TOPIC 01 • REDOX EQUILIBRIA
Redox Equilibria
Redox reactions involve the transfer of electrons between chemical species. Oxidation and reduction occur simultaneously.
Oxidation and Reduction
- Oxidation involves loss of electrons.
- Reduction involves gain of electrons.
- An oxidising agent accepts electrons.
- A reducing agent donates electrons.
Oxidation Is Loss, Reduction Is Gain.
Standard Electrode Potentials
Standard electrode potentials allow the relative tendency of chemical species to be reduced to be compared.
Oxidation
Electrons released
Reduction
Electrons accepted
A positive E°cell indicates thermodynamic feasibility under standard conditions.
TOPIC 02 • TRANSITION METALS
Transition Metals
Transition metals are important because of their variable oxidation states, complex ions, coloured compounds and catalytic properties.
Definition
A transition element is an element whose atom has a partially filled d subshell, or which forms at least one ion with a partially filled d subshell.
Variable Oxidation States
Transition metals can form ions with different oxidation states because the 3d and 4s electrons have similar energies.
Complex Ions
A complex ion contains a central metal ion surrounded by ligands which donate lone pairs of electrons to the metal.
Ligands
- Monodentate ligands form one coordinate bond.
- Bidentate ligands form two coordinate bonds.
- Multidentate ligands can form several coordinate bonds.
TOPIC 03 • COLOUR & LIGAND EXCHANGE
Colours and Ligand Exchange
Many transition-metal complexes are coloured because electrons can absorb visible radiation and undergo transitions between split d-orbitals.
Why Are Complexes Coloured?
The colour observed is complementary to the wavelengths of visible light absorbed by the complex.
Ligand Substitution
Ligand exchange occurs when one ligand is replaced by another ligand in a complex ion. This can change the coordination environment and colour.
Precipitation Reactions
Transition-metal ions can form insoluble hydroxides and other compounds when suitable reagents are added.
TOPIC 04 • TRANSITION-METAL REDOX
Transition Metal Redox Chemistry
Transition metals commonly participate in redox reactions because they can exist in several oxidation states.
Vanadium
Vanadium provides an important example of a metal displaying several oxidation states and differently coloured aqueous ions.
Chromium
Chromium compounds demonstrate changes in oxidation state and colour during redox reactions.
Manganese
Manganese compounds, including permanganate ions, are important oxidising agents.
Be able to use half-equations and oxidation numbers to analyse redox reactions.
TOPIC 05 • ORGANIC CHEMISTRY
Arenes
Arenes are aromatic hydrocarbons containing one or more benzene rings.
Benzene
Benzene has a planar hexagonal structure with delocalised electrons spread across the ring.
The delocalised π-electron system gives benzene unusual stability.
Electrophilic Substitution
Benzene commonly undergoes electrophilic substitution reactions rather than addition reactions.
Nitration
Benzene reacts with concentrated nitric acid in the presence of concentrated sulfuric acid to form nitrobenzene.
Friedel–Crafts Reactions
Friedel–Crafts reactions introduce alkyl or acyl groups into an aromatic ring.
TOPIC 06 • PHENOLS
Phenols
Phenols contain a hydroxyl group directly attached to an aromatic ring.
Acidity
Phenol is more acidic than an alcohol because the phenoxide ion formed after loss of H⁺ is stabilised by delocalisation.
Important Reactions
- Reaction with sodium.
- Reaction with sodium hydroxide.
- Reaction with bromine water.
- Nitration.
Compare phenol with alcohols by considering the stability of the conjugate base.
TOPIC 07 • ORGANIC NITROGEN
Amines
Amines are organic compounds containing nitrogen. They can be classified as primary, secondary or tertiary.
Basicity
Amines act as bases because the nitrogen atom contains a lone pair of electrons that can accept a proton.
Preparation of Amines
- Reaction of haloalkanes with ammonia.
- Reduction of nitriles.
- Reduction of nitro compounds.
TOPIC 08 • AMIDES
Amides
Amides contain the functional group derived from a carboxylic acid in which the hydroxyl group has been replaced by nitrogen.
Formation
Acyl chlorides can react with ammonia or amines to form amides.
Hydrolysis
Amides can undergo hydrolysis under acidic or alkaline conditions.
Recognise the combination of a carbonyl group and nitrogen when identifying an amide.
TOPIC 09 • AMINO ACIDS
Amino Acids
Amino acids contain both an amino group and a carboxylic acid group.
Zwitterions
In aqueous solution, amino acids can exist as zwitterions containing both a positive and a negative charge.
Amino acids can act as both acids and bases because they contain acidic and basic functional groups.
Peptide Bonds
Amino acids join together through condensation reactions to form peptide bonds.
TOPIC 10 • PROTEINS
Proteins
Proteins are polymers made from amino acids joined by peptide bonds.
Primary Structure
The primary structure is the sequence of amino acids in a polypeptide chain.
Secondary Structure
Secondary structure includes structures such as α-helices and β-sheets.
Tertiary Structure
Tertiary structure describes the overall three-dimensional folding of a polypeptide chain.
Hydrogen Bonding
Hydrogen bonds and other intermolecular interactions help maintain protein structure.
Primary → Secondary → Tertiary
TOPIC 11 • ORGANIC SYNTHESIS
Organic Synthesis
Organic synthesis involves converting one organic compound into another through a sequence of chemical reactions.
Planning a Synthesis
- Identify the starting material.
- Identify the target molecule.
- Choose suitable reagents.
- Choose appropriate reaction conditions.
- Consider purification and yield.
Unit 5 can include synoptic questions requiring knowledge from earlier units.
TOPIC 12 • ORGANIC ANALYSIS
Organic Analysis
Infrared Spectroscopy
Infrared spectroscopy can be used to identify functional groups from characteristic absorption frequencies.
Mass Spectrometry
Mass spectrometry can provide information about molecular mass and fragmentation patterns.
NMR Spectroscopy
Nuclear magnetic resonance spectroscopy provides information about different chemical environments within a molecule.
Combine several pieces of analytical evidence rather than relying on one spectrum alone.
EXAM PRACTICE
Chemistry 5 Mixed Practice
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An element whose atom has a partially filled d subshell, or which forms at least one ion with a partially filled d subshell.
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Electrons can absorb visible radiation and undergo transitions between split d-orbitals. The remaining transmitted or reflected light gives the complex its observed colour.
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Electrophilic substitution.
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The nitrogen atom has a lone pair of electrons that can accept a proton.
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A bond formed between the carboxyl group of one amino acid and the amino group of another amino acid during a condensation reaction.
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To convert an available starting compound into a desired organic product through a suitable sequence of reactions.
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A species that donates a lone pair of electrons to a central metal ion to form a coordinate bond.
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The phenoxide ion formed when phenol loses H⁺ is stabilised by delocalisation of the negative charge into the aromatic ring.
QUICK REVIEW
Unit 5 Formula & Concept Vault
Link structure to properties, oxidation state to redox behaviour, ligands to complex geometry and functional groups to organic reactions. In unfamiliar questions, use the chemical evidence given rather than relying only on memorised examples.