Keywords to revise

1. Atomic Structure

Isotope: Atoms of the same element with the same number of protons but different numbers of neutrons.

Atomic Radius: The distance from the nucleus to the outermost electron shell.

Ionic Radius: The radius of an ion, which varies depending on whether it is a cation or anion.

Principal Quantum Number (n): A number that indicates the energy level of an electron in an atom.

Ground State: The lowest energy state of an atom or molecule.

Free Radical: A species with one or more unpaired electrons.

Ionisation Energy (IE): is the minimum amount of energy required to remove an electron from an atom or ion in its gaseous state.

First Ionisation Energy: is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a +1 charge.

Sub-shell: A division of an electron shell, consisting of orbitals with the same energy level (e.g., s, p, d, f).

Orbital: A region in space where there is a high probability of finding an electron.

2. Atoms, Molecules, and Stoichiometry

Unified Atomic Mass Unit (u): One twelfth of the mass of a carbon-12 atom.

Relative Atomic Mass (Aᵣ): The average mass of an atom of an element relative to one twelfth of the mass of a carbon-12 atom.

Relative Molecular Mass (Mᵣ): The sum of the relative atomic masses of all atoms in a molecule.

Mole: The amount of substance containing the same number of particles as there are in 12 g of carbon-12.

Avogadro Constant: The number of particles in one mole of a substance (6.022 × 10²³ mol⁻¹).

Empirical Formula: The simplest whole number ratio of atoms of each element in a compound.

Molecular Formula: The actual number of atoms of each element in a molecule.

Anhydrous: A substance that contains no water.

Hydrated: A substance that contains water molecules within its structure.

Water of Crystallisation: Water molecules that are part of the crystalline structure of a compound.

Limiting Reagent: The reactant that is completely consumed in a reaction, limiting the amount of product formed.

Excess Reagent: The reactant that is not completely consumed in a reaction.

Stoichiometry: The calculation of reactants and products in chemical reactions based on balanced equations.

Percentage Yield: The ratio of the actual yield to the theoretical yield, expressed as a percentage.

3. Chemical Bonding

Electronegativity: The ability of an atom to attract electrons towards itself in a covalent bond.

Ionic Bonding: The electrostatic attraction between oppositely charged ions (cations and anions).

Metallic Bonding: The electrostatic attraction between positive metal ions and delocalised electrons.

Covalent Bonding: The electrostatic attraction between the nuclei of two atoms and a shared pair of electrons.

Coordinate (Dative Covalent) Bonding: A covalent bond where both electrons are provided by one atom.

Bond Energy: The energy required to break one mole of a particular covalent bond in the gaseous state.

Bond Length: The internuclear distance between two covalently bonded atoms.

Hydrogen Bonding: A strong intermolecular force between molecules containing N–H or O–H groups.

Van der Waals’ Forces: Weak intermolecular forces between molecules, including London dispersion forces and permanent dipole-dipole interactions.

σ Bond: A covalent bond formed by the head-on overlap of atomic orbitals.

π Bond: A covalent bond formed by the sideways overlap of p orbitals.

Hybridisation: The mixing of atomic orbitals to form new hybrid orbitals suitable for bonding.

Dipole-Dipole Forces: Intermolecular forces between polar molecules due to the attraction between positive and negative ends of dipoles.

London Dispersion Forces: Weak intermolecular forces caused by temporary dipoles in non-polar molecules.

Polarity: The distribution of electrical charge over atoms in a molecule, leading to a dipole moment.

4. States of Matter

Ideal Gas: A gas that has zero particle volume and no intermolecular forces of attraction.

Real Gas: A gas that deviates from ideal gas behavior due to particle volume and intermolecular forces.

Giant Ionic Lattice: A three-dimensional structure of oppositely charged ions held together by strong electrostatic forces.

Simple Molecular Structure: A structure where molecules are held together by weak intermolecular forces.

Giant Molecular Structure: A structure where atoms are covalently bonded in a continuous network.

Vapour Pressure: The pressure exerted by a vapour in equilibrium with its liquid or solid phase.

Boiling Point: The temperature at which the vapour pressure of a liquid equals the external pressure.

