O-Level Chemistry Key Vocabulary

54 vocabulary flashcards covering fundamental definitions and concepts from O-Level Chemistry lecture notes.

Relative Atomic Mass (Ar)

The average mass of one atom of an element compared with 1⁄12 the mass of one atom of carbon-12.

Relative Molecular Mass (Mr)

The average mass of one molecule of a substance compared with 1⁄12 the mass of one atom of carbon-12.

Mole

The amount of substance that contains the same number of particles as there are atoms in 12 g of carbon-12.

Molar Mass

The mass of one mole of any substance.

Avogadro’s Law

Equal volumes of all gases, at the same temperature and pressure, contain the same number of particles.

Empirical Formula

The simplest whole-number ratio of the different atoms in a compound.

Molecular Formula

The exact number of each type of atom present in a molecule of a compound.

Structural Formula

A representation showing how the atoms are joined together in a molecule.

Limiting Reactant

The reactant that is completely used up first and thus limits the amount of products formed.

Element

A pure substance that cannot be broken down into simpler substances by chemical means.

Compound

A pure substance containing two or more different elements chemically combined together.

Mixture

A combination of two or more substances that are not chemically combined.

Molecule

A group of two or more atoms chemically bonded together.

Atom

The smallest particle of an element that retains its chemical properties.

Isotope

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

Proton Number

The number of protons in the nucleus of an atom (also called atomic number).

Nucleon Number

The total number of protons and neutrons in an atomic nucleus (mass number).

Ionic Bond

A strong electrostatic attraction between oppositely charged ions.

Covalent Bond

A bond formed by the sharing of at least one pair of valence electrons between atoms.

Giant Ionic Lattice

A large three-dimensional structure of alternating positive and negative ions held together by strong ionic bonds.

Simple Molecular Structure

Small molecules with strong covalent bonds within the molecule but weak intermolecular forces between molecules.

Acid

A substance that produces H⁺ ions when dissolved in water.

Base

Any metal oxide or hydroxide that reacts with an acid to produce a salt and water only.

Alkali

A soluble base that produces OH⁻ ions when dissolved in water.

Strong Acid

An acid that ionises completely in water to give a high concentration of H⁺ ions.

Weak Acid

An acid that partially ionises in water to give a low concentration of H⁺ ions.

Salt

An ionic compound containing a positive metal (or ammonium) ion and a negative non-metal ion.

Redox Reaction

A chemical reaction in which both oxidation and reduction occur simultaneously.

Oxidation

The gain of oxygen by a substance in a chemical reaction.

Reduction

The loss of oxygen by a substance in a chemical reaction.

Oxidising Agent

A substance that causes another to be oxidised and is itself reduced.

Reducing Agent

A substance that causes another to be reduced and is itself oxidised.

pH

A numerical scale that indicates the acidity or alkalinity of an aqueous solution.

Indicator

An organic compound that changes colour depending on the pH of a solution.

Acidic Oxide

An oxide that reacts with alkalis to form a salt and water only.

Basic Oxide

An oxide that reacts with acids to form a salt and water only.

Amphoteric Oxide

An oxide that reacts with both acids and alkalis to form a salt and water only.

Neutral Oxide

An oxide that does not react with either acids or alkalis.

Enthalpy Change

The overall heat energy change occurring in a reaction.

Exothermic Reaction

A reaction in which heat energy is released to the surroundings.

Endothermic Reaction

A reaction in which heat energy is absorbed from the surroundings.

Activation Energy

The minimum energy that reacting particles must have for a reaction to occur.

Catalyst

A substance that increases the rate of a reaction by lowering the activation energy and is chemically unchanged at the end.

Haber Process

An industrial process used for the manufacture of ammonia.

Electrolysis

The decomposition of a substance using an electric current.

Electrolyte

A molten or aqueous compound that conducts electricity by the movement of ions.

Electrode

A metal or carbon conductor through which current enters or leaves an electrolyte.

Inert Electrode

An electrode that does not react with the products of electrolysis.

Non-Electrolytes

Substances that do not conduct electricity in either molten or aqueous state.

Electroplating

The process of depositing a thin layer of metal on an object via electrolysis.

Simple Cell

A device that converts chemical energy into electrical energy.

Homologous Series

A family of compounds with the same functional group, general formula and similar chemical properties.

Functional Group

A specific group of atoms responsible for the characteristic reactions of a compound.

General Formula

A symbolic representation that applies to every member of a homologous series.

Hydrocarbon

A compound composed only of carbon and hydrogen atoms.

Saturated Hydrocarbon

A hydrocarbon containing only single bonds between carbon atoms.

Monomer

A small molecule that can be joined to identical molecules to form a polymer.

Polymer

A large molecule composed of repeating monomer units.

Addition Polymerisation

A reaction in which unsaturated monomers join to form a polymer without the loss of any atoms.

Condensation Polymerisation

A reaction in which monomers join to form a polymer with the elimination of small molecules such as water.