Complex: central metal atom / ion surrounded by ligands
Ligand: A species which can use its lone pair to form a dative covalent bond to a transition metal.
Co-ordination number: Number of co-ordinate bonds to the central metal atom/ion
What shape is formed with a co-ordination number of 6?
Octahedral
Small ligands e.g H2O and NH3
What types of ligands are there?
monodentate = attach with 1 co-ordinate
bondbidentate = attach with 2 co-ordinate bonds from two atoms (each donate lone pair)
multidentate = attach with multiple co-ordiinate bonds
What type of isomerism do square planar complexes display? Geometric isomerism
How can transition metals be identified? by their colour
Which acid do you use for redox if you want to reduce a species? HCl provides H+ for reduction
Acid to use for redox if you want to oxidise a species:
Use H2SO4 to provide H+ for oxidation
What is the effect of pH on redox in transition metals? Reduction favoured by acidic conditions
Bidentate ligand: Coordinatebonds from two atoms
Transition metals and their compounds can act as hetereogenous and homogenous catalysts
V2O5 and Fe are examples of heterogenous catalysts
Catalyst poisoning:
Impurities can block active sites
so the have reduced efficiency
What can act as a poison in the Haber process? sulphur
What can act as a poison in a catalytic converter? Lead
Haem: An iron (II) complex with a multidentate ligand.
CO is toxic because it replaces O2 co-ordinately bonded to Fe (II) in haemoglobin.
This prevents Hb from transporting O2
Chelate effect: Bidentate and multidentate ligands replace monodentate ligands from complexes - resulting in a more stable complex.
W is a bad catalyst because it's adsorption is too strong
Ag is a a bad catalyst because
adsorbtion is too weak and reactants do not absorb in high enough concentrations
Transition element: An element which forms at least one stable ion with a partially full d-shell of electrons
Where are the transition metals located in the periodic table? In the middle (block from Ti to Cu) - part of the d-block
What are some characteristic physical properties of transition metals?
Metallic
good conductors of heat and electricity
hard, strong, shiny
high m.p., high b.p., low reactivity.
What are the characteristic chemical properties of transition metals:
Variableoxidation states → take part in many redox reactions
Coloured compounds/ions in solution
Good catalysts
Form complex ions
Catalysts are usually spread over an inert support medium to
Increase surface area
Reduce cost
Which electrons do transition metals lose first when forming ions? 4s
mono/unidentate ligands: A ligand that forms one co-ordinate bond to the central metal ion (one lone pair to donate)
Give some examples of common monodentate ligands: Cl- , H2O, NH3 , CN
How many co-ordinate bonds does EDTA4- form? six
Define the term coordination number: The number of co-ordinate bonds the metal ion has formed to surrounding ligands
Chelate effect: Chelate complexes with multidentate ligands are favoured over monodentate ligands or ligands that form fewer co-ordinate bonds per molecule
If a transition metal ion has 2 ligands, what shape is it usually? Linear
If a transition metal ion has 4 ligands, what shape is it usually? Tetrahedral
What shape is a complex ion if it has 6 ligands? Octahedral
What conditions are needed for a complex ion display to optical isomerism? Usually applies to octahedral molecules with 2 or more bidentate ligands, so that the mirror images are non-superimposable
What affects the colour of a transition metal compound?
ΔE affects the frequency of absorbed photons, so determines the colour
ΔE is changed by oxidation state of the metal, number and type of ligands, shape, co-ordination number