5. Chemical Energetics

Enthalpy Change (ΔH): The heat energy change at constant pressure.

Standard Conditions: 298 K and 101 kPa.

Activation Energy (Eₐ): The minimum energy required for a reaction to occur.

Hess’s Law: The total enthalpy change for a reaction is independent of the route taken.

Standard Enthalpy of Formation (ΔHf°): The enthalpy change when one mole of a compound is formed from its elements under standard conditions.

Standard Enthalpy of Combustion (ΔHc°): The enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions.

Exothermic Reaction: A reaction that releases heat energy to the surroundings (ΔH is negative).

Endothermic Reaction: A reaction that absorbs heat energy from the surroundings (ΔH is positive).

Calorimetry: The measurement of heat changes during chemical reactions.

6. Electrochemistry

Oxidation: The loss of electrons or an increase in oxidation number.

Reduction: The gain of electrons or a decrease in oxidation number.

Redox Reaction: A reaction involving both oxidation and reduction.

Oxidising Agent: A substance that accepts electrons and is reduced.

Reducing Agent: A substance that donates electrons and is oxidised.

Faraday Constant (F): The charge on one mole of electrons (96,500 C mol⁻¹).

Electrode Potential (E): The potential difference between an electrode and its solution.

Electrolyte: A substance that conducts electricity when dissolved in water or molten.

Electrolysis: The decomposition of an electrolyte by passing an electric current through it.

Faraday’s Laws of Electrolysis: Laws that relate the amount of substance produced at an electrode to the quantity of electricity passed.

7. Equilibria

Dynamic Equilibrium: A state where the rate of the forward reaction equals the rate of the reverse reaction, and concentrations remain constant.

Le Chatelier’s Principle: If a change is made to a system at equilibrium, the position of equilibrium shifts to minimize the change.

Equilibrium Constant (Kc): The ratio of the concentrations of products to reactants at equilibrium, each raised to the power of their stoichiometric coefficients.

Mole Fraction: The ratio of the number of moles of a component to the total number of moles in a mixture.

Partial Pressure: The pressure exerted by a single gas in a mixture of gases.

Bronsted-Lowry Acid: A substance that donates a proton (H⁺).

Bronsted-Lowry Base: A substance that accepts a proton (H⁺).

Conjugate Acid-Base Pair: Two species that differ by the presence or absence of a proton.

pH: A measure of the acidity or alkalinity of a solution, defined as pH = -log[H⁺].

pOH: A measure of the hydroxide ion concentration, defined as pOH = -log[OH⁻].

Kw (Ionic Product of Water): The equilibrium constant for the self-ionisation of water (Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 298 K).

8. Reaction Kinetics

Rate of Reaction: The change in concentration of a reactant or product per unit time.

Catalyst: A substance that increases the rate of a reaction without being consumed.

Homogeneous Catalyst: A catalyst in the same phase as the reactants.

Heterogeneous Catalyst: A catalyst in a different phase from the reactants.

Half-Life (t1/2): The time taken for the concentration of a reactant to decrease to half its initial value.

Intermediate: A species formed in one step of a reaction mechanism and consumed in a subsequent step.

Rate Constant (k): A proportionality constant in the rate equation that relates the rate of reaction to the concentration of reactants.

Order of Reaction: The power to which the concentration of a reactant is raised in the rate equation.

Rate-Determining Step: The slowest step in a reaction mechanism, which determines the overall rate of the reaction.

9. The Periodic Table

Periodicity: The repeating trends in physical and chemical properties of elements across periods and groups.

Oxidation Number: A measure of the degree of oxidation of an atom in a substance.

Electron Shielding: The reduction in the effective nuclear charge on an electron due to the presence of inner-shell electrons.

Effective Nuclear Charge: The net positive charge experienced by an electron in an atom, taking into account shielding.

10. Group 2

Thermal Decomposition: The breakdown of a compound into simpler substances when heated.

Thermal Stability: The resistance of a compound to decomposition when heated.

Alkaline Earth Metals: The elements in Group 2 of the Periodic Table (e.g., magnesium, calcium).

Thermal Stability of Carbonates: The resistance of carbonates to decomposition when heated.

