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IB chemistry > topic 13 - transition metals > Flashcards

topic 13 - transition metals Flashcards

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1
Q

define a transition metal

A

one which forms one or more stable ions which have incompletely filled d orbitals

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2
Q

define a transition metal

A

one which forms one or more stable ions which have incompletely filled d orbitals

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3
Q

what does this definition mean for zinc?

A

distinguishes zinc from d-block elements zinc Zn only forms the ion Zn2+, which has a configuration [Ar]3d10

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4
Q

when d sub shell is empty, 4s is at ——— than 3d

A

lower energy

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5
Q

when d sub shell is occupied, 4s is at ———- than 3d

A

higher energy

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6
Q

so in the case of ionisation, where are electrons removed from first - 4s or 3d?

A

4s

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7
Q

in the case of electron sub-shell filling, where are electrons added first - 4s or 3d?

A

4s

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8
Q

describe copper

A

[Ar]3d104s1
- can lose 4s electrons to form Cu(I)
- compounds or lose one 4s and one 3d electron to become Cu(II) compounds

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9
Q

describe scandium

A

[Ar]3d14s2
- normally forms Sc(III) ions
- therefore, it will have no electrons in the D orbital [Ar]3d04s0
- hence, scandium does not show typical properties of transition metals

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10
Q

state the 6 common properties of period 4

A
  1. generally hard metals
  2. exhibit magnetism
  3. have variable oxidation states
  4. show catalytic activity
  5. form complex ions
  6. ions are coloured
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11
Q

explain the hardness and high melting points of transition metals

A
  • result from the strong metallic bonds in the elements
  • due to their ability to release electrons from both outer and inner shells for bonding (eg metals in the first series use both 3d and 4s electrons for bonding)
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12
Q

describe the two forms of magnetism concerned with transition metals

A

paramagnetism - caused by unpaired electrons and are attracted by a magnetic field
diamagnetism - caused by paired electrons and repelled slightly by a magnetic field

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13
Q

why will all substances exhibit some diamagnetism?

A

as they have some paired electrons

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14
Q

why does paramagnetism dominate over diamagnetism?

A

the effect of the diamagnetism is much smaller than the paramagnetic effect and so in substances with an unpaired electron, paramagnetism dominates

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15
Q

the more unpaired electrons,

A

the greater the paramagnetism (magnetic moment)

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16
Q

Fe2+
[Ar]3d6

A

paramagnetism

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17
Q

Cr3+
[Ar]3d3

A

paramagnetism

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18
Q

Cu+
[Ar]3d10

A

diamagnetism

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19
Q

when a metal forms an ionic compound, what does the formula of the compound produced depend on?

A

the energetics of the process:
- the compound formed is the one in which most energy is released
- the more energy released, the more stable the compound

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20
Q

what are the two energy terms that must be considered in terms of which oxidation state will be favoured?

A
  • the amount of energy needed to ionise the metal (the sum of the various ionisation energies)
  • the amount of energy released when the compound forms (lattice enthalpy for solids, or hydration enthalpies of the ions for solutions)
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21
Q

give an example of a typical non-transition metal and its non-variable oxidation states

A

calcium chloride
- making Ca2+ ions instead of Ca+ requires greater ionisation energy, but more energy is released as lattice energy (as there is a greater attraction between chloride ions and Ca2+ ions than Ca+ ions)
- third electron comes from 3p shell which is much more difficult to remove; so although there will be a gain in lattice enthalpy, it isn’t anything to compensate for the extra ionisation energy

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22
Q

give an example of a typical transition metal and its variable oxidation states

A

iron
- the 4s orbital and 3d orbitals have very similar energy
- extra ionisation energy of increasing oxidation states is compensated by the extra lattice enthalpy/hydration enthalpy evolved

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23
Q

(VO2)+

A
  • yellow
  • 5+
  • oxovanadium (V)
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24
Q

(VO)2+

A
  • blue
  • 4+
  • oxovanadium (IV)
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25
Q

V3+

A
  • green
  • 3+
  • vanadium (III)
26
Q

V2+

A
  • violet
  • 2+
  • vanadium (II)
27
Q

what is the catalytic activity of transition elements and their compounds associated with? how does this work?

A

their variable oxidation states; transition metal ions can change their oxidation number by loss or gain of electrons. they then bind to reactants, forming intermediates as part of a chemical pathway of lower activation energy

28
Q

describe how transition metal catalysts function

A
  1. the first transition series elements have partially filled 3d-orbitals that can accept electron density from the adsorbed molecules)
  2. reactant molecules are adsorbed onto the surface of the metal and held in place while a reaction occurs
  3. after the reaction, the products are desorbed and the metal remains unchanged
29
Q

give 2 examples of reactions that are catalysed by transition metals or their compounds

A
  • metallic iron, Fe, is the catalyst in the Haber process for the synthesis of ammonia (N2 + 3H2 -> 2NH3)
  • vanadium (V) oxide, V2O5, is used in the contact process for making sulphuric acid (2SO2 + O2 -> SO3)
30
Q

how does vanadium (V) oxide function in the contact process?

A

the sulfur dioxide is oxidised by vanadium (v) oxide, which itself is reduced to vanadium (iv) oxide. the latter is then deoxidised by oxygen to vanadium (V) oxide

31
Q

define a ligand

A

an atom, molecule, radical, or ion that forms a complex by donating a pair of electrons into vacant orbitals on the central metal atom (coordinate/dative bond)

32
Q

when M^n+ ions are dissolved in water,

A

they become hydrated by aqueous ions

33
Q

define complex ions

A

the transition metal ions with ligands attached

34
Q

why is the whole complex an ion?

