41 of the Chemistry glossary’s terms, each with the part of the syllabus where you first meet it.
A mixture of equal amounts of the two enantiomers of a chiral compound; it is optically inactive because their rotations of plane-polarized light cancel.
A species with an unpaired electron, shown with a dot, for example ; radicals are formed by homolytic fission and are usually very reactive.
An isotope with an unstable nucleus that decays, emitting radiation, such as carbon-14.
An unpredictable error that makes repeated measurements scatter either side of the true value; its effect is reduced by repeating measurements and taking a mean.
The constant of proportionality, , in the rate equation. It is fixed for a given reaction at a given temperature, increases with temperature, and its units depend on the overall order.
An equation, found by experiment, that links the rate of a reaction to the concentrations of the species that affect it, in the form rate .
The change in concentration of a particular reactant or product per unit time, in ; it is always positive.
The slowest elementary step in a reaction mechanism. It has the largest activation energy and determines the rate of the whole reaction.
Measurements exactly as read from the instruments, before any calculation, recorded with their units and uncertainties.
The x-axis of an energy profile, representing the progress of a reaction from reactants to products; it has no units or scale.
A species formed in one elementary step of a mechanism and used up in a later step. It sits in an energy minimum between two transition states and does not appear in the overall equation.
The sequence of elementary steps by which reactants are converted into products. The steps must add up to the overall stoichiometric equation.
The value obtained by substituting the concentrations present at any moment into the equilibrium constant expression; the mixture reacts forwards if and backwards if .
A list of metals in order of how easily they are oxidized to their positive ions; a metal higher in the series displaces a lower one from a solution of its ions.
An actual gas, whose particles have a finite volume and attract one another; it deviates from ideal behaviour most at high pressure and low temperature.
Purification of a solid by dissolving it in the minimum volume of hot solvent, cooling so that the pure compound crystallizes while impurities stay dissolved, then filtering, washing with cold solvent and drying.
The oxidized and reduced forms of one species that are converted into each other by gaining or losing electrons, such as or
A reaction in which oxidation and reduction occur together: one species loses electrons (its oxidation state increases) and another gains them (its oxidation state decreases).
A titration in which the titrant is an oxidizing or reducing agent, such as acidified potassium manganate(VII) used to find the amount of iron(II) in a sample.
A species that reduces another species by donating electrons to it; the reducing agent is itself oxidized.
The gain of electrons by a species, or a decrease in its oxidation state.
A half-cell of known, stable potential against which the potentials of other half-cells are measured; the standard hydrogen electrode is the primary reference.
Continuous boiling of a reaction mixture with a vertical condenser above it, so that vapours condense and return to the flask; it allows prolonged heating without loss of volatile substances.
The weighted mean mass of the atoms of an element, taking into account the abundance of each isotope, compared with one-twelfth of the mass of an atom of carbon-12. Symbol ; it has no units.
The sum of the relative atomic masses of all the atoms in the formula of a substance. Symbol ; it has no units.
The mass of an atom of one isotope relative to one-twelfth of the mass of an atom of carbon-12; very close to its mass number.
The relative formula mass of a substance made of molecules: the sum of the relative atomic masses of the atoms in one molecule. It has no units.
A comparison of substances by their potential energy: the one lower in energy is more stable. Products more stable than reactants means the reaction is exothermic.
An energy source that is replenished naturally on a human timescale, such as solar, wind, hydroelectric, tidal and geothermal energy and biofuels.
The smallest section of a polymer chain that repeats along its length; it is drawn in brackets with continuation bonds through the brackets and outside.
A single, focused question that an investigation sets out to answer, naming the independent variable and its range, the dependent variable and how it is measured, and the chemical system studied.
The insoluble solid left on the filter paper after filtration.
A number from 1 to 7 printed on a plastic item, usually inside a recycling symbol, that identifies the polymer it is made of so that plastics can be sorted for recycling.
The smallest change in a quantity that an instrument can show, such as 0.01 g on a balance or 0.1 °C on a digital thermometer.
The real structure of a species with resonance: a single structure that is an average of its resonance structures, with delocalized electrons and equivalent bonds of intermediate order.
One of two or more valid Lewis formulas for a species that differ only in the positions of electrons, not of atoms; they are joined by a double-headed arrow, ↔.
The inability of the groups on two bonded atoms to turn relative to each other, because the atoms are joined by a double bond (rotation would break the π bond) or are part of a ring.
In chromatography, the distance moved by a component divided by the distance moved by the solvent front, both measured from the baseline; always less than 1.
A reaction in which the products can react to re-form the original reactants; shown with the symbol .
A written review, made before practical work, of the hazards of each substance and procedure, the precautions that reduce the risk, and how waste will be disposed of.
The corrosion of iron or steel in the presence of both oxygen and water, forming hydrated iron(III) oxide,