11. Group 17

Halogen: A group 17 element (e.g., fluorine, chlorine, bromine, iodine).

Hydrogen Halide: A compound formed between hydrogen and a halogen (e.g., HCl, HBr).

Disproportionation: A reaction where a single substance is both oxidised and reduced.

Halogen Displacement Reactions: Reactions where a more reactive halogen displaces a less reactive halogen from its compound.

Halide Ions: Negatively charged ions of halogens (e.g., Cl⁻, Br⁻, I⁻).

12. Nitrogen and Sulfur

Ammonium Ion (NH₄⁺): A positively charged ion formed by the protonation of ammonia.

Acid Rain: Rainwater with a pH below 5.6, caused by the dissolution of acidic gases like SO₂ and NO₂.

Photochemical Smog: A type of air pollution formed by the reaction of sunlight with nitrogen oxides and hydrocarbons.

Ammonia (NH₃): A compound of nitrogen and hydrogen, which acts as a weak base.

Sulfur Dioxide (SO₂): A gas formed by the combustion of sulfur-containing fuels, contributing to acid rain.

13. Organic Chemistry

Hydrocarbon: A compound containing only carbon and hydrogen atoms.

Functional Group: A group of atoms responsible for the characteristic reactions of a compound.

Homologous Series: A series of compounds with the same functional group and similar chemical properties.

Structural Isomerism: Compounds with the same molecular formula but different structural arrangements.

Stereoisomerism: Compounds with the same structural formula but different spatial arrangements.

Chiral Centre: A carbon atom bonded to four different groups, leading to optical isomerism.

Geometrical Isomerism: A form of stereoisomerism where compounds have the same structure but different spatial arrangements due to restricted rotation around a double bond.

Optical Isomerism: A form of stereoisomerism where compounds are non-superimposable mirror images of each other.

Homolytic Fission: The breaking of a covalent bond where each atom retains one electron, forming free radicals.

Heterolytic Fission: The breaking of a covalent bond where one atom retains both electrons, forming ions.

Nucleophile: A species that donates a pair of electrons to form a covalent bond.

Electrophile: A species that accepts a pair of electrons to form a covalent bond.

14. Hydrocarbons

Alkane: A saturated hydrocarbon with single bonds only.

Alkene: An unsaturated hydrocarbon containing at least one carbon-carbon double bond.

Free Radical: A species with one or more unpaired electrons.

Cracking: The breakdown of long-chain hydrocarbons into shorter-chain hydrocarbons.

Alkyne: An unsaturated hydrocarbon containing at least one carbon-carbon triple bond.

Polymer: A large molecule formed by the repetition of small monomer units.

15. Halogen Compounds

Halogenoalkane: An alkane with one or more hydrogen atoms replaced by halogen atoms.

Nucleophilic Substitution: A reaction where a nucleophile replaces a leaving group in a molecule.

SN1 Mechanism: A nucleophilic substitution reaction where the rate-determining step involves the formation of a carbocation.

SN2 Mechanism: A nucleophilic substitution reaction where the rate-determining step involves a simultaneous bond-breaking and bond-forming process.

Elimination Reaction: A reaction where a small molecule (e.g., HX) is removed from a larger molecule, forming a double bond.

16. Hydroxy Compounds

Alcohol: A compound containing a hydroxyl (–OH) group bonded to a carbon atom.

Primary Alcohol: An alcohol where the hydroxyl group is attached to a carbon atom bonded to only one other carbon atom.

Secondary Alcohol: An alcohol where the hydroxyl group is attached to a carbon atom bonded to two other carbon atoms.

Tertiary Alcohol: An alcohol where the hydroxyl group is attached to a carbon atom bonded to three other carbon atoms.

Esterification: The reaction between an alcohol and a carboxylic acid to form an ester.

Dehydration: The removal of water from a molecule, often leading to the formation of a double bond.

Oxidation of Alcohols: The conversion of alcohols to aldehydes, ketones, or carboxylic acids.

17. Carbonyl Compounds

Aldehyde: A compound containing a carbonyl group (C=O) bonded to at least one hydrogen atom.

