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principle of transition metals Flashcards

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1
Q

what is a transition metal

A

elements with an incomplete d-subshell that can form at least one stable ion with an incomplete d-subshell

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1
Q

what are general properties of transition elements

A

Variable oxidation states
Form complex ions
Form coloured compounds
Behave as catalysts

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2
Q

what does variable oxidisation states mean

A

transition elements can form more than one positive ion

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3
Q

when transition metals form ions from which orbital do they lose electrons from first

A

4s subshell first

This is because when the orbitals are occupied, the repulsion between electrons pushes the 4s into a higher energy state so that it now becomes slightly higher in energy than the 3d subshell

The 4s is now the outer shell and loses electrons first

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4
Q

what complexes can transition element ions form

A

complexes which consist of a central metal ion and ligands

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5
Q

what is a ligand

A

(A ligand is a) molecule or (negative) ion with a (lone) pair (of electrons)
ALLOW
Species / Compound / group
(1)

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6
Q

what is a co -ordination number

A

number of dative bonds formed between the central metal ion and the ligands

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7
Q

what does the overall charge on the complex ion equal to

what does the overall charge equal to if ligands are neutral

A

The overall charge on the complex ion is the sum of the oxidation states of all the species present

If the ligands are neutral then the overall charge will be the same as the oxidation state of the metal ion

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8
Q

what is the nomenclature of complexes

A

Prefix for number of ligands/ligand name/element/oxidation number

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9
Q

what is different when naming complexes if the overall ion is an anion

A

the name of element is modified to have the name ending ‘ate’

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10
Q

what prefix does ammonia take

A

ammine as a ligand

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11
Q

why do most transition metal compounds appear coloured

A

This is because they absorb energy corresponding to certain parts of the visible electromagnetic spectrum

The colour that is seen is made up of the parts of the visible spectrum that aren’t absorbed

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12
Q

what colours are absorbed

A

The colours absorbed are complementary to the colour observed

Complementary colours are any two colours which are directly opposite each other in the colour wheel

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13
Q

why type of ions are not coloured

A

Ions that have completely filled 3d energy levels (such as Zn2+) and ions that have no electrons in their 3d subshells (such as Sc3+) are not coloured

Transition metals have a partially filled 3d energy level

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14
Q

what happens when ligands attach to central metal ions

A

the energy level splits into two levels with slightly different energies

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15
Q

what is promotion / excitation

A

If one of the electrons in the lower energy level absorbs energy from the visible spectrum it can move to the higher energy level

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16
Q

what does the amount of energy absorbed depend on

A

difference between the energy levels
A larger energy difference means the electron absorbs more energy

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17
Q

what is the amount of energy gained by the electron directly proportional to and inversely proportional to

A

The amount of energy gained by the electron is directly proportional to the frequency of the absorbed light and inversely proportional to the wavelength

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18
Q

what is the size of the splitting energy in the d-orbitals dependant on

A

The size and type of ligands
The nuclear charge and identity of the metal ion
The oxidation state of the metal
The shape of the complex

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19
Q

how does the size and type of ligand influence the splitting energy size

A

Ligands vary in their charge density
The greater the charge density; the more strongly the ligand interacts with the metal ion causing greater splitting of the d-orbitals

The greater the splitting, the more energy is needed to promote an electron to the higher group of orbitals

Therefore, the further it is shifted towards the region of the spectrum where it absorbs higher energy

As splitting increases, the light absorbed will shift away from the red end of the spectrum (longer wavelengths), towards the yellow end (shorter wavelengths)

As a result, a different colour of light is absorbed by the complex solution and a different complementary colour is observed

This means that complexes with the same transition elements ions, but different ligands, can have different colours

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20
Q

how does oxidation number influence the size of the splitting energy in d-orbitals

A

When the same metal has a higher oxidation number that will also create a stronger interaction with the ligands

If you compare iron(II) and iron (III):
[Fe(H2O)6]2+ absorbs in the red region and appears green
But, [Fe(H2O)6]3+ absorbs in blue region and appears orange

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21
Q

how does coordination number influence the size of the splitting energy in d-orbitals

A

The change of colour in a complex is also partly due to the change in coordination number and geometry of the complex ion

The splitting energy, ΔE, of the d-orbitals is affected by the relative orientation of the ligand as well as the d-orbitals

Changing the coordination number generally involves changing the ligand as well, so it is a combination of these factors that alters the strength of the interactions

