Edexcel GCSE Chemistry key terms

The proportion of a sample made up of a particular isotope, often expressed as a percentage.

The average mass of an atom of an element compared with one-twelfth of the mass of a carbon-12 atom.

The weighted mean mass of an atom of an element relative to one-twelfth of the mass of a carbon-12 atom; it takes account of the relative abundances of the element’s isotopes.

The charge of a particle expressed by comparison with the magnitude of the charge on a proton.

The sum of the relative atomic masses of all the atoms represented in a chemical formula. It has no unit.

The sum of the relative atomic masses of all the atoms represented by a chemical formula; it has no unit.

A particle’s mass compared with an agreed reference mass; it allows the very small masses of subatomic particles to be compared conveniently.

The total relative mass of all the atoms in a molecule, compared with one-twelfth of the mass of a carbon-12 atom; it has no unit.

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

The relative mass of the particle being counted, found from the relative atomic masses of the atoms in its formula. It has no unit.

A selected part of a repeating structure which can be continued to represent more of the structure.

The smallest section of a polymer chain that occurs repeatedly along the chain.

The smallest section of a polymer chain that repeats; it is shown in square brackets with continuation bonds and an $n$ outside.

The risk that remains after control measures have been put in place.

The solid left on the filter paper after filtration.

How strongly a metal opposes being oxidised; a metal with greater resistance is less easily oxidised.

The smallest change in a quantity that a measuring instrument can display.

The reaction in the direction that converts the products back into the original reactants.

A reversible reaction is one in which products can react to form the original reactants.

The distance travelled by a substance divided by the distance travelled by the solvent front, both measured from the baseline.

The possibility that something will cause harm, taking account of both the potential harm and exposure to it.

A systematic process of identifying hazards, judging their risks and selecting measures that reduce those risks.

The usual temperature of the surroundings; in this context it is about 20 °C.

The usual conditions under which the GCSE molar gas volume is used, commonly taken as $20\,^{\circ}\text{C}$ and a pressure of one atmosphere.

Room temperature and pressure, the conditions at which the molar gas volume used in these calculations is $24\ \mathrm{dm^3\,mol^{-1}}$.

The corrosion of iron when it reacts in the presence of both oxygen and water.

Protection of iron by a more reactive metal that oxidises in preference to the iron.