IGCSE Chemistry Comprehensive Vocabulary

Essential vocabulary flashcards covering atomic structure, chemical bonding, stoichiometry, states of matter, acids and bases, redox, equilibrium, and organic chemistry based on Cambridge IGCSE Chemistry lecture notes.

Proton number

The number of protons in the nucleus of an atom, also known as the atomic number, which uniquely identifies an element.

Nucleon number

The total number of protons and neutrons in the nucleus of an atom, also called the mass number.

Isotopes

Atoms of the same element that have the same proton number but different nucleon numbers, resulting in different numbers of neutrons.

Valence electrons

The electrons situated in the outermost electron shell of an atom that determine how the element reacts and forms bonds.

Element

A pure substance consisting of only one type of atom that cannot be broken down into simpler substances by chemical means.

Compound

A substance formed from two or more different elements chemically bonded together in fixed proportions.

Mixture

A combination of two or more substances that are not chemically bonded, can be present in any proportion, and can be separated by physical methods.

Cation

A positively charged ion formed when an atom loses one or more electrons.

Anion

A negatively charged ion formed when an atom gains one or more electrons.

Ionic bond

The strong electrostatic attraction between oppositely charged ions, typically formed between a metal and a non-metal.

Covalent bond

A chemical bond formed when two non-metal atoms share a pair of electrons to achieve a stable outer-shell configuration.

Giant ionic lattice

A regular three-dimensional structure made of alternating positive and negative ions held together by strong electrostatic attractions in all directions.

Metallic bonding

The electrostatic attraction between a lattice of positive metal ions and a 'sea' of mobile, delocalised electrons.

Volatility

A property describing how easily a substance evaporates, with volatile substances having low boiling points.

Relative atomic mass ($A_r$)

The average mass of an atom of an element compared with $\frac{1}{12}$ of the mass of an atom of carbon-12.

Relative molecular mass ($M_r$)

The sum of the relative atomic masses of all the atoms present in a molecular formula.

Mole

The amount of substance that contains the same number of specified particles as there are atoms in $12\,\text{g}$ of carbon-12 ($6.02 \times 10^{23}\,\text{particles}$).

Limiting reactant

The reactant that is completely consumed first in a chemical reaction, thereby determining and limiting the maximum amount of product formed.

Empirical formula

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

Molecular formula

The formula that indicates the actual number of atoms of each element present in a single molecule of a compound.

Diffusion

The net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient as a result of their random motion.

Brownian motion

The erratic, random zig-zag motion of microscopic visible particles suspended in a fluid caused by uneven bombardment by surrounding fluid molecules.

Retention factor ($R_f$)

In chromatography, the ratio of the distance moved by a substance to the distance moved by the solvent front, measured from the pencil baseline.

Acid

A substance that acts as a proton donor ($\text{H}^+$) in aqueous solution.

Base

A substance that acts as a proton acceptor and neutralises an acid.

Alkali

A soluble base that dissolves in water to produce hydroxide ions ($\text{OH}^-$).

Neutralisation

The reaction between an acid and a base to form a salt and water, represented fundamentally by the net ionic equation $\text{H}^+(aq) + \text{OH}^-(aq) \rightarrow \text{H}_2\text{O}(l)$.

Alloy

A mixture of a metal with one or more other elements, typically harder than pure metals because different-sized atoms distort regular metal layers.

Oxidation

The gain of oxygen or the loss of electrons by a chemical species.

Reduction

The loss of oxygen or the gain of electrons by a chemical species.

Electrolysis

The decomposition of an ionic compound, either molten or dissolved in aqueous solution, by the passage of an electric current.

Exothermic reaction

A chemical reaction that transfers thermal energy to the surroundings, causing the temperature of the surroundings to increase ($\Delta H < 0$).

Endothermic reaction

A chemical reaction that absorbs thermal energy from the surroundings, causing the temperature of the surroundings to decrease ($\Delta H > 0$).

Activation energy

The minimum amount of energy required by colliding particles for a chemical reaction to occur successfully.

Dynamic equilibrium

A condition in a closed system where the forward and reverse reactions occur at equal rates, resulting in constant concentrations of reactants and products.

Le Chatelier's principle

The rule stating that when a system at equilibrium is subjected to an external change in conditions, the equilibrium position shifts in a direction that opposes the change.

Catalyst

A substance that increases the rate of a chemical reaction without being consumed, by providing an alternative pathway with lower activation energy.

Hydrocarbon

An organic compound composed entirely of hydrogen and carbon atoms only.

Homologous series

A family of organic compounds with the same functional group, the same general formula, similar chemical properties, and consecutive members differing by a $-\text{CH}_2-$ unit.

Functional group

An atom or specific group of atoms in an organic molecule that determines its characteristic chemical properties and reactions.

Structural isomers

Compounds that share the same molecular formula but have different structural formulae due to different arrangements of their atoms.

Cracking

The thermal breakdown of long-chain hydrocarbons into shorter, more useful alkanes and alkenes using high temperatures and a catalyst.

Addition polymerisation

A reaction in which many unsaturated monomer molecules join together by the opening of their carbon-carbon double bonds to form a single long-chain polymer without any by-products.