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22
Q

when are octahedral complexes formed

A

Octahedral complexes are formed when a central metal atom or ion forms six coordinate bonds

This could be six coordinate bonds with six small, monodentate ligands or It could be six-coordinate bonds with three bidentate ligands

It could be six-coordinate bonds with one multidentate ligand

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23
Q

what are the bond angles in octahedral complexes

A

The bond angles in an octahedral complex are 90°

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24
Q

what is a tetrahedral complex

A

When there are four coordinate bonds

25
Q

what is the bond angle in tetrahedral complexes

A

109.5°

26
Q

what is a square planar geometry

A

complexes with four coordinate bonds may adopt a square planar geometry instead of a tetrahedral one

Cyanide ions (CN-) are the most common ligands to adopt this geometry

27
Q

bond angle in square planar complex

A

90 degrees

28
Q

what does cis platin look like

A

two Cl’s on the left
two NH3 on the right

29
Q

what does cis-platin do

A

cis platin pass through cell membrane
chlorine ligands substituted by water ligands then water ligands are removed to allow dative covalent bonding of cis plating with nitrogen bases in dna which distrups dna structre and prevents replication and dividing

30
Q

drawback of cis-platin

A

binds to healthy cells as well as cancerous cells, but affects cancer cells more as they are replicating faster
Unfortunately, this means that other healthy cells which replicate quickly, such as hair follicles, are also affected by cis-platin

31
Q

what is the metal ion in the centre of haem molecule

A

The haem molecule is a complex with iron(II) at its centre

32
Q

what does haemoglobin complex contain

A

a multidentate ligand made up of four haem groups

These consist of mostly carbon and hydrogen atoms

Each haem group has a nitrogen atom forming a dative covalent bond to the Fe2+ ion in a square planar complex

There is a fifth dative bond from the protein (globin) to the Fe2+ ion

Oxygen atoms form a dative covalent bond with the iron(II) which enables oxygen molecules to be transported around the body in the blood

33
Q

what does it mean that oxygen molecules are not very good ligands

A

Oxygen molecules are not very good ligands and bond weakly to the iron(II)
The weak bonds allows them to break off easily and be transported into cells

34
Q

why is carbon monoxide toxic

A

because it is a better ligand than oxygen and binds strongly and irreversibly to the iron(II) preventing oxygen from being carried to the cells

35
Q

what happens if oxygen attached to the haemoglobin is replaces by carbon monoxide

A

a darker red colour is produced in the haem complex
A sign of carbon monoxide poisoning
The condition anaemia occurs when a person does not have enough haemoglobin in their blood due to a loss of blood or deficiency in iron

36
Q

how can deficiency in iron be restored

A

by taking iron sulfate tablets

37
Q

what enables transition metals to catalyse certain redox

A

The ability of transition metals to form more than one stable oxidation state means that they can accept and lose electrons easily

38
Q

what is a heterogeneous catalyst

A

A heterogeneous catalyst is in a different physical state (phase) from the reactants

Heterogeneous catalysts are usually solids whereas the reactants are gaseous or in solution

The reaction occurs at active sites on the surface of the catalyst

39
Q

what is a homogeneous catalyst

A

A homogeneous catalyst is in the same physical state (phase) as the reactants

40
Q

what is surface adsorption theory

A

This theory can be used to explain how a heterogeneous catalyst works

Adsorption, in which one or more reactants becomes attached to the surface of the catalyst

Reaction, following the weakening of the bonds in the adsorbed reactants

Desorption, in which the reaction product becomes detached from the surface of the catalyst

Adsorption of reactants at active sites on the surface may lead to catalytic action

The active site is the place where the reactants adsorb onto the surface of the catalyst

This can result in the bonds within the reactant molecules becoming weaker, or the molecules being held in a more reactive configuration

There will also be a higher concentration of reactants at the solid surface so leading to a higher collision frequency

41
Q

what does the strength of the adsorption help to determine

A

The strength of adsorption helps to determine the effectiveness of the catalytic activity

Some metals e.g. W have too strong adsorption and so the products cannot be released

Some metals e.g. Ag have too weak adsorption, and the reactants do not adsorb in high enough concentration

42
Q

what does increasing surface area of solid catalyst improve

A

increasing the surface area of a solid catalyst will improve its effectiveness.

