OCR GCSE Chemistry A key terms

The ability of a material to let electric current pass through it.

A property of matter that may be positive, negative or neutral; opposite charges attract.

A conducting part of a cell through which electrons enter or leave the external circuit.

The decomposition of an ionic substance by passing a direct electric current through it while its ions are free to move.

A liquid or solution containing mobile ions that can carry electric charge between electrodes.

A negatively charged sub-atomic particle found in the region surrounding an atomic nucleus.

The arrangement of an atom’s or ion’s electrons in energy levels, often written as numbers such as 2,8,1.

The arrangement of an atom's electrons among its occupied energy levels or shells.

An allowed energy level at a particular distance from the nucleus in the Bohr model.

A force of attraction between particles or regions with opposite electric charges.

A substance containing only one type of atom, identified by its number of protons.

The release of radiation by matter.

The simplest whole-number ratio of atoms of each element in a compound.

A reaction direction that takes in energy from the surroundings.

A reaction that takes in energy from the surroundings, leaving products at a higher energy level than the reactants.

The point at which the indicator shows its first permanent colour change.

The point at which an indicator first shows the required permanent colour change.

A region around the nucleus in which electrons have a similar energy; also called an electron shell.

An individual object being counted, such as an atom, molecule, ion or formula unit.

A change to the environment caused by an activity or product, such as resource depletion, pollution or waste production.

A protein that acts as a catalyst in a biological system.

A mathematical statement showing that the expressions on its two sides have the same value.

The relative amounts of reactants and products present when a reversible reaction has reached equilibrium.

The theoretical point at which reactants have been mixed in exactly the proportions shown by the balanced equation.

An approximate value that is sufficiently close to show the correct size or scale.

More reagent than is needed to complete the initial reaction.

A reactant present in a greater amount than is required to react with the limiting reactant, so some remains when the reaction stops.