Acid: A substance that produces hydrogen ions (H+) as the only positive ions when dissolved in water.
Activation energy: The minimum energy that molecules must possess during their collisions in order for a chemical reaction to occur.
Addition reaction: A reaction in which a molecule (element or compound) adds to an unsaturated compound to form a single new compound.
Alcohol: An organic compound containing the hydroxyl group, -OH.
Alkali: A base that is soluble in water.
Alkali metals: The elements in Group 1 of the Periodic Table.
Alkane: Hydrocarbon having the general formula CnH2n+2
Alkene: Hydrocarbon that contains one or more carbon-carbon double bonds. Alkenes with only one carbon-carbon double bond have the general formula CnH2n.
Alloy: A mixture of a metal with non-metals or other metals.
Anhydrous: Anhydrous salts are salts without water of crystallization.
Anion: A negatively charged ion which moves towards the anode during electrolysis.
Anode: A positively charged electrode in an electrolytic cell.
Aqueous: Describing the solution of a substance in water, i.e. the aqueous solution. In chemical equations, aqueous solutions are represented by the symbol (aq).
Atom: The smallest particle of an element.
Avogadro’s constant: The number of particles in one mole of a substance. Its value is 6 x 1023.
Avogadro’s law: At constant temperature, the volume of a gas is directly proportional to the number of moles of the gas present.
Base: A substance that reacts with an acid to form a salt and water only.
Boiling point: The temperature at which a liquid turns rapidly to its vapour.
Carboxylic acid: An organic acid containing the carboxyl group, -COOH.
Cathode: A negatively charged electrode in an electrolytic cell.
Cation: A positively charged ion which moves towards the cathode during electrolysis.
Chromatography: A method of separating the components in a mixture.
Collision theory: A chemical reaction can occur only if the reacting particles collide with one another.
Combustion: The chemical name for burning. Burning occurs when a substance reacts very rapidly with oxygen.
Compound: A substance formed in a chemical change when two or more elements are joined together.
Condensation: The process by which a vapour or a gas turns to liquid on cooling.
Corrosion: The wearing away of the surface of a metal by chemical reaction.
Covalent bond: The type of bond formed when electrons are shared between two non-metal atoms.
Cracking: The breaking down of long chain hydrocarbon molecules with heat and/or catalyst to produce smaller hydrocarbon molecules and/or hydrogen.
Decomposition: A chemical reaction that results in the breaking down of a compound into two or more components.
Diatomic molecule: A molecule that consists of two atoms.
Displacement reaction: A reaction in which an atom or molecule takes the place of another atom or molecule in a compound.
Distillation: A process of obtaining the pure solvent from a solution. When the solution is boiled, the solvent is vaporized and the vapour condenses to reform the pure liquid.
Electrode: A rod or a plate which carries electricity in or out of an electrolyte during electrolysis.
Electrolysis: A process in which electrical energy is used to cause a chemical reaction to occur, typically to separate the electrolyte into its elements.
Electron: A negatively charged sub-atomic particle that surrounds the nucleus of an atom.
Electronic configuration: The arrangement of electrons in the various shells of an atom or a molecule.
Element: A substance made from only one type of atom. It cannot be separated into simpler substances by chemical processes or by electricity.
Endothermic reaction: A reaction which absorbs heat from the surroundings.
Evaporation: The process by which a liquid changed to its vapour on the surface of the liquid.
Exothermic reaction: A process that gives off heat to the surroundings.
Fermentation: The conversion of glucose by microorganisms such as yeast into ethanol and carbon dioxide.
Filtrate: The clear liquid which passes through the filter during filtration.
Filtration: The process of separating a solid from a liquid or a solution.
Fossil fuels: Fuels produced many millions of years ago from the decaying remains of animals or plants, includes oil, natural gas and coal.
Fractional distillation: A process that separates the components in a mixture on the bases of their different boiling points. The component with the lowest boiling point boils off first and is distilled over.
Freezing point: The temperature at which a liquid changes to a solid.
Fuel: A substance that burns easily to produce energy.
Functional group: An atom or group of atoms that gives characteristic properties to an organic compound.
Giant structure: A three-dimensional network of atoms or ions packed together in a regular pattern.
Group: A vertical column of elements in the Periodic Table.
Halogen: The non-metallic elements in Group VII (7) of the Periodic Table.
Homologous series: A family of organic compounds with members of the family having the same functional group and similar chemical properties.
Hydrated salts: Salts that contain water of crystallization.
Hydrocarbons: Organic compounds made up from the elements hydrogen and carbon only.
Hydrogenation: The addition of a hydrogen molecule across a double bond.
