Transition metals -5
- Created by: Shannon
- Created on: 02-03-15 10:37
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- Transition Metals
- Defintion
- An element which forms one or more ions with a partially filled d-orbital
- Exceptions
- Sc and Zn are not transition metals. This is because they form ions with either no electrons the d-orbital or full d-orbital
- Exceptions
- An element which forms one or more ions with a partially filled d-orbital
- Properties
- 1) They have many oxidation states - therefore can form many ions
- 2) They form coloured ions
- 3) They can form complex ions
- 4) They have the ability to act as catalysts
- Electron configurations
- '4s first rule' - the 4s orbital is the first to fill with electrons and therefore the first to empty of electrons
- Exceptions
- Cr and Cu have half filled 4s orbitals
- The resulting configuration is the most stable
- Energy needed to promote the electron vs inter-electron repulsion
- d-orbitals are more compact, therefore increased repulsions between electrons. d-orbitals less stable
- 4s higher in energy, but difficult to promote electron
- The resulting configuration is the most stable
- Cr and Cu have half filled 4s orbitals
- Exceptions
- The highest oxidation state of any transition metal will be the oxidation state that gives it an electron config the same as Ar
- e.g Co = [Ar] 3d74s2
- '4s first rule' - the 4s orbital is the first to fill with electrons and therefore the first to empty of electrons
- Complexes
- Ligands
- Donate 2 electrons to form a dative covalent bond
- Ligands can bond with 1 or more 'teeth'
- Unidentate
- Bidentate
- Multidentate
- Ligands can bond with 1 or more 'teeth'
- Donate 2 electrons to form a dative covalent bond
- Why do they form coloured complexes?
- d-orbitals are degenerate, but when a ligand approaches, the orbitals are either destabilised or stabilised
- A.K.A ligand field splitting
- Tetrahedral complexes
- Splitting occurs 3 up, 2 down
- Octahedral complexes
- Splitting occurs 2 up, 3 down
- When visible light shines on the transition metal, electrons can be promoted from a low energy to higher
- The colour we observe is the wavelength of light not absorbed
- White light - wavelength absorbed
- d-orbitals are degenerate, but when a ligand approaches, the orbitals are either destabilised or stabilised
- What is a complex?
- Transition metal surrounded by ligands
- Ligands
- Ionisation energy
- 1st ionisation energy
- The energy needed to remov 1 electron from a mole of gaseous atoms
- No anomalies as 1st electron is always removed from the 4 s orbital
- 2nd ionisation energy
- Cr -> Mn & Cu -> Zn
- Cr - electron removed from 3d orbital = more energy needed to promote
- Mn - electron removed from 4s shell = higher in energy, less energy needed to promote
- Cr -> Mn & Cu -> Zn
- 3rd ionisation energy
- Mn -> Fe
- Mn - Singly paired electrons = more stable
- Fe - inter repulsion between electrons = less energy to remove electron as destabilised
- Mn -> Fe
- 1st ionisation energy
- Catalysis
- Variable oxidation states make them good catalysts
- Types
- Heterogeneous
- Catalyst in different phase to reactants
- E.g solid catalyst with gaseous reactant particles - Fe in Haber process
- Catalyst in different phase to reactants
- Homogeneous
- Catalyst in same phase as reactants
- E.g
- Catalyst in same phase as reactants
- Heterogeneous
- Defintion
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