Chapter 23 - Transition Metals Flashcards
What are the common properties of metals
Conduct electricity and heat
Strong
Hard
Shiny
High MP and BP
What block are the transition metals in
d-block
What is a transition metal
It is a metal that forms at least 1 stable ion with a partially filled d-shell of electrons
What are the general properties of transition metals
Variable oxidation state
Catalysis
Complex Formation
Colour
What can transition metals form
Complex ions
How are complex ions formed
When a transition metal or ion becomes surrounded by ligands
The ligands form coordinate bonds by donating electron pairs
What are ligands
A cluster of molecules or ions that are bonded to the metal in a complex ion
Can be neutral or ionic
What is the coordination number
The number of bonds around the central metal atom or ion
What are examples of neutral ligands
H2O
NH3
CO
What are examples of ionic ligands
Cl-
OH-
CN-
In complex formations, what do the ligands function as
Lewis bases
What are Lewis Bases
Electron pair donors
What are Lewis acids
Electron pair acceptor
In complex formations, what does the transition metal act as
Lewis Acid
What are the 4 parts of the names of complexes
Prefix
Type of ligand
Name of metal
Oxidation number of metal
What are the prefixes of complexes
Hexa = 6 ligands
Tetra = 4 ligands
Di = 2 ligands
What are the examples of ligands
H2O = aqua
Cl- = chloro
NH3 = ammine
OH- = hydroxo
CN- = cyano
What are the names of metals for positively charged complexes
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
Silver
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
Silver
What are the names of metals for negatively charged complexes
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
Silver
Vanadate
Chromate
Manganate
Ferrate
Cobaltate
Nickelate
Cuprate
Zincate
Argentate
How are the oxidation number of the metal expressed
In roman numerals
What determines the shape of a complex
The coordination number
How are ligands classified
By the number of coordinate bonds they are able to form in complexes
What are the types of ligands
Unidentate
Bidentate
Multidentate
What are unidentate ligands
Ligands that bond through 1 donor atom
e.g. H2O, NH3, Cl-
What are bidentate ligands
Ligands that bond through 2 donor atoms
What are the 2 bidentate ligands
1,2 - diaminoethane (NH2 CH2 CH2 NH2)
ethanedioate ion (C2O4 2-)
What are multidentate ligands
Ligands that bond through many donor atoms
e.g. EDTA
What can complex ions exhibit
Geometric and optical isomerism
When can optical isomerism be displayed
Octahedral shape with 3 bidentate ligands
When can geometric isomerism (cis-trans isomerism) happen
Octahedral shape with 4 of the same ligand and 2 of a different ligand
Square planar with 2 ligands of the same and 2 different ligands
What is a compound with a square planar shape
Cisplatin
[Pt(NH3)2Cl2]
What type of geometric isomerism is Cis
The 2 different ligands are adjacent to each other
What type of geometric isomerism is trans
The 2 different ligands are opposite each other
How can chlorine atoms exist in complex salts
Chlorine ligands or free chloride ions
e.g. Cr(H2O)6 Cl3
How can you determine if a chlorine atom is in a complex or a free chloride ion
Silver Nitrate solution
Free chloride ions will form white silver chloride precipitate
Chlorine ligands won’t react
The number of moles of AgCl formed per mole of complex shows how many atoms of chlorine are free
What are chelates
They are complexes containing multidentate ligands
What is the order of ligands ability to bind from best to worst
Multidentate
Bidentate
Unidentate
What can transition metals form
coloured complexes
Why are transition metal complexes coloured
They are able to absorb visible light
The colour we observe depends on the wavelengths absorbed by the complex
What colour is the complex when a particular colour is absorbed
Its complementary colour is reflected
How are transition metals able to absorb light
When ligands surround the central ion it causes the d-orbitals to split into 2 slightly different energy levels
The electrons absorb energy in the visible region, they move from 1 d-orbital to a higher one
This causes a combination of the non absorbed colours to form the coloured compound
How is the energy absorbed found
(the difference between the lower and higher energy levels)
Using Planck’s equation
AE = hv
h= Planck’s constant
v=frequency of light absorbed
What affects the size of the energy gap
The transition metal
Type of ligand attached
Co-ordination number in the complex
Oxidation state of the transition metal
What does a colorimeter measure
The absorption of visible light
What can data from a colorimeter be used to do
Construct a calibration curve, measuring the absorbance of solutions of known concentration and then using this to find the concentration of unknown solution based on their absorbance