A

it carries a charge

35
Q

the bonds within the complex are

A

coordinate bonds

36
Q

define the coordination number

A

the number of ligands associated with the central metal ion

37
Q

give 5 common ligands

A

water (‘aqua’ when part of a complex), ammonia (ammine), hydroxide ion (hydroxo), chloride ion (chloro) and cyanide ion (cyano)

38
Q

define a unidentate ligand

A

a ligand that donates 1 pair of electrons to a complex (eg H2O, NH3, Cl-)

39
Q

define a bidentate ligand

A

a ligand that donates 2 pairs of electrons to a complex (eg ethanedioate ion, where a lone pair of electrons on each of the oxygen atoms can for coordinate bonds)

40
Q

define a multidentate ligand

A

can form several bonds with the central metal ion as it has a number of atoms with lone pairs of electrons available for bonding (eg EDTA4- which has 6 donor atoms with lone pairs, 2 on N atoms and 4 on oxygen atoms)

41
Q

what are multi dentate ligands also sometimes called?

A

chelating ligands

42
Q

why are the complexes formed by multi dentate ligands very stable?

A

because the central metal ion is held by many co-ordinates.

43
Q

state 4 typical complex ion shapes

A
  • octahedral: complexes with six smaller ligands like H2O and NH3 (eg [Co(H2O)6]2+)
  • tetrahedral: complexes with four larger ligands like Cl- (eg [CuCl4]2-)
  • square planar: complexes with two small and two large ligands (eg Ni(NH3)2Cl2]
  • linear: two ligands (eg [Ag(NH3)2]+
44
Q

how does absorption produce colour?

A

if an electro in the d sub shell absorbs wavelengths of visible light, it will reflect the colour (which we see) made up of all the other visible wavelengths minus the ones it absorbs

45
Q

if an ion or a compound has atoms with no d orbitals, or if they have a full d configuration

A

the ion/compound will absorb outside the visible region and appear colourless/white

46
Q

quantum theory

A

dE=hf

  • transition: when an electron moves to a higher energy level it absorbs an amount of energy equal to the energy difference between the two allowed energy levels
  • the energy absorbed can cover a range of frequencies; if the frequencies are in the visible region, coloured will be observed
47
Q

if the transition is larger, the radiation may fall into the

A

UV region

48
Q

if the transition is smaller, the radiation may occur in the

A

IR region

49
Q

the colour of a transition metal is associated with

A
  • incompletely filled d orbitals
  • the nature of the ligands surrounding the central cation
50
Q

how does the ligand affect the d orbitals in a free metal ion?

A
  • the degeneracy of the 3d orbitals is destroyed
  • an electron that is close to a ligand will be repelled and hence the energy of such orbitals is raised relative to the others
  • in a complex ion the 3d orbitals are split into two of higher energy and three of lower energy
  • there is an energy difference between the two sets, dE
  • on the absorption of light energy, a d electron is moved from the lower energy level to the higher energy level (d-d transition)
  • the frequency of the light that causes this transition is in the visible region, so that colour at this frequency is removed from the white light
  • the colour depends on the size of the energy gap, which varies with the metal cation and type of ligand
51
Q

explain why aqueous solutions of copper (II) ions are blue in colour

A
  • aqueous solutions of copper (II) ions contain [Cu(H2O6)2+] aqueous complex ions
  • the electronic configuration of a Cu2+ ion is [Ar]3d9
  • splitting of 3d orbitals by the ligands occurs in a complex ion
  • when white light is shone onto the solution, an electron is promoted from lower to higher level (the energy gap is dE), called a d-d transition.
  • the frequency of the light absorbed corresponds to that of red light (dE=hf)
  • the solution appears blue as white light minus red light gives blue
52
Q

why do metal ions with empty (3d0) d orbitals form colourless ions?

A

there are no d-electrons to promote

53
Q

why do metal ions with full (3d10) d orbitals form colourless ions?

A

there are no vacant orbitals to which an electron can be promoted

54
Q

the light that is reflected or transmitted to the observer’s eye is not a complete spectrum of the wavelengths that make up white light, and therefore

A

it appears to have a colour complementary to that of the absorbed light

55
Q

how does nuclear charge affect dE?

A

a larger nuclear charge will have a stronger force of attraction so more energy will be needed to move the electron from 1d orbital to another

56
Q

factors affecting dE

A
  • type and size of ligand
  • strength of metal-ligand bond in the complex
  • shape of the complex
  • coordination number
  • oxidation state
57
Q

why does the colour of a transition metal ion depend on the nature of the ligands bonded to the central metal ion?

A
  • some ligands have strong electrical fields which cause a large energy gap when the d orbitals split into 2 groups
  • the greater the splitting, the more energy needed to promote an electron from the lower group of orbitals to the higher ones
  • greater energy = shorter wavelengths of light absorbed
58
Q

as splitting increases, the light absorbed will tend to

A

shift away from the red end of the spectrum towards orange, yellow, and so on

59
Q

how does changing the oxidation state impact the colour of a ligand?

A
  • changes the number of electrons in the d levels, altering dE
  • change colour of light absorbed
60
Q

how is cobalt chloride used to detect the presence of water?

A

when water is present, cobalt forms [Co(H2O)6]2+] which is pink as it is a different ligand and coordination number to [Co(Cl4)]2- which is blue

61
Q

splitting is greater if the ion is —— than ——-

A

octahedral; tetrahedral

62
Q
A

IB chemistry (29 decks)

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