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3.2.5-6 Inorganic Chemistry Y2 (1) (Properties: (incomplete d sub-level in…
3.2.5-6 Inorganic Chemistry Y2 (1)
Properties:
incomplete d sub-level in atoms or ions, 4s shell is filled first
variable oxidation state; have more than one oxidation state in their compounds; can take part in many redox reaction
catalytic activity; speed up rate of reaction without being used up or chemically changed
ligand: a molecule of ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons
complex: central metal atom or ion surrounded by ligands
Co-ordination number: number of co-ordinate bonds to the central metal atom or ion
Cu has a full 3d shell, Cr has a half full 3d shell and one 4s electron
Transition metal: a metal that forms at least one stable ion with a part full d-shell of electrons; Sc and Zn are not transition metals
Substitution reactions to form complex ions
monodentate ligands: molecule/ion has one atom with a lone pair of electrons that can bind to a transition metal ion
e.g. H₂O, NH₃, Cl ⁻
bidentate ligands: molecule/ion has two atoms a lone pairs of electrons that can bind to a transition metal ion
e.g. H₂NCH₂CH₂NH₂ (en), C₂O₄²(oxalate)⁻
multidentate ligands: more than one atom with a lone pair of electrons that can bind to a transition metal ion
e.g. EDTA⁴⁻; acts as a hexadentate ligand using lone pairs on four oxygens and both nitrogen atoms; forms chelates
exchange of NH₃ and H₂O ligands occurs without change of coordination number e.g. Co²⁺ and Cu²⁺
substitution may be incomplete e.g. formation of [Cu(NH₃)₄(H₂O)₂]²⁺
exchange of the ligand H₂O by Cl⁻ can involve a change in coordination number e.g. Co²⁺, Cu²⁺, Fe³⁺
Haemoglobin
Haem is an iron(II) complex with a multidentate ligand
oxygen forms a co-ordinate bond to Fe(II) in haemoglobin, enabling oxygen to be transported in the blood
carbon monoxide is toxic because it replaces oxygen co-ordinately bonded to Fe(II) in haemoglobin; carbon monoxide is a better ligand than oxygen
chelate effect:
bidentate and multidentate ligands replace monodentate ligands from complexes; chelate complexes with polydentate ligands are favoured over complexes with monodentate ligands
increase in number of particles causes a significant increase in entropy with drives reaction to the right
chelate: complex ions with polydentate ligands; can be used to effectively remove d-block metal ions from solution
e.g. [Cu(H₂O)₆]²⁺(aq) + EDTA⁴⁻(aq) → [CuEDTA]²⁻(aq) + 6H₂O(l)
two species are replaced by seven
Shapes of complex ions:
Octahedral complexes can display cis–trans isomerism (a special case of E–Z isomerism) with monodentate ligands and optical isomerism with bidentate ligands.
Ag⁺ forms the linear complex [Ag(NH₃)₂]⁺ as used in Tollens’ reagent; aldehydes reduce [Ag(NH₃)₂]⁺ to Ag
co-ordination number:
the number of co-ordinate bonds a transition metal can make to ligands
co-ordination number 6; formed with smaller ligands e.g. H₂O, NH₃
usually octahedral shape; [Co(NH₃)₆]³⁺
co-ordination number 4; formed with larger ligands e.g. Cl⁻
usually tetrahedral shape; [CoCl₄]²⁻
co-ordination number 4: some ions
square planar shape; [NiCN₄]²⁻
Cl⁻ ligand is larger than the uncharged ligands NH₃ and H₂O
NH₃ and H₂O are similar in size and are uncharged
complex ions can have a positive charge or a negative charge
geometrical isomerism:
Octahedral complexes can display cis–trans isomerism (a special case of E–Z isomerism) with monodentate ligands
Square planar complexes can display cis–trans isomerism; Cisplatin is the cis isomer.
cis=same, trans=opposite
ligands differ in position in space relative to each other
Optical isomerism
Octahedral complexes can display optical isomerism with bidentate ligands.
isomers are non-superimposable mirror images of each other
can be distinguished by shining plane polarised light, as isomers will rotate light in opposite directions
Formation of coloured ions:
Colour arises when some of the wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected.
transition metals are coloured as they part filled d-shells; d electrons move from the ground state to a (higher) excited state when light is absorbed.
∆E = hν = hc/λ
The energy difference between the ground state and the excited state of the d electrons
Changes in oxidation state, co-ordination number and ligand alter ∆E and this leads to a change in colour.
∆E = energy change; J
h = Planck's constant
v= frequency, s⁻¹
c= velocity of light, ms⁻¹
λ = wavelength, m
frequency is related to energy and colour of light
e.g. violet is of high energy and high frequency
The absorption of visible light is used in spectroscopy.
A simple colorimeter can be used to determine the concentration of coloured ions in solution; uses a light source and detector to measure the amount of light of a particular wavelength that passes through a coloured solution; more concentrated solution = less light transmitted through solution; plot a calibration curve
Sammer Sheikh