Immiscible: Two liquids that do not mix.
Indicators: Compounds that have distinctly different colours in acidic and alkaline solutions.
Ion: A positively or negatively charged particle. It is formed when an atom or group of atoms loses or gains electrons.
Ionic bond: The electrostatic force that holds positive and negative ions together in an ionic compound.
Isotopes: Atoms of the same element that have the same atomic number but different mass/nucleon number.
Melting point: The temperature at which a solid changes to a liquid.
Metal: An element that is shiny and conducts electricity in the solid state. Metals burn in oxygen to form basic oxides or amphoteric oxides.
Mixture: A substance made by mixing other substances together. The components in a mixture can be easily separated by physical methods because they are not chemically joined together like in compounds.
Mole: The amount of a substance which contains 6 x 1023 particles.
Molecule: A group of atoms held together by covalent bonds. Molecules may be elements or compounds.
Nucleon number: Also known as the mass number. It is the sum of the number of protons and neutrons in the nucleus of an atom.
Neutralization: The reaction between an acid and a base to produce a salt and water only.
Neutron: A sub-atomic particle in the nucleus of an atom. It has a mass but no electrical charge.
Organic chemistry: The branch of chemistry that deals with carbon compounds.
Oxidation: A reaction where a substance gains oxygen or loses hydrogen. Oxidation is also defined as the loss of electron(s) or the increase in the oxidation state of the element.
Oxides: Compounds of an element with oxygen.
Oxidizing agent: A substance that brings about oxidation. It is itself reduced. An oxidizing agent is an acceptor of electrons.
Period: A horizontal row of elements in the Periodic Table.
Periodic table: A table that contains horizontal rows and vertical columns of elements. The elements are arranged in order of their atomic numbers and in accordance with their chemical properties.
pH scale: A scale that measures the acidity or alkalinity of a solution.
Pollution: The presence in the environment of toxic substances which are harmful to living things.
Polymer: A very large molecule built up of a number of repeating units called monomers.
Polymerization: A chemical reaction in which simple molecules, called monomers, react with each other to form larger molecules called polymers.
Polyunsaturated: Vegetable oils that contain many carbon-carbon double bonds in their molecules.
Precipitate: An insoluble solid that is produced in a solution as a result of a chemical reaction.
Protein: A polymer of amino acids.
Protons: Positively charged sub-atomic particles found in the nucleus of an atom.
Proton number: The number of protons in the nucleus of an atom.
Pure substance: A single substance which is not mixed with other substances. It has definite melting and boiling points. (e.g. pure water boils at exactly 100°C and freezes at 0°C)
Reactivity series: A list of elements in order of their reactivity. The more reactive the element, the higher its position in the series. An element higher up the series will displace a less reactive one from a solution of its salt.
Redox reaction: A reaction where both oxidation and reduction take place simultaneously.
Reducing agent: A substance that brings about reduction. It is itself oxidized. A reducing agent is a donor of electrons.
Reduction: The removal of oxygen, the addition of hydrogen, the gain of electrons, or the decrease in the oxidation state of the substance.
Relative atomic mass: The number of times the mass of one atom of an element is heavier than 1/12 of the mass of a carbon-12 atom.
Relative molecular mass: The sum of the relative atomic masses of each of the atoms in one molecule of a substance.
Residue: The solid which remains on the filter paper after filtration.
Respiration: The slow combustion of food in the cells of living organisms to release energy.
Rusting: The slow oxidation of iron in the presence of air and water to form hydrated iron (III) oxide (rust).
Salt: The ionic compound formed by the replacement of one or more hydrogen ions of an acid by a metallic ion or an ammonium ion.
Saturated hydrocarbons: Hydrocarbons that contain only single bonds between carbon atoms.
Solute: The substance that dissolves in a solvent to form a solution.
Solvent: The liquid in which a solute dissolves.
Steel: An alloy of iron and carbon.
Structural formula: A formula which shows how the atoms are arranged in a molecule.
Sublimation: The process of changing from the solid state directly to the gaseous state without passing through the liquid state.
Suspension: A mixture of a liquid and an insoluble solid where the insoluble solid remains suspended throughout the solution.
Titration: The gradual addition of a solution from a burette to another solution in a conical flask until the chemical reaction between the two solutions is complete; the 2 solutions tend to be an acid and an alkali.
Unsaturated molecule: Any hydrocarbon that contains one or more carbon-carbon double bonds.
Valence electrons: Electrons in the outer shell that are used by the atom for forming chemical bonds.
Water of crystallization: Water molecules that are chemically bonded in the crystals of some salts.