

A
52
Q

bidentate ligands

A
  • two atoms with lone pairs
  • they can form two coordinate bonds per ligand
53
Q

e.g. of bidentate ligand

A

NH2CH2CH2NH2

54
Q

multidentate ligands

A
  • can form six coordinate bonds per ligand
55
Q

e.g. multidentate ligand

A

EDTA4-

56
Q

haemoglobin

A
  • is an iron(II) complex containing a multidentate ligand
  • enables oxygen to be transported in the blood
57
Q

what reaction occurs when an oxygen molecule is haemoglobin is replaced by a carbon monoxide molecule

A

ligand exchange reaction

58
Q

why is CO bad?

A
  • 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

chemistry (28 decks)

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