Ketone: A compound containing a carbonyl group (C=O) bonded to two carbon atoms.

Nucleophilic Addition: A reaction where a nucleophile adds to a carbonyl group.

Fehling’s Solution: A reagent used to test for the presence of aldehydes, which reduces to give a red precipitate of copper(I) oxide.

Tollens’ Reagent: A reagent used to test for aldehydes, which forms a silver mirror when reduced.

18. Carboxylic Acids and Derivatives

Carboxylic Acid: A compound containing a carboxyl group (–COOH).

Ester: A compound formed by the reaction of an alcohol with a carboxylic acid.

Acyl Group: A functional group with the structure R–CO–.

Ester Hydrolysis: The breakdown of an ester into a carboxylic acid and an alcohol in the presence of water.

Acyl Chloride Hydrolysis: The reaction of an acyl chloride with water to form a carboxylic acid and HCl.

19. Nitrogen Compounds

Amine: A compound derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups.

Nitrile: A compound containing a –C≡N group.

Zwitterion: A molecule with both positive and negative charges, but overall neutral.

Amide Hydrolysis: The breakdown of an amide into a carboxylic acid and an amine in the presence of water or acid.

Nitrile Hydrolysis: The breakdown of a nitrile into a carboxylic acid and ammonia in the presence of water or acid.

20. Polymerisation

Addition Polymerisation: A reaction where monomers add together to form a polymer without the loss of any atoms.

Condensation Polymerisation: A reaction where monomers join together with the loss of small molecules like water.

Biodegradable Polymer: A polymer that can be broken down by natural processes.

Addition Polymer: A polymer formed by the addition of monomer units without the loss of any atoms (e.g., polyethene).

Condensation Polymer: A polymer formed by the reaction of monomers with the loss of small molecules like water (e.g., nylon).

21. Organic Synthesis

Synthetic Route: A sequence of reactions used to convert starting materials into a desired product.

By-Product: A secondary product formed in a chemical reaction.

Retrosynthesis: The process of working backwards from a target molecule to identify suitable starting materials and synthetic routes.

Functional Group Interconversion: The transformation of one functional group into another during a synthetic route.

22. Analytical Techniques

Infrared Spectroscopy: A technique used to identify functional groups in a molecule based on the absorption of infrared radiation.

Mass Spectrometry: A technique used to determine the molecular mass and structure of a compound based on the mass-to-charge ratio of ions.

Retention Time: The time taken for a compound to pass through a chromatography column.

Rf Value: The ratio of the distance travelled by a compound to the distance travelled by the solvent in chromatography.

Chemical Shift: The position of a peak in an NMR spectrum, measured in parts per million (ppm).

Chromatography: A technique used to separate and identify components of a mixture based on their movement through a stationary phase.

Mass Spectrum: A plot of the relative abundance of ions versus their mass-to-charge ratio (m/z).

23. Chemical Energetics (A Level)

Lattice Energy: The energy change when one mole of an ionic solid is formed from its gaseous ions.

Enthalpy of Hydration: The energy change when one mole of gaseous ions is dissolved in water.

Entropy (S): A measure of the disorder or randomness of a system.

Gibbs Free Energy (ΔG): A measure of the spontaneity of a reaction, given by ΔG = ΔH – TΔS.

Born-Haber Cycle: A cycle used to calculate lattice energy from other thermodynamic data.

Enthalpy of Atomisation (ΔHₐₜ): The enthalpy change when one mole of gaseous atoms is formed from an element in its standard state.

First Electron Affinity (EA): The energy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous ions.

24. Electrochemistry (A Level)

Standard Electrode Potential (E°): The potential difference between an electrode and a standard hydrogen electrode under standard conditions.

Nernst Equation: An equation that relates the electrode potential to the concentration of ions in solution.

Standard Hydrogen Electrode (SHE): An electrode used as a reference in measuring standard electrode potentials.

Standard Cell Potential (E°cell): The potential difference between two half-cells under standard conditions.

25. Equilibria (A Level)

Buffer Solution: A solution that resists changes in pH when small amounts of acid or base are added.

Solubility Product (Kₛₚ): The equilibrium constant for the dissolution of a sparingly soluble salt.

