Gce O Level Chemistry Definitions

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Kinetic particle theory

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All matter is made up of tiny particles and these particles are in constant motion.

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Diffusion

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The movement of particles from a region of higher concentration to a region of lower concentration.

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Pure substance

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Made up one single element or compound. It is not mixed with any other substances.

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Filtration

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Used to separate insoluble particles from a liquid.

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Evaporation to dryness

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Used to obtain a soluble solid from a solution by heating the solution until all the water has boiled off.

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Crystallisation

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Used for obtaining a pure solid sample from its solution.

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Sublimation

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Used to separate a solid that sublimes from one that does not.

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Magnet

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Used to separate a magnetic substance from a non-magnetic substance.

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Simple distillation

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Used to separate a pure solvent from a solution.

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Separating funnel

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Used to separate immiscible liquids.

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Fractional distillation

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Used to separate a mixture of miscible liquids with different boiling points.

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Chromatography

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The method of separating two or more components that dissolve in the same solvent.

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Element

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

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Atoms

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The smallest particles of an element that have the chemical properties of that element.

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Molecule

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A group of two or more atoms that are chemically combined.

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Compound

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A pore substance containing two or more elements that are chemically combined in a fixed ratio.

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Mixture

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Made up of two or more substances that are not chemically combined.

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Proton number

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Refers to the number of protons in the atom

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Nucleon number

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The total number of protons and neutrons in the atom.

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Isotopes

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

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Ionic bonds

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The strong electrostatic forces of attraction between positive and negative ions.

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Covalent bond

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A bond formed by the sharing of electrons between two atoms.

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Metallic bond

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The force of attraction between positive metal ions and the 'sea of mobile electrons'.

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Relative atomic mass

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The average mass of one atom of that element compared to 1/12 of the mass of one carbon-12 atom.

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Relative molecular mass

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The average mass of one molecule of that element or compound compared to 1/12 of the mass of one carbon-12 atom.

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Avogadro's constant

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6 x 10^23

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Concentration

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The amount of sole dissolved in a unit volume of the solution.

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Acid

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A substance that produces hydrogen ions, H+, in aqueous solution.

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Base

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

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Alkali

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A substance that produces hydroxide ions, OH-, in aqueous solution.

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Alloy

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A mixture of a metal with one or a few other elements.

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Electrolysis

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The process of using electricity to break down or decompose a compound.

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Electroplating

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The process of depositing a layer of metal on another substance using electrolysis.

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Exothermic reaction

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A reaction in which heat is given out to the surroundings.

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Endothermic reaction

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A reaction in which heat is absorbed from the surroundings.

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Enthalpy change (∆H)

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Represents the difference in energy content of the reactants and products.

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Activation energy

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The minimum amount of energy that reactant particles must possess n order for a chemical reaction to occur.

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Catalyst

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A substance which increases the speed of a chemical reaction and remains chemically unchanged at the end of the reaction.

They provide an alternative pathway and lower activation energy.

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Air pollution

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The condition in which air contains a high concentration of chemicals that may harm living things of damage non-living things.

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Acid rain

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Formed when acidic air pollutants such as sulphur dioxide and nitrogen dioxide react with water in the atmosphere.

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Chlorofluorocarbons

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Compounds containing the elements carbon, fluorine and chlorine.

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Carbon cycle

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The mechanisms that maintains the level of carbon dioxide in the atmosphere.

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Global warming

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The increase in the Earth' average temperature due to the build-up of greenhouse gases in the atmosphere.

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Homologous seres

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A family of organic compounds with the same functional group and similar chemical properties.

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Functional group

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An atom or group that gives a molecule is characteristic properties.

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Petroleum

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A naturally occurring mixture of hydrocarbons (mainly alkanes).

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Alkanes

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Homologous series of hydrocarbons that contain only C-C single covalent bonds.

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Alkenes

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Homologous series of hydrocarbons that contain one or more C=C double bonds.

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Cracking

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The breaking down of long chain hydrocarbons into smaller molecules.

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Alcohols

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A homologous series of organic compounds which contains the hydroxyl (-OH) functional group.

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Carboxylic acids

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A homologous series of organic aide which have the carboxyl (-COOH) functional group.