A2- Transition Metals Flashcards
What are 4 general properties of transition metals?
- form coloured ions
- form complexes
- variable oxidation states
- act as catalysts
What is a Ligand?
a species that can donate a pair of electrons to a central metal ion, forming a coordinate bond
What is meant by the term coordination number?
the number of co-ordinate bonds to the central metal atom or ion
What shape and bond angle does a complex with H2O ligands have?
Octahedral, 90
What shape and bond angle does a complex made with Cl have?
tetrahedral, 109.5
What is a bidentate ligand? give an example
a ligand that forms 2 coordinate bonds with the central metal atom
- diaminoethane
- ethanedioate
Why do transition metals share the same 4 general properties?
incomplete d-subshell
Why does Cl- form a tetrahedral complex?
larger ions
Give 3 examples of monodentate ligands
H2O, NH3, Cl-
What is a monodentate ligand?
a ligand that makes only one coordinate bond to the central metal ion or atom
Give an example of a multidentate ligand
EDTA4-
What are ligand substitution reactions?
reactions where ligands around a complex ion are substituted by other ligands
What is a complete ligand substitution with no change in coordination number?
a reaction where all ligands are substituted by new ones. Ligands must be a similar size
Why do complete ligand substitutions with no change in coordination number have small enthalpy changes?
small bond energies of ligands are similar
What is a complete ligand substitution with a change in coordination number?
a reaction where all ligands are substituted by new ones, ligands are different size
What is an incomplete ligand substitution with no change in coordination number?
only some ligands substituted but number of coordinate bonds stays the same
Why do multidentate ligands form thermodynamically stable compounds?
- very small enthalpy change as 6 C-O are broken and 6 are formed
- large entropy change as more species are produced
- very negative free energy change
Give an example of a Vanadyl (V) species…
What colour is this?
VO2 +
Yellow
Give an example of a Vanadyl (IV) species…
What colour is this?
VO 2+
Blue
Give an example of a Vanadium (III) species…
What colour is this?
V 3+
Green
Give an example of a Vanadium (II) species…
What colour is this?
V 2+
Purple
Why is +2 a common oxidation state?
2 electrons lost from 4s sub-shell
Which transition metal electron configurations are more stable than others?
those with a half-filled d sub-shell
How can Vanadium species be reduced?
heating with Zn metal
How can Vanadium species be oxidised?
oxidising agents such as manganate (VII) solution
What affects the redox potential of transition metals?
- pH
- type of ligands
- conditions (temp, pressure and conc)
What are redox titrations?
titrations based on change in oxidation states
Give the equation for the redox titration between Iron (II) and Manganate (VII)
5Fe2+ + MnO4- + 8H+ –> Mn2+ + Fe3+ + 4H2O
What colour change occurs in the redox titration between Iron (II) and Manganate (VII)?
colourless to pink
Give the equation for the redox titration between ethanedioate and Manganate (VII)
5C2O42- + 2MnO4- + 16H+ –> 10CO2 + 8H2O + 2Mn2+
What is the chelate effect?
complexes with multi-dentate ligands are favoured over complexes with monodentate ligands, due to the the large increase in entropy
Why can HCl NOT be used in the redox titration between Iron (II) and Manganate (VII)?
Cl- ions will be oxidised by the manganate ions
How do you convert from nm to m?
x 10-9
