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 central metal atom or ion surrounded by ligands
What is meant by the term coordination number?
the number of co-ordinate binds 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-
Why are some transition metals coloured?
some wavelengths of light are absorbed and the remaining are transmitted or reflected
What do blue compounds absorb and reflect?
absorbs all parts of the spectrum except from blue light which it reflects
What happens to d electrons when light is absorbed?
They gain energy and move from a ground state to an excited state
How do d electrons relax back to the ground state?
releasing thermal energy
What 2 equations give the energy difference between ground and excited states?
change in energy = hc/wavelength
change in energy = hv
What factors change the difference in energy?
- oxidation state
- coordination number
- ligand
Why are transition metal compounds coloured?
- incomplete d-subshells
- so electrons can move between orbitals
- in compounds, d-orbitals have slightly different energy levels
What can colorimetry be used to determine?
concentration of coloured ions
How is colorimetry carried out to find concentration of coloured ions?
1) series of dilutions, with known concentrations
2) find absorbance using colorimeter
3) plot graph of absorbance vs conc and draw line of best fit
4) find absorbance of unknown sample
5) use graph
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
