IGCSE Chemistry: Key Vocabulary Flashcards (Video Notes)

Vocabulary-style flashcards covering key terms from the notes.

H2O

Water; chemical formula for the compound water; liquid at room temperature; universal solvent.

Elements

Substances made of only one type of atom.

Mixtures

Substances made of two or more elements or compounds not chemically bonded.

Pure substance

A substance with a fixed composition; either an element or a compound.

Solid

State of matter with a definite shape and volume; particles vibrate and are tightly held together.

Liquid

State of matter with a definite volume but no fixed shape; particles flow past each other.

Gas

State of matter with no fixed shape or volume; particles move freely and are far apart.

Melting point

Temperature at which a solid changes into a liquid.

Boiling point

Temperature at which a liquid changes into a gas; at external pressure.

Sublimation

Solid changing directly to gas without becoming liquid.

Deposition

Gas changing directly to solid; desublimation.

Diffusion

Spread of particles from an area of higher concentration to lower concentration.

Ionic bond

Electrostatic attraction between oppositely charged ions in a compound.

Covalent bond

Bond formed by sharing electron pairs between atoms.

Metallic bond

Bonding between metal ions and a sea of delocalised electrons.

Diamond

Giant covalent structure of carbon; very hard; rigid network of bonds.

Graphite

Carbon allotrope with layered structure; conducts electricity; slippery.

Silicon dioxide

SiO2; giant covalent network; hard with high melting point.

Allotrope

Different structural forms of the same element with different properties.

Isotopes

Atoms of the same element with the same proton number but different neutron numbers.

Relative atomic mass (Ar)

Weighted average mass of an element’s atoms relative to C-12 = 12.

Avogadro constant (NA)

6.02 × 10^23 particles per mole.

Mole

Amount of substance containing NA particles.

Molar volume

Volume occupied by one mole of a gas at a given temperature and pressure (≈24 dm^3 at room temp and pressure).

Concentration

Amount of solute per unit volume of solution (mol/dm^3).

Empirical formula

Simplest whole-number ratio of atoms in a compound.

Molecular formula

Actual numbers of each type of atom in a molecule.

Oxidation

Loss of electrons; increase in oxidation state; often involves gain of oxygen.

Reduction

Gain of electrons; decrease in oxidation state; often involves loss of oxygen.

Oxidation state

Formal charge (oxidation number) assigned to atoms in compounds.

Redox

Oxidation–reduction reaction; electron transfer between species.

Half-reaction

One part of a redox equation showing either oxidation or reduction.

Electrolyte

Ionic substance that conducts electricity when molten or dissolved.

Cathode

Electrode at which reduction occurs; in electrolysis, typically the negative electrode.

Anode

Electrode at which oxidation occurs; in electrolysis, typically the positive electrode.

Electrolysis

Decomposition of an ionic compound by passing an electric current.

Oxidising agent

Substance that oxidises another substance and is itself reduced.

Reducing agent

Substance that reduces another substance and is itself oxidised.

Activation energy

Minimum energy required for particles to react on collision.

Enthalpy

Heat content change of a system; symbol AH.

Exothermic

Reactions that release heat to the surroundings.

Endothermic

Reactions that absorb heat from the surroundings.

Rate of reaction

Speed at which reactants are used up or products formed.

Collision theory

Reactions occur when particles collide with sufficient energy and proper orientation.

Temperature

Measure of the average kinetic energy of particles; affects reaction rate.

Pressure

Force per unit area; for gases, higher pressure increases collision frequency.

Surface area

Area of a solid's surface; larger area increases rate of reaction for solids.

Catalyst

Substance that speeds up a reaction without being consumed; lowers activation energy.

Enzymes

Biological catalysts made of proteins that speed up reactions in organisms.

Equilibrium

Dynamic state where forward and reverse reaction rates are equal and concentrations are constant.

Le Châtelier’s principle

If a system at equilibrium is disturbed, it shifts to counteract the change.

