3.2.5 - Transition Metals Flashcards
Transition metals
Elements in the d-block of the periodic table with a partially filled d-orbital. They lose electrons to form positive ions with the s-orbital electrons being removed first
Physical properties of transition metals
Similar physical properties, atomic radius, high densities and high melting and boiling points
Chemical properties of transition metals
Form complexes, form coloured ions, variable oxidation states, good catalysts
Complexes
form from transition metals, consisting of a central metal ion or atom surrounded by ligands
Ligands
Molecules or ions with a lone electron pair that is able to form a coordinate bond to the central metal ions by donating this electron pair.
Common ligands
Cl-
H2O
NH3
Coordination number
Equal to the number of coordinate bonds formed around the central metal ion
Coordination number of silver complexes
2
Common coordination number of platinum complexes
4
Exchange between ligands NH3 and H2O
They can be exchanged without a change in coordination number via a ligand substitution reaction
Equation for ligand substitution reaction between NH3 and H2O ligands
[Co(H2O)6]2+ + 6NH3 –> [Co(NH3)6]2+ + 6H2O
Exchange between copper complexes and NH3 in excess
The substitution is incomplete and the complex formed has a combination of water and ammonia ligands
Equation for reaction between [Cu(H2O)6]2+ and NH3
[Cu(H2O)6]2+ + 4NH3 –> [Cu(H2O)2(NH3)4]2+ + 4H2O
colour of [Cu(H2O)2(NH3)4]2+
forms as a deep blue solution
Exchange between copper complexes and Cl-
Cl- ligand is much larger than NH3 and H2O ligands meaning substitution with this ligand results in a change in coordination number for that complex
Equation for reaction between [Cu(H2O)6]2+ and Cl-
[Cu(H2O)6]2+ + 4Cl- –> [CuCl4]2- + 6H2O
Complexes with just Cl- ligands always have…
a coordination number of 4, producing a tetrahedral shaped complex
Bidentate ligands
Able to form two coordinate bonds to the central metal ion as they have two lone electron pairs
Common bidentate ligands
Ethanedioate ions, ethane-1,2-diamine
Ethanedioate ions
a lone pair electron on two of the oxygen atoms
Ethane-1,2-diamine
a lone electron pair on each of the nitrogen atoms
Multidentate ligands
Able to form up to six coordinate bonds to the central metal ion as they have multiple lone electron pairs
Most common multidentate ligand
EDTA (ethylenediaminetetraacetic acid)
Equation for reaction between iron compound and EDTA
[Fe(H2O)6]3+ + EDTA4- –> [FeEDTA]-1 + 6H2O
Another common multidentate ligand is…
Haem that consists of six coordinate bonds around a central Fe2+ ion and its shape & structure allow it to transport oxygen
Carbon monoxide
toxic to humans as it replaces the oxygen in the haem complex thus preventing it from being transported around the body
The chelate effect
more moles on the right is achieved by substituting unidentate ligands with bidentate or multidentate ligands
Positive entropy change
favourable as it means a more stable complex is being formed, it is favourable to have more moles on the right than the left
Enthalpy change
very small as bonds being formed are very similar to the bonds that were broken
Octahedral complexes
transition metal complexes with H2O and NH3 ligands commonly for octahedral complexes, bond angle 90°
Cis-trans isomerism
shown by octahedral complexes with different types of unidentate ligands where ligands of the same type can be opposite or next to each other
trans isomer
has two of the same ligands opposite each other
cis isomer
has two of the same ligands next to each other
optical isomerism
shown by octahedral complexes with bidentate ligands where the two isomers are mirror images of each other
tetrahedral complexes
Form when complexes for with larger ligands e.g. Cl-, bond angle 109.5°. Can show optical isomerism
Square planar complexes
form in Platinum and Nickel complexes, 4 coordinate bonds, bond angle 90°
Linear complexes
form in silver complexes, 2 coordinate bonds, bond angle 180°
Cisplatin
cis isomer of square planar complex of platinum
Uses of cisplatin
cancer therapy drug
Observing colour of compounds
White light shines on a substance some wavelengths are absorbed but remaining are reflected & transmitted to the eye. These reflected wavelengths correspond to a specific colour which is observed
Electrons in the d-orbital…
exist in a series of energy states, when given energy they move from the ground state to the excited state. ∆E corresponds to a wavelength and frequency of light
Colorimetry
An analytical technique that uses the absorption of visible light to determine the concentration of coloured ions by measuring absorbance
Calibration graph
Produced by measuring solutions of known concentrations which can then be used to calibrate the colorimeter on a graph of relative absorbance against concentration
Oxidation state of Vanadium in VO_2+
+5
Ion colour of VO_2+
yellow
Oxidation state of Vanadium in VO^2+
+4
Ion colour of VO^2+
blue
Oxidation state of V3+
+3
Ion colour of V3+
green
Oxidation state of V2+
+2
Ion colour of V2+
violet
Conditions for ions to be reduced
acidic
Equation of reduction of VO_2+
2VO_2+ + 2e- + 4H+ –> 2VO^2+ + 2H2O
Conditions for ions to be oxidised
alkaline as they react with water to produce OH- ions
Equation for oxidation of VO^2+
VO^2+ + H2O –> VO_2+ + 2H+ + e-
[Ag(NH3)2]+ (Tollens Reagent) is reduced by…
aldehydes to form silver atoms
Equation for reduction of Tollens Reagent
RCHO + 2[Ag(NH3)2]+ + 3OH- –> RCOO- + 2Ag + 4NH3 + 2H2O
Heterogeneous catalyst
catalysts that are in a different phase to the species in the reaction
Variable oxidation states make transition metals…
Good catalysts, electrons are transferred to produce a reactive intermediate and speed up the reaction rate
Homogeneous catalyst
catalysts are in the same phase to the species in the reaction
Adsorption
A solid catalyst works adsorbed molecule onto an active site on the surface of the catalyst. These active sites increase the proximity of molecules and weaken covalent bonds in molecules
Catalyst poisoning
Heterogeneous catalysts can be poisoned by impurities which block active sites and prevent adsorption
Homogeneous catalysts work by…
combining with reactants to produce a reactive intermediate which changes reaction path, activation energy is lower
