Ch5.3 Transition elements Flashcards
Which 2 elements are exceptions to the Aufbau principle?
chromium and copper
How is chromium an exception to the Aufbau principle?
- 3d and 4s orbitals all contain 1 unpaired e-
- 1s2 2s2 2p6 3s2 3p6 4s1 3d5
How is copper an exception to the Aufbau principle?
- 3d orbital is filled completely leaving 4s half-filled
- 1s2 2s2 2p6 3s2 3p6 4s1 3d10
Which electrons are lost first when ions are formed of the transition elements and why?
- 4s electrons are lost before the 3d electrons unlike in all other elements
- this is because, once filled, the 4s electrons have a slightly higher energy than the 3d electrons
Define transition metal
a d block element that has an incomplete d-subshell as a stable ion
What are the physical properties of transition metals?
- high density
- high melting and boiling points
- shiny in appearance (lustrous)
- conduct electricity
What are the chemical properties of transition metals?
- have variable oxidation states
- transition metal compounds form coloured solutions in water
- catalysts
Can transition metals form ions with more than one stable oxidation state?
Yes
- all of the transition metals in period 4 do this (Ti to Cu)
Which compounds containing transition metals can act as strong oxidising agents?
- compounds containing a transition metal in a high oxidation state
eg. potassium manganate (VII) KMnO4
eg. potassium dichromate (VI)
K2Cr2O7
Explain what is meant by the statement: compounds of transition metals can undergo disproportionation
- the transition metal species is both oxidised and reduced in the same reaction
Explain why transition metal compounds are often coloured
- white light hits an object and part of the spectrum is absored by the object and the remaining is reflected which is the light we see
- as light hits a transition metal ion, the electrons become excited (energised) and if there are some partially filled d sub-shells available, they can move up an energy level
- as the electrons then drop back down, they release light energy which we see as colour
NOTE: a compound will only be coloured if the transition metal ion has partially filled d subshells
Define catalyst
- a substance which speeds up a reaction by providing an alternative pathway with a lower activation energy and isn’t used up itself in the reaction
Why are transition metals good catalysts?
- reactants are ADsorbed to the surface of a transition metal where it may gain or lose electrons and form an intermediate allowing a pathway with a lower activation energy
- the transition metals can vary in oxidation states and once the reaction has occurred, the products are DEsorbed and the transition metal remains unchanged
What is the equation for hydrogen production?
Zn(s) + H2SO4(aq) –> ZnSO4(aq) + H2(g)
What is the catalyst for the reaction for hydrogen production?
CuSO4 or Cu2+ ion
What is the equation for the contact process?
2SO2 + O2 ⇌ 2SO3
What is the catalyst for the reaction of the contact process?
V2O5 or V5+ ion
What is the equation for oxygen production?
2H2O2 –> 2H20 + O2
What is the catalyst for the reaction for oxygen production?
MnO2 or Mn4+ ion
What is the equation for the Haber process?
N2 + 3H2 ⇌ 2NH3
What is the equation for the hydrogenation of ethene?
C2H4 + H2 –> C2H6
What is the catalyst for a catalytic converter?
Pt or Pd
What is the catalyst for vitamin B12?
Co
Define ligand
a molecule or ion that can donate a pair of electrons to the central transition metal ion to form a coordinate bond (dative covalent bond)
Define coordinate bond
a bond in which one of the bonded atoms provides both electrons for the covalent bond
State some features of ligands
- all ligands have at least one lone pair of electrons
- ligands can be neutral molecules or charged
What is a monodentate ligand?
- a ligand that donates just one pair of electrons to the central metal ion to form one coordinate bond
- eg. Cl- , OH- , CN- , NH3 , OH2 , SCN- (thiocyanate)
What is a bidentate ligand?
- a ligand that contains 2 atoms which donate a pair of electrons each to the central metal ion
- 2 coordinate bonds are formed per ligand
What is a multidentate ligand?
- a ligand that can form several coordinate bonds
- eg. EDTA 4- (ethylenediaminetetraacetic acid)
Describe a linear complex ion giving its bond angles and occurrence
- 2 bonding regions in straight line
- angle 180 degrees
- occurs in Ag+ complexes
Describe a tetrahedral complex ion giving its bond angles and occurrence
- 4 bonding regions spread as far apart as possible
- angle 109.5 degrees
- occurs with large ligands eg. Cl-
Describe a square planar complex ion giving its bond angles and occurrence
- 4 bonding regions spread as far apart as possible in a planar restriction
- angle 90 degrees
- occurs in Pt 2+ complexes
Describe an octahedral complex ion giving its bond angles and occurrence
- 6 bonding regions spread as far as possible
- angle 90 degrees
- most common occurrence
What are the 2 types of stereoisomerism?
- cis-trans / E-Z
- optical isomerism
What is stereoisomerism?
molecules or complexes with the same structural formula but with a different spatial arrangement of these atoms
What is cis-platin and how does it work?
