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principle of transition metals Flashcards

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
what is a tetrahedral complex
When there are four coordinate bonds
25
what is the bond angle in tetrahedral complexes
109.5°
26
what is a square planar geometry
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
bond angle in square planar complex
90 degrees
28
what does cis platin look like
two Cl's on the left two NH3 on the right
29
what does cis-platin do
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
drawback of cis-platin
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
what is the metal ion in the centre of haem molecule
The haem molecule is a complex with iron(II) at its centre
32
what does haemoglobin complex contain
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
what does it mean that oxygen molecules are not very good ligands
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
why is carbon monoxide toxic
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
what happens if oxygen attached to the haemoglobin is replaces by carbon monoxide
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
how can deficiency in iron be restored
by taking iron sulfate tablets
37
what enables transition metals to catalyse certain redox
The ability of transition metals to form more than one stable oxidation state means that they can accept and lose electrons easily
38
what is a heterogeneous catalyst
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
what is a homogeneous catalyst
A homogeneous catalyst is in the same physical state (phase) as the reactants
40
what is surface adsorption theory
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
what does the strength of the adsorption help to determine
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
what does increasing surface area of solid catalyst improve
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
what are the advantages of heterogeneous catalyst
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
steps of contact process
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
what are catalytic converters used for and what do they contain
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
what do transition metal catalyst facilitate the conversion of in catalytic converters
CH3CH2CH3 (g) + 5O2 (g) → 3CO2 (g) + 4H2O (g) 2NO (g) + 2CO (g) → N2 (g) + 2CO2 (g)
47
2NO (g) + 2CO (g) → N2 (g) + 2CO2 (g) describe using surface adsorption theory
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
how can you minimise the cost and maximise the efficiency of the catalyst
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
what is the key feature of homogeneous catalysis
formation of an intermediate species for which a specific formula can be written
50
transition element ions can adopt more than one stable oxidation state explain what this means
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
what is autocatalysis
term used to describe a reaction which is speeded up by a product which acts as a catalyst for the reaction
52
when overall ion is an anion how is the element named
the name of element is modified to have the name ending 'ate' tetrachlorcuprate(II) hexaaquairon(II) hexaamminecobalt(II) tetracyanonickelate
53
what prefix does ammonia take as a ligand
Ammonia takes the prefix ammine as a ligand, which is spelt with a double 'm' unlike the functional group amine
54
explain why [Co(H2O)6]2+ is coloured (pink)
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
why are dry crystals of ammonium cobalt (II) sulfate rinsed with ice cold water placed in warm oven
ice cold water prevents ammonium cobalt (II) sulfate from redissolving warm oven ensures water of crystallisation is not removed during drying
56
what happens when ammonia is added to copper (II) sulfate
(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
what is the number of H2O produced and substituted the same as
value of the charge on the ion
58
What are the observations with sodium hydroxide is added drop by drop until in excess to a solution of chromium (III) ions
Green precipitate that dissolves in NaOH to form green solution
59
When comparing complex ion formed with two different types of ligands what do you compare and contrast
Do they both form dative bonds Coordination number Octahedral/ tetrahedral Bidendate / Hexadendate Anionic or cationic depending on charge of ligands
60
three characteristics of transition metals
catalytic properties coloured ion complex ion
61

Chem Mock (34 decks)

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