Transition Metals
11 November 2024 11:07
Transition metal: d-block element that forms one or more stable ions with incompletely-filled
d-orbitals
Electronic configurations:
• 4s electrons have less energy than 3d electrons so the 4s orbitals will be filled before the 3d
orbitals
• 4s electrons will be removed before the 3d electrons when forming ions
• Having 5 or 10 electrons in the d subshell is more stable so the electron configurations are
different for Cr and Cu
Oxidation numbers:
• The 4s and 3d sub-shells only slightly differ in energy so similar amounts of energy can be used
to remove different numbers of electrons, resulting in variable oxidation states (numbers)
• +2 is a common oxidation state due to the removal of the 4s electrons
Complex Ions:
• Transition metals form complexes where there is a central ion surrounded by ligands
• Ligand: molecule or ion that forms a coordinate bond with a transition metal by donating a pair of
electrons to it (into its d-orbital)
• Coordination number: the number of coordinate bonds that are formed with the transition metal
ion
• To show a complex, use square brackets (ion), arrows for coordinate bonds and shape of the
molecule is maintained:
Naming complex ions:
• Number of ligands/ligand name/element/charge (o.n.)
Octahedral If the ligand has no charge (H2O), the charge will just be
• The overall charge of the complex is the sum of the charges from the
central ion and the ligands. the oxidation number of the central metal ion
• For anions, the metal ends in ate (ferrate, cuprate…)
• Types of ligand:
- Monodentate: Have one lone pair of electrons to form 1 dative bond with the metal ion:
Tetrachlorocuprate (II)
- Bidentate: Have two lone pairs of electrons to form 2 dative bonds with the metal ion
en
Tris(ethylenediamine)cobalt(III)
- Multidentate: Have more than two lone pairs of electrons to form more than 2 dative bonds with
the metal ion
EDTA4- EDTA is hexadentate
(Ethylenediaminetetraacetato)copper(II)
Cis-platin:
• Example of a complex with four coordinate bonds that doesen't have a tetrahedral shape
Square planar shape (90º)
Uses:
• Chemotherapy drug to treat cancer
• Passes through the cell membrane and undergoes ligand exchange where the chlorines are
replaced by water molecules
• Inhibits DNA replication
• Only the cis isomer is effective (trans is toxic)
Haemoglobin:
• Iron (II) complex with four multidentate ligands (haem groups)
• Oxygen atoms form a dative covalent bond with the iron(II)
• CO is a better ligand than oxygen and binds strongly to the iron(II) in a ligand exchange reaction
• This prevents oxygen from being carried to the cells
Coloured Ions:
• The d-orbitals in transition metals differ slightly in energy when ligands are attached:
• When external energy is supplied (light), electrons can be promoted to a higher energy level by
absorbing part of the energy
• The amount of energy absorbed depends on the energy difference between the energy levels
• The remaining energy that hasn't been absorbed is transmitted as light in the electromagnetic
spectrum
• Ex: If an electron absorbs a wavelength of light corresponding to a red colour, the colour seen
will be green
Factors that affect changes in colour:
Ligands:
• The greater the charge density of the ligand, the stronger the attraction with the metal ion Colourless ions:
• Therefore the greater the energy difference between the split d-orbitals so more energy required Sc3+: No d electrons left to transfer so no energy absorbed
to promote electrons Zn2+ and Cu+: d shell is full so no space for electron transfer
• This changes the wavelengths the electron absorbs so the colour absorbed is different hence therefore no energy absorbed
the complementary colour observed changes
11 November 2024 11:07
Transition metal: d-block element that forms one or more stable ions with incompletely-filled
d-orbitals
Electronic configurations:
• 4s electrons have less energy than 3d electrons so the 4s orbitals will be filled before the 3d
orbitals
• 4s electrons will be removed before the 3d electrons when forming ions
• Having 5 or 10 electrons in the d subshell is more stable so the electron configurations are
different for Cr and Cu
Oxidation numbers:
• The 4s and 3d sub-shells only slightly differ in energy so similar amounts of energy can be used
to remove different numbers of electrons, resulting in variable oxidation states (numbers)
• +2 is a common oxidation state due to the removal of the 4s electrons
Complex Ions:
• Transition metals form complexes where there is a central ion surrounded by ligands
• Ligand: molecule or ion that forms a coordinate bond with a transition metal by donating a pair of
electrons to it (into its d-orbital)
• Coordination number: the number of coordinate bonds that are formed with the transition metal
ion
• To show a complex, use square brackets (ion), arrows for coordinate bonds and shape of the
molecule is maintained:
Naming complex ions:
• Number of ligands/ligand name/element/charge (o.n.)
Octahedral If the ligand has no charge (H2O), the charge will just be
• The overall charge of the complex is the sum of the charges from the
central ion and the ligands. the oxidation number of the central metal ion
• For anions, the metal ends in ate (ferrate, cuprate…)
• Types of ligand:
- Monodentate: Have one lone pair of electrons to form 1 dative bond with the metal ion:
Tetrachlorocuprate (II)
- Bidentate: Have two lone pairs of electrons to form 2 dative bonds with the metal ion
en
Tris(ethylenediamine)cobalt(III)
- Multidentate: Have more than two lone pairs of electrons to form more than 2 dative bonds with
the metal ion
EDTA4- EDTA is hexadentate
(Ethylenediaminetetraacetato)copper(II)
Cis-platin:
• Example of a complex with four coordinate bonds that doesen't have a tetrahedral shape
Square planar shape (90º)
Uses:
• Chemotherapy drug to treat cancer
• Passes through the cell membrane and undergoes ligand exchange where the chlorines are
replaced by water molecules
• Inhibits DNA replication
• Only the cis isomer is effective (trans is toxic)
Haemoglobin:
• Iron (II) complex with four multidentate ligands (haem groups)
• Oxygen atoms form a dative covalent bond with the iron(II)
• CO is a better ligand than oxygen and binds strongly to the iron(II) in a ligand exchange reaction
• This prevents oxygen from being carried to the cells
Coloured Ions:
• The d-orbitals in transition metals differ slightly in energy when ligands are attached:
• When external energy is supplied (light), electrons can be promoted to a higher energy level by
absorbing part of the energy
• The amount of energy absorbed depends on the energy difference between the energy levels
• The remaining energy that hasn't been absorbed is transmitted as light in the electromagnetic
spectrum
• Ex: If an electron absorbs a wavelength of light corresponding to a red colour, the colour seen
will be green
Factors that affect changes in colour:
Ligands:
• The greater the charge density of the ligand, the stronger the attraction with the metal ion Colourless ions:
• Therefore the greater the energy difference between the split d-orbitals so more energy required Sc3+: No d electrons left to transfer so no energy absorbed
to promote electrons Zn2+ and Cu+: d shell is full so no space for electron transfer
• This changes the wavelengths the electron absorbs so the colour absorbed is different hence therefore no energy absorbed
the complementary colour observed changes
