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

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

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

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 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

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

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

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

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

Optical isomerism

Octahedral complexes can display optical isomerism with bidentate ligands.

ligands differ in position in space relative to each other

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

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