Haber process

Industrial synthesis of ammonia from N2 and H2 using iron catalyst.

Ammonia

NH3; product of the Haber process.

Nitrogen

N2; diatomic atmospheric gas.

Hydrogen

H2; diatomic gas; fuel and reactant in many processes.

Acid

Substance that donates protons; turns litmus red.

Base

Substance that accepts protons; turns litmus blue; typically basic.

Salt

Product of an acid–base neutralisation; ionic compound.

Neutralisation

Reaction of an acid with a base to form a salt and water.

Indicator

Substance that changes colour to show pH or endpoint of a titration.

Water of crystallisation

Water molecules chemically bound within a crystalline salt.

CuSO4·5H2O

Copper(II) sulfate pentahydrate; blue hydrated salt used in tests for water.

Anhydrous cobalt(II) chloride test

CoCl2 blue when dry; turns pink in the presence of water.

Solubility

Maximum amount of solute that can dissolve in solvent at a given temperature.

Precipitation

Formation of an insoluble solid from ions in solution.

Hydrated salt

Salt containing water of crystallisation.

Group 1 (alkali metals)

Li, Na, K; highly reactive metals that react with water to produce hydroxides and hydrogen.

Halogens

Group 7 nonmetals; diatomic; highly reactive; reactivity decreases down the group.

Noble gases

Group 0; inert, monatomic gases with full outer electron shells.

Transition metals

Metals with variable oxidation states; form colored compounds and useful catalysts.

Valency

Number of electrons an atom loses, gains, or shares to form a compound.

Corrosion

Deterioration of metals due to reaction with environment (e.g., rusting).

Sacrificial protection

Protecting a metal by attaching a more reactive metal that corrode instead.

Galvanising

Coating iron with zinc to prevent corrosion.

Aluminium oxide layer

Thin protective oxide layer on aluminium reducing further corrosion.

Rust

Hydrated iron(III) oxide; corrosion product of iron and water/oxygen.

Blast furnace

Industrial reactor for extracting iron; reduction of hematite with CO; limestone removes silica.

Slag

Impurity waste (calcium silicate) formed during iron extraction.

Carbon monoxide

CO; toxic gas produced by incomplete combustion; reducing agent in metallurgy.

Carbon dioxide

CO2; gas from combustion; greenhouse gas; forms carbonic acid in water.

Oxygen

O2; essential for combustion and respiration; diatomic gas.

Greenhouse gases

Gases that trap heat in the atmosphere, contributing to global warming.

Catalytic converter

Device using catalysts (Pt/Pd/Rh) to convert pollutants in exhaust gases.

Photosynthesis

Process by which plants convert CO2 and water to glucose and O2 using light.

Carbon cycle

Movement of carbon through air, water, living organisms, and rocks.

Fractional distillation

Separation of mixtures by boiling points in a column.

Cracking

Breaking long-chain hydrocarbons into smaller ones using heat, pressure, and catalysts.

Homologous series

Family of organic compounds with the same functional group and general formula.

Functional group

Specific atom group that determines chemical properties of a molecule.

Alkanes

Saturated hydrocarbons with C-C single bonds; general formula CnH2n+2; burn cleanly.

Alkenes

Unsaturated hydrocarbons with C=C; general formula CnH2n; undergo addition reactions.

Alkynes

Unsaturated hydrocarbons with C≡C triple bond; general formula CnH2n-2.

Addition polymerisation

Polymer formation from monomers with C=C bonds via addition reactions.

Condensation polymerisation

Polymer formation releasing a small molecule (often water) and joining monomers.

Nylon

Synthetic polyamide formed from diamine and dicarboxylic acid.

Polyester (Terylene)

Polyester made from diol and dicarboxylic acid with ester linkages.

Monomer

Small molecule that can join to form a polymer.

Polymer

Large molecule formed by linking many monomers.

Starch

Natural polysaccharide; glucose polymer used for energy storage in plants.

Cellulose

Natural polysaccharide; glucose polymer; structural component of plants.