24 of the Chemistry glossary’s terms, each with the part of the syllabus where you first meet it.
One of the elements lanthanum to lutetium in period 6. In the data booklet lanthanum sits in group 3 and cerium to lutetium form the first f-block row printed below the main table.
The standard enthalpy change when one mole of a solid ionic compound is separated into its gaseous ions, e.g. ; it is positive and measures the strength of the ionic bonding.
Energy cannot be created or destroyed, only transferred or converted from one form to another, so the total energy of a system and its surroundings is constant.
In a chemical reaction, mass is neither created nor destroyed: the total mass of the products equals the total mass of the reactants, because atoms are only rearranged.
If a system at equilibrium is subjected to a change in conditions, the position of equilibrium shifts in the direction that partly opposes the change.
A secondary cell with a lead negative electrode and a lead(IV) oxide positive electrode in sulfuric acid; both electrodes form lead(II) sulfate on discharge, and each cell gives about 2 V.
The atom or group that leaves a substrate in a substitution reaction, taking the bonding pair with it, such as a halide ion from a halogenoalkane.
An electron-pair acceptor. Examples include ,
An electron-pair donor: a species with a lone pair that it shares to form a coordination bond, such as ,
A diagram of a covalently bonded species that shows all its valence electrons: bonding pairs between the atoms and lone pairs on the atom that owns them, as dots, crosses or lines.
A molecule or ion with a lone pair of electrons that forms a coordination bond to a central metal ion, such as ,
A reaction in which the ligands of a complex ion are replaced by other ligands, such as
A restriction on how widely the conclusion of an investigation applies, set by the range of the data, the system studied or the assumptions made.
The reactant that is completely used up in a reaction, so it determines the amount of product formed; the others are in excess.
The straight line or smooth curve drawn as close as possible to all the plotted points, with the points scattered evenly either side of it.
A spectrum containing only certain separate wavelengths, seen as sharp lines; the pattern of lines is characteristic of each element.
Rearranging a non-linear relationship so that a graph of two processed quantities should be a straight line, such as plotting against for the Arrhenius equation.
A value of a quantity taken from a reliable published source, such as a data booklet or a data table, used to judge the accuracy of an experimental result.
A secondary cell in which lithium ions move through an organic electrolyte between a graphite electrode and a metal oxide electrode such as ; it gives about 3.7 V.
A number in a name that gives the position of a functional group, double bond or substituent on the parent chain, as the 2 in propan-2-ol.
A scale on which the logarithm of a quantity is plotted, so that equal steps represent equal factors (such as ×10); used for data spanning several orders of magnitude, such as ionization energies.
An attraction between a temporary dipole and the dipole it induces in a neighbouring particle; it acts between all molecules and increases with the number of electrons and the contact area.
A pair of valence electrons that belongs to one atom only and is not shared in a bond.
The shine of a freshly cut or polished metal surface, which reflects most visible light falling on it.