principle of transition metals Flashcards
what is a transition metal
elements with an incomplete d-subshell that can form at least one stable ion with an incomplete d-subshell
what are general properties of transition elements
Variable oxidation states
Form complex ions
Form coloured compounds
Behave as catalysts
what does variable oxidisation states mean
transition elements can form more than one positive ion
when transition metals form ions from which orbital do they lose electrons from first
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
what complexes can transition element ions form
complexes which consist of a central metal ion and ligands
what is a ligand
(A ligand is a) molecule or (negative) ion with a (lone) pair (of electrons)
ALLOW
Species / Compound / group
(1)
what is a co -ordination number
number of dative bonds formed between the central metal ion and the ligands
what does the overall charge on the complex ion equal to
what does the overall charge equal to if ligands are neutral
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
what is the nomenclature of complexes
Prefix for number of ligands/ligand name/element/oxidation number
what is different when naming complexes if the overall ion is an anion
the name of element is modified to have the name ending ‘ate’
what prefix does ammonia take
ammine as a ligand
why do most transition metal compounds appear coloured
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
what colours are absorbed
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
why type of ions are not coloured
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
what happens when ligands attach to central metal ions
the energy level splits into two levels with slightly different energies
what is promotion / excitation
If one of the electrons in the lower energy level absorbs energy from the visible spectrum it can move to the higher energy level
what does the amount of energy absorbed depend on
difference between the energy levels
A larger energy difference means the electron absorbs more energy
what is the amount of energy gained by the electron directly proportional to and inversely proportional to
The amount of energy gained by the electron is directly proportional to the frequency of the absorbed light and inversely proportional to the wavelength
what is the size of the splitting energy in the d-orbitals dependant on
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
how does the size and type of ligand influence the splitting energy size
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
how does oxidation number influence the size of the splitting energy in d-orbitals
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
how does coordination number influence the size of the splitting energy in d-orbitals
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
when are octahedral complexes formed
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
what are the bond angles in octahedral complexes
The bond angles in an octahedral complex are 90°
what is a tetrahedral complex
When there are four coordinate bonds
what is the bond angle in tetrahedral complexes
109.5°
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
bond angle in square planar complex
90 degrees
what does cis platin look like
two Cl’s on the left
two NH3 on the right
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
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
what is the metal ion in the centre of haem molecule
The haem molecule is a complex with iron(II) at its centre
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
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
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
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
how can deficiency in iron be restored
by taking iron sulfate tablets
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
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
what is a homogeneous catalyst
A homogeneous catalyst is in the same physical state (phase) as the reactants
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
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
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
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
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)
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
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)
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
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
what is the key feature of homogeneous catalysis
formation of an intermediate species for which a specific formula can be written
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
what is autocatalysis
term used to describe a reaction which is speeded up by a product which acts as a catalyst for the reaction
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
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
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
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
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)
what is the number of H2O produced and substituted the same as
value of the charge on the ion
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
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
three characteristics of transition metals
catalytic properties
coloured ion
complex ion