What is required sometimes for complexes with place colours
Might be necessary to add a different ligand to intensify the colour
What can colourmetry also be used for
Used to find the ratio of metal ions to ligand in a a complex
What are the 2 ways to do a colorimetry experiment to find concentration of unknown solutions
Keep the volume of the metal ion constant and adding different amounts of ligands
Varying the volume of both solutions but keep the final volume constant
What will happen in the experiment
When the volume of metal ion and ligand are mixed in the same ratio as they are in the complex, the absorbance will peak
What are the most common oxidation states of each transition metal
Ti
V
Cr
Fe
Co
Ni
Cu
Zn
Ti - 4
V - 4 and 5
Cr - 2,3 and 6
Fe - 2 and 3
Co - 2 and 3
Ni - 2
Cu - 2
Zn - 2
What do the lower oxidation states exist as
Simple ions
What do the higher oxidation states exist as
In compounds with very electronegative ions
What is reduction
Gain of electrons
What is a reducing agent
Loss of electrons
What is oxidation
Loss of electrons
What is an oxidising agent
Gains electrons
What does the ease of changing an oxidation state of a TM depend on
pH and the ligands present
What conditions is it easier to oxidise a transition metal
alkaline
What conditions is it easier to reduce a transitional metal
acidic
What is a catalyst
A substance which alters the rate of a chemical reaction but is unchanged at the end
How do catalysts work
They provide an alternative reaction route with a lower activation energy
What do catalysts not affect
AG
AH
position of equilibrium
Why can transition metals be used as catalysts
Their partially filled d-orbitals allow them to alternatively accept and reject electrons by changing oxidation states
This allows them to help transfer electrons
What are the 2 types of catalysts
Homogeneous
Heterogeneous
What are homogeneous catalysts
Where the catalyst is in the same phase
What are heterogeneous catalysts
Catalysts in a different phase to the reactants
What processes involve heterogeneous catalysis
Haber process
Contact process
Making methanol
How do heterogeneous catalysts work
They absorb reactants onto the surface of catalyst, forming weak bonds
Reaction occurs
The product molecules are desorbed from surface and diffuse away
How can the absorption of reactants increase the rate of reaction
Absorption concentrates the reactants, brings them closer
It may weaken bonds within the reactants
It may position the molecules in a favourable orientation
How are catalysts used efficiently
Increase surface area
Spreading the catalyst onto an inert support medium - increases surface to mass ratio
Why don’t catalysts last forever
The finely divided catalyst can simply come off the support medium
The catalyst becomes poisoned
What is catalyst poisoning
When the surface becomes covered with unwanted impurities blocking active sites
How is a catalyst used for the Haber process
Iron catalyst
N2 + 3H2 -> 2NH3
Becomes poisoned with sulphur
What is the contact process
It makes sulphuric acid
The key step is:
2SO2 + O2 -> 2SO3
Catalysed by Vanadium oxide
What are the 2 steps to catalyse the contact process
SO2 + V2O5 -> SO3 + V2O4
2V2O4 + O2 -> 2V2O5
What are the reaction for making methanol
CH4 + H2O -> CO + 3H2
It is manufactored from sythesis gas ( CO and H2)
CO + 2H2 -> CH3OH
Cr2O3 catalyst
How does homogeneous catalysts work
They can act as homogeneous catalysts for reactions in solution due to their variable oxidation number
This allows them to form intermediate species which have lower activation energy’s
What is the reaction between iodide and peroxodisulphate and how is it catalysted
2I- + S2O8 2- -> I2 + 2SO4 2-
Fe catalyst
S2O8 2- + 2Fe2+ -> 2SO4 2- + 2Fe3+
2Fe3+ + 2I- -> 2Fe2+ + I2
Why is the non-catalysed reaction of iodide with peroxodisulphate so slow
It involves the collision of 2 negatively charged ions
What is autocatalysis
It is where one of the products of a reaction is a catalyst for the reaction
What is the reaction of ethanedioate with manganate ions
2MnO4- + 16H+ + 5C2O4 2- -> 2Mn2+ + 10CO2 + 8H2O
What catalyst is there in the ethanedioate with manganate ions
Mn2+
What are the equations of the catalyst reacting with the reactants in the ethanedioate with manganate ions
MnO4- + 4Mn2+ + 8H+ -> 5Mn3+ + 4H2O
2Mn3+ + C2O4 2- -> 2Mn2+ + 2CO2
2MnO4- + 16H+ + 5C2O4 2- -> 2Mn2+ + 10CO2 + 8H2O
What is the reaction between chromate ions and iron 2+
Cr2O7 2- + 14H+ + 6Fe2+ -> 2Cr3+ + 7H2O + 6Fe3+
What is the reaction between manganate ions and iron 2+
MnO4- + 8H+ + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+
What is the equation for frequency of light
speed of light/wave length
Why in a calorimetry experiment does the container for each sample the same
Absorption depends on path length of light