Common Ion Effect: The suppression of the solubility of a salt by the presence of a common ion.

Buffer Capacity: The ability of a buffer solution to resist changes in pH when small amounts of acid or base are added.

26. Reaction Kinetics (A Level)

Rate Equation: An equation that relates the rate of a reaction to the concentration of reactants.

Rate-Determining Step: The slowest step in a reaction mechanism, which determines the overall rate of the reaction.

Intermediate: A species formed in one step of a reaction mechanism and consumed in a subsequent step.

27. Group 2 (A Level)

Enthalpy of Solution (ΔHsol): The enthalpy change when one mole of a substance dissolves in water.

28. Transition Elements (A Level)

Transition Element: A d-block element that forms one or more stable ions with incomplete d orbitals.

Ligand: A molecule or ion that donates a pair of electrons to a metal ion to form a coordinate bond.

Complex Ion: A metal ion surrounded by ligands.

Stability Constant (Kstab): The equilibrium constant for the formation of a complex ion.

Ligand Exchange: The replacement of one ligand by another in a complex ion.

Degenerate Orbitals: Orbitals that have the same energy level.

Ligand Field Theory: A theory that explains the bonding and properties of transition metal complexes.

Crystal Field Splitting (ΔE): The energy difference between the split d orbitals in a transition metal complex.

29. Organic Chemistry (A Level)

Aromatic Compound: A compound containing a benzene ring or similar structure with delocalised π electrons.

Electrophilic Substitution: A reaction where an electrophile replaces a hydrogen atom in an aromatic compound.

Electrophilic Aromatic Substitution: A reaction where an electrophile replaces a hydrogen atom in an aromatic ring (e.g., nitration of benzene).

30. Hydrocarbons (A Level)

Arene: An aromatic hydrocarbon containing one or more benzene rings.

Friedel-Crafts Reaction: A reaction where an alkyl or acyl group is introduced to an aromatic ring.

31. Halogen Compounds (A Level)

Halogenoarene: An aromatic compound with one or more halogen atoms attached to the benzene ring.

Aryl Halide: A halogen atom bonded to an aromatic ring.

32. Hydroxy Compounds (A Level)

Phenol: An aromatic compound with a hydroxyl group attached to a benzene ring.

Phenoxide Ion: The anion formed when phenol loses a proton.

33. Carboxylic Acids and Derivatives (A Level)

Acyl Chloride: A compound containing a –COCl group.

34. Nitrogen Compounds (A Level)

Phenylamine: An aromatic amine with the formula C₆H₅NH₂.

Azo Compound: A compound containing the –N=N– group, often used as dyes.

Diazonium Salt: A compound containing the –N₂⁺ group.

35. Polymerisation (A Level)

Polyamide: A polymer formed by the reaction of a diamine with a dicarboxylic acid.

36. Organic Synthesis (A Level)

Multi-step Synthesis: A sequence of reactions used to convert simple starting materials into complex products.

37. Analytical Techniques (A Level)

Tetramethylsilane (TMS): A standard reference compound used in NMR spectroscopy.

NMR Spectroscopy: A technique used to determine the structure of organic molecules by analysing the magnetic properties of atomic nuclei.

Chemical Shift: The position of a peak in an NMR spectrum, measured in parts per million (ppm).

Online videos

1: Atomic Structure: 

2: Atoms, Molecules and Stoichiometry: 

3: Electrons in Atoms: 

4: Chemical Bonding: 

5. States of matter

6. Energy changes

7. Redox reactions

8. Equilibria

9. Rates of reaction

10. Periodicity

11. Group 2

12. Group 17

13. Nitrogen and sulfur

14. Introduction to organic chemistry

15. Hydrocarbons

16. Halogenoalkanes

17. Alcohols, esters and carboxylic acids

18. Carbonyl compounds

19. Lattice energy

20. Electrochemistry

21. Further aspects of equilibria

22. Reaction kinetics

23. Entropy and Gibbs free energy

24. Transition elements

25. Benzene and its compounds

26. Carboxylic acids and their derivatives

27. Organic nitrogen compounds

28. Polymerisation

29. Analytical chemistry