- a very effective drug to fight cancer
- it works by binding to DNA and stopping replication and cell division
What is optical isomerism?
- optical isomers are non-superimposable mirror images of each other
What do ligand substitution reactions involve?
- a ligand in a complex ion being removed and replaced by another ligand
- common ligand substitution reactions involve the substitution of water molecules with another ligand
[Cu(H2O)6]2+ + NH3 (dropwise)
equation, colours, type of reaction
[Cu(H2O)6]2+ + 2NH3 –> [Cu(H2O)4(OH)2] + 2NH4+
[Cu(H2O)6]2+ is pale blue solution
[Cu(H2O)4(OH)2] is pale blue precipitate
hydrolysis reaction
ammonia acts as a base pulling a proton off two of the water ligands
[Cu(H2O)4(OH)2] + NH3 (excess after dropwise)
equation, colours, type of reaction
[Cu(H2O)4(OH)2] + 4NH3 –> [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH-
[Cu(H2O)4(OH)2] is a pale blue precipitate
[Cu(H2O)2(NH3)4]2+ is a deep blue solution
substitution reaction
adding NH3 in excess causes ligand exchange to occur
[Cu(H2O)6]2+ + NH3 (excess straight away/overall reaction)
equation, colours, type of reaction
[Cu(H2O)6]2+ + 4NH3 ⇌ [Cu(H2O)2(NH3)4]2+ + 4H2O
[Cu(H2O)6]2+ is a pale blue solutiion
[Cu(H2O)2(NH3)4]2+ is a deep blue solution
substitution reaction
[Cr(H2O)6]3+ + NH3 (dropwise)
equation, colours, type of reaction
[Cr(H2O)6]3+ + 3NH3 –> [Cr(H2O)3(OH)3] + 3NH4+
[Cr(H2O)6]3+ is a pale purple solution but can look green due to impurities
[Cr(H2O)3(OH)3] is a dark green precipitate
hydrolysis reaction
ammonia is acting as a base when it pulls protons from 3 of the water ligands
[Cr(H2O)3(OH)3] + NH3 (excess after dropwise)
equation, colours, type of reaction
[Cr(H2O)3(OH)3] + 6NH3 –> [Cr(NH3)6]3+ + 3H2O + 3OH-
[Cr(H2O)3(OH)3] is a dark green precipitate
[Cr(NH3)6]3+ is a purple solution
substitution reaction
(more likely to occur with conc NH3)
[Cr(H2O)6]3+ + 6NH3 (excess straight away/overall reaction)
equation, colours, type of reaction
[Cr(H2O)6]3+ + 6NH3 ⇌ [Cr(NH3)6]3+ + 6H2O
[Cr(H2O)6]3+ is a pale purple solution but can look green due to impurities
[Cr(NH3)6]3+ is a purple solution
substitution reaction
[Cu(H2O)6]2+ + conc HCl
equation, colours, type of reaction
[Cu(H2O)6]2+ + 4Cl- ⇌ [CuCl4]2- + 6H2O
OR
[Cu(H2O)6]2+ + HCl ⇌ [CuCl4]2- + 6H2O + 4H+
[Cu(H2O)6]2+ is a pale blue solution
[CuCl4]2- is a yellow solution
(often looks green instead of yellow because there is a mix of the blue and yellow solutions present)
[Cu(H2O)6]2+ + NaOH (dropwise vs excess)
equation, colours, type of reaction
dropwise full equation
[Cu(H2O)6]2+ + 2OH- –> [Cu(H2O)4(OH)2] +2H2O
dropwise simple equation
Cu2+ + 2OH- –> Cu(OH)2
excess: no further reaction
[Cu(H2O)6]2+ is a pale blue solution
[Cu(H2O)4(OH)2] / Cu(OH)2 is a blue gelatinous precipitate
hydrolysis reaction
[Fe(H2O)6]2+ + NaOH (dropwise vs excess)
equation, colours, type of reaction
dropwise full equation [Fe(H2O)6]2+ + 2OH- –> [Fe(H2O)4(OH)2] + 2H2O
dropwise simple equation
Fe2+ + 2OH- –> Fe(OH)2
excess: no further reaction but precipitate darkens in time on the surface as it oxidises to [Fe(H2O)3(OH)3] (orange-brown precipitate)
[Fe(H2O)6]2+ is a pale green solution
[Fe(H2O)4(OH)2] / Fe(OH)2 is a dark green precipitate
hydrolysis reaction
[Fe(H2O)6]2+ + NH3 (dropwise vs excess)
equation, colours, type of reaction
dropwise
[Fe(H2O)6]2+ + 2NH3 –> [Fe(H2O)4(OH)2] + 2NH4+
excess: no further reaction but the precipitate darkens with time on oxidation to [Fe(H2O)3(OH)3]
[Fe(H2O)6]2+ is a pale green solution
[Fe(H2O)4(OH)2] is a dark green precipitate
hydrolysis reaction
[Fe(H2O)6]3+ + NaOH (dropwise vs excess)
equation, colours, type of reaction
dropwise full equation
[Fe(H2O)6]3+ + 3OH- –> [Fe(H2O)3(OH)3] + 3H2O
dropwise simple equation
Fe3+ + 3OH- –> Fe(OH)3
excess: no further reaction
[Fe(H2O)6]3+ is a pale yellow solution
