O Level Chemistry
Keywords to revise
1. States of Matter
Solid: A state of matter with a fixed shape and volume due to closely packed particles in a regular arrangement.
Liquid: A state of matter with a fixed volume but no fixed shape; particles are less tightly packed and can move past each other.
Gas: A state of matter with no fixed shape or volume; particles are widely spaced and move freely.
Kinetic Particle Theory: A theory that explains the properties of solids, liquids, and gases in terms of particle movement.
Diffusion: The movement of particles from an area of higher concentration to an area of lower concentration.
2. Atoms, Elements, and Compounds
Element: A pure substance consisting of only one type of atom.
Compound: A substance made of two or more elements chemically combined in a fixed ratio.
Mixture: A combination of two or more substances that are not chemically combined.
Atom: The smallest unit of an element that retains its chemical properties.
Proton number / Atomic number: The number of protons in the nucleus of an atom.
Mass number / Nucleon number: The total number of protons and neutrons in the nucleus of an atom.
Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons.
3. Chemical Bonding
Ionic bond: A strong electrostatic attraction between oppositely charged ions.
Covalent bond: A bond formed when a pair of electrons is shared between two atoms.
Metallic bonding: The electrostatic attraction between positive metal ions and a ‘sea’ of delocalized electrons.
Giant ionic structure: A lattice of alternating positive and negative ions held together by strong electrostatic forces.
Simple molecular structure: A structure consisting of molecules held together by weak intermolecular forces.
Giant covalent structure: A structure in which atoms are bonded by strong covalent bonds in a continuous network.
Alloy: A mixture of a metal with other elements that improves strength and hardness.
4. Stoichiometry
Relative atomic mass (Ar): The weighted average mass of an atom compared to 1/12th 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.
Empirical formula: The simplest whole-number ratio of atoms of different elements in a compound.
Molecular formula: The actual number of atoms of each element in a molecule.
Mole (mol): The unit of amount of substance, containing 6.02 × 10²³ particles (Avogadro’s constant).
Molar volume of gas: 24 dm³ at room temperature and pressure (r.t.p.).
5. Electrochemistry
Electrolysis: The decomposition of an ionic compound by passing an electric current.
Anode: The positive electrode in electrolysis.
Cathode: The negative electrode in electrolysis.
Electrolyte: A substance that conducts electricity and decomposes during electrolysis.
Oxidation: Loss of electrons.
Reduction: Gain of electrons.
Oxidising agent: A substance that oxidises another substance and is itself reduced.
Reducing agent: A substance that reduces another substance and is itself oxidised.
Electroplating: Coating an object with a thin layer of metal using electrolysis.
Fuel cell: A device that produces electricity from a chemical reaction between hydrogen and oxygen.
6. Chemical Energetics
Exothermic reaction: A reaction that releases thermal energy to the surroundings.
Endothermic reaction: A reaction that absorbs thermal energy from the surroundings.
Activation energy (Ea): The minimum energy required for a reaction to occur.
Bond energy: The energy required to break a bond.
7. Acids, Bases, and Salts
Acid: A substance that produces H⁺ ions in aqueous solution.
Base: A substance that neutralises an acid, producing a salt and water.
Alkali: A soluble base that produces OH⁻ ions in solution.
Neutralisation: The reaction between an acid and a base to produce salt and water.
Amphoteric oxides: Oxides that react with both acids and bases to form salts.
Salt: A compound formed when the hydrogen ion in an acid is replaced by a metal ion or ammonium ion.
Water of crystallisation: Water molecules that are chemically bonded within a crystal.
8. The Periodic Table
Periodic Table: A table of elements arranged in order of increasing atomic number.
Group: A vertical column in the Periodic Table where elements have similar chemical properties.
Period: A horizontal row in the Periodic Table.
Transition elements: Elements found in the middle block of the Periodic Table, known for variable oxidation states and coloured compounds.
Noble gases: Elements in Group VIII (18) that are unreactive due to a full outer electron shell.
9. Metals and Reactivity
Reactivity series: A ranking of metals based on their tendency to form positive ions.
Corrosion: The deterioration of metals due to reactions with oxygen and water.
Rusting: The oxidation of iron in the presence of oxygen and water, forming hydrated iron(III) oxide.
Galvanising: Coating iron or steel with zinc to prevent rusting.
Sacrificial protection: Protecting a metal by attaching a more reactive metal that corrodes instead.
10. Organic Chemistry
Homologous series: A series of organic compounds with the same functional group and general formula.
Functional group: A specific group of atoms that determines the chemical properties of an organic compound.
Saturated hydrocarbon: A hydrocarbon containing only single bonds.
Unsaturated hydrocarbon: A hydrocarbon containing at least one double or triple bond.
Polymer: A large molecule formed by the joining of many small monomer units.
Addition polymerisation: The process in which monomers with double bonds join to form a polymer without by-products.
Condensation polymerisation: The process in which monomers join with the elimination of a small molecule, like water.
Esterification: The reaction between a carboxylic acid and an alcohol to form an ester and water.
11. Chemistry of the Environment
Greenhouse effect: The trapping of heat in the Earth's atmosphere by greenhouse gases like CO₂ and CH₄.
Acid rain: Rainwater with a low pH caused by dissolved sulfur dioxide and nitrogen oxides.
Eutrophication: The process where excessive nutrients in water bodies cause oxygen depletion.
Fractional distillation: The separation of a mixture into fractions with different boiling points.
Catalytic converter: A device in car exhausts that reduces harmful emissions.
12. Experimental Techniques and Chemical Analysis
Chromatography: A technique used to separate and identify components in a mixture.
Rf value: The ratio of the distance traveled by a substance to the distance traveled by the solvent.
Titration: A technique used to determine the concentration of a solution.
Filtration: A method for separating insoluble solids from liquids.
Crystallisation: A method for obtaining pure solid crystals from a solution.
Flame test: A test for metal ions based on the colour they produce in a flame.