A support medium is often used to maximise the surface area and minimise the cost

43
Q

what are the advantages of heterogeneous catalyst

A

can be filtered off and are easy to separate from any liquid or gaseous products

They are also suited to continuous processes rather than batch processes

44
Q

steps of contact process

A

The first step of the process is roasting sulfur in air to produce sulfur dioxide

S (s) + O2 (g) → SO2 (g)

The second step is an equilibrium reaction which is catalysed by vanadium(V) oxide, V2O5,

2SO2 (g) + O2 (g) ⇌ 2SO3(g)

The vanadium(V) oxide catalyst converts sulfur dioxide into sulfur trioxide and is reduced to vanadium(IV) oxide
The oxidation number of the vanadium decreases from +5 to +4

SO2 (g) + V2O5 (s) → V2O4 (s) + SO3 (g)

The vanadium(V) oxide is then re-generated by reaction with oxygen, fulfilling its role as a catalyst
The original catalyst is regenerated as the oxidation number of vanadium increases from +4 to its original value of +5

O2 (g) + 2V2O4 (s) → 2V2O5 (s)

45
Q

what are catalytic converters used for and what do they contain

A

used in car exhaust boxes to reduce air pollution.

They usually consist of a mixture of finely divided platinum and rhodium supported on a ceramic base

46
Q

what do transition metal catalyst facilitate the conversion of in catalytic converters

A

CH3CH2CH3 (g) + 5O2 (g) → 3CO2 (g) + 4H2O (g)

2NO (g) + 2CO (g) → N2 (g) + 2CO2 (g)

47
Q

2NO (g) + 2CO (g) → N2 (g) + 2CO2 (g)

describe using surface adsorption theory

A

Molecules of carbon monoxide and nitrogen monoxide are absorbed onto the surface

The bonds in both molecules are weakened causing them to react together to form carbon dioxide and nitrogen

The products are then desorbed from the surface of the catalyst

48
Q

how can you minimise the cost and maximise the efficiency of the catalyst

A

Increasing the surface area of the catalyst

Coating an inert surface medium with the catalyst to avoid using large amounts of the catalyst

This is achieved by spreading the catalyst over a hollow matrix such as a honeycomb-like structure

49
Q

what is the key feature of homogeneous catalysis

A

formation of an intermediate species for which a specific formula can be written

50
Q

transition element ions can adopt more than one stable oxidation state explain what this means

A

This means that they can accept and lose electrons easily to go from one oxidation state to another

They can therefore catalyse redox reactions, by acting as both oxidising agents and reducing agents

51
Q

what is autocatalysis

A

term used to describe a reaction which is speeded up by a product which acts as a catalyst for the reaction

52
Q

when overall ion is an anion how is the element named

A

the name of element is modified to have the name ending ‘ate’

tetrachlorcuprate(II)
hexaaquairon(II)
hexaamminecobalt(II)
tetracyanonickelate

53
Q

what prefix does ammonia take as a ligand

A

Ammonia takes the prefix ammine as a ligand, which is spelt with a double ‘m’ unlike the functional group amine

54
Q

explain why [Co(H2O)6]2+ is coloured (pink)

A

Splitting
* (ligand / water molecule causes) d orbitals to split (into 2 energy
levels) (1)

Absorption
* electrons absorb energy (in the visible region) / photons (of visible light) (1)

Promotion
* to promote electrons (to higher d orbitals) or
electrons move from lower to higher energy (d) orbitals / levels
(1)

Colour
the remaining light / unabsorbed light / complementary
colour / pink light is transmitted

55
Q

why are dry crystals of ammonium cobalt (II) sulfate

rinsed with ice cold water
placed in warm oven

A

ice cold water prevents ammonium cobalt (II) sulfate from redissolving

warm oven ensures water of crystallisation is not removed during drying

56
Q

what happens when ammonia is added to copper (II) sulfate

A

(blue solution initially forms pale)
blue precipitate Cu(OH)2
(1)

(which dissolves to) form dark/deep/royal blue solution [Cu(NH3)4]2+
(1)

57
Q

what is the number of H2O produced and substituted the same as

A

value of the charge on the ion

58
Q

What are the observations with sodium hydroxide is added drop by drop until in excess to a solution of chromium (III) ions

A

Green precipitate that dissolves in NaOH to form green solution

59
Q

When comparing complex ion formed with two different types of ligands what do you compare and contrast

A

Do they both form dative bonds
Coordination number
Octahedral/ tetrahedral
Bidendate / Hexadendate
Anionic or cationic depending on charge of ligands

60
Q

three characteristics of transition metals

A

catalytic properties
coloured ion
complex ion

61
Q
A

Chem Mock (34 decks)

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