[Fe(H2O)3(OH)3] is an orange-brown precipitate
hydrolysis reaction
[Fe(H2O)6]3+ + NH3 (dropwise vs excess)
equation, colours, type of reaction
dropwise
[Fe(H2O)6]3+ + 3NH3 –> [Fe(H2O)3(OH)3] + 3NH4+
excess: no further reaction
[Fe(H2O)6]3+ is a pale yellow solution
[Fe(H2O)3(OH)3] is an orange-brown precipitate
hydrolysis reaction
[Mn(H2O)6]2+ + NaOH (dropwise vs excess)
equation, colours, type of reaction
dropwise full equation
[Mn(H2O)6]2+ + 2OH- –> [Mn(H2O)4(OH)2] + 2H2O
dropwise simple equation
Mn2+ + 2OH- –> Mn(OH)2
excess:
no further reaction but the precipitate darkens over time as it oxidises:
4Mn(OH)2 + O2 –> 2Mn2O3 + H2O
[Mn(H2O)6]2+ is a very pale pink solution
[Mn(H2O)4(OH)2] is a brown precipitate
hydrolysis reaction
[Mn(H2O)6]2+ + NH3 (dropwise vs excess)
equation, colours, type of reaction
dropwise
[Mn(H2O)6]2+ + 2NH3 –> [Mn(OH)2(H2O)4] + 2NH4+
excess:
no further reaction but the precipitate darkens over time as it oxidises:
4Mn(OH)2 + O2 –> 2Mn2O3 + H2O
[Mn(H2O)6]2+ is a very pale pink solution
[Mn(H2O)4(OH)2] is a brown precipitate
hydrolysis reaction
[Cr(H2O)6]3+ + NaOH (dropwise)
equation, colours, type of reaction
[Cr(H2O)6]3+ + 3OH- –> [Cr(H2O)3(OH)3] + 3H2O
[Cr(H2O)6]3+ is a pale purple solution but can look green due to impurities
[Cr(H2O)3(OH)3] is a dark green precipitate
hydrolysis reaction
[Cr(H2O)3(OH)3] + NaOH (excess after dropwise)
equation, colours, type of reaction
precipitate re-dissolves in excess hydroxide
[Cr(H2O)3(OH)3] + 3OH- –> [Cr(OH)6]3- + 3H2O
[Cr(H2O)3(OH)3] is a dark green precipitate
[Cr(OH)6]3- is a dark green solution
substitution reaction
What is the test for ammonium ions?
- add NaOH to NH4+ sample to make NH3 and H2O
- NH3 will turn damp red litmus paper blue
What is the test for carbonate ions?
- add HCl to sample
CO3 2- + 2H+ –> H2O + CO2
CO2 turns limewater cloudy when it’s bubbled through
What is the test for sulphate ions?
- add HCl followed by BaCl2
Ba2+ + SO4 2- –> BaSO4
BaSO4 is a white precipitate
What is the test for halide ions?
- add nitric acid followed by silver nitrate
AgCl, AgBr or AgI formed
AgCl is white precipitate that dissolves in dilute or conc ammonia
AgBr is a cream precipitate that dissolves in just conc ammonia
AgI is a yellow precipitate that is insoluble in ammonia of any conc
How does haemoglobin relate to ligand substituution?
- haemoglobin is a complex protein of 4 polypeptide chains and each haemoglobin has 4 haem groups
- each haem group has an Fe2+ ion at its centre, oxygen can reversibly bind to the Fe2+ ion which allows oxygen to be transported around the body
Describe the stucture of the Fe2+ complex ion in haemoglobin
- there are 4 coordinate bonds between the Fe2+ ion and the nitrogen atoms in the haem structure
- a further coordinate bond is formed with globin protein
- the final coordinate bond is formed with an O2 molecule which is then transported
Describe and explain how CO is related to haemoglobin and ligand substitution
- CO and O2 can both bind to haemoglobin at the same place
- CO binds more strongly to the haemoglobin than O2
- if CO and O2 are both present in the lungs then CO will bind over O2 so there is less haemoglobin for O2 to bind to
- CO molecules can replace O2 molecules and they are both ligands so this is ligand substitution
- reaction of binding isn’t reversible for CO
What happens to the body if CO and O2 are both present in the lungs at the same time?
- tissues are starved of O2 because it can’t be transported
What symptoms can different concentrations of CO in the blood cause?
- low concs: headaches, nausea and potential suffocation
- high concs: fatal
How is CO formed?
- during incomplete combustion of carbon-containing fuels
- burning tobacco also releases CO which is why long-term smokers become short of breath
What are the physical properties of CO?
- colourless
- odourless
