62 of the Chemistry glossary’s terms, each with the part of the syllabus where you first meet it.
The range, written as ± in the same unit as the value, within which the true value of a measurement is expected to lie, such as .
The lowest possible temperature, (), at which particles have their minimum possible kinetic energy.
A measure of how much light of a chosen wavelength a solution absorbs; in dilute solution it is proportional to the concentration of the absorbing species.
A continuous spectrum crossed by dark lines at the wavelengths absorbed by atoms as their electrons are promoted to higher energy levels.
How close a measured or calculated result is to the true or accepted value; systematic errors reduce accuracy.
Describes a molecule that can be superimposed on its mirror image, such as one with no chiral carbon; achiral compounds are not optically active.
The deposition of acids formed from sulfur oxides and nitrogen oxides in rain, snow and fog (wet) or as gases and particles (dry). Acid rain has a pH below 5.6.
The equilibrium constant for the ionization of a weak acid in water,
A weak acid, HInd, whose un-ionized form and conjugate base have different colours; it changes colour over a pH range of roughly
A buffer made of a weak acid and a salt of its conjugate base, such as ethanoic acid with sodium ethanoate; its pH is below 7.
An oxide, usually covalent and of a non-metal, that reacts with bases to form a salt and water; if soluble it gives an acidic solution, as does.
One of the elements actinium to lawrencium in period 7. In the data booklet actinium sits in group 3 and thorium to lawrencium form the second f-block row printed below the main table.
The minimum energy that colliding particles need for a reaction to occur; on an energy profile, the energy difference between the reactants and the transition state.
An electrode that takes part in the electrode reaction, such as a copper anode that is oxidized and dissolves during electrolysis.
A polymer formed by addition polymerization of monomers with a C=C double bond, such as poly(ethene), PVC and PTFE.
A reaction in which many monomers containing a C=C double bond join into one long saturated chain, with no other product, so the atom economy is 100 %.
A reaction in which two reactants combine to form a single product, as when a molecule adds across the double bond of an alkene.
A single species formed when a Lewis acid and a Lewis base combine through a coordination bond without any atoms being lost, such as
A compound containing a hydroxyl group bonded to a saturated carbon atom, general formula
A compound with a carbonyl group at the end of a carbon chain, –CHO, general formula
A base that dissolves in water to form hydroxide ions, , such as sodium hydroxide or aqueous ammonia. Every alkali is a base, but insoluble bases such as are not alkalis.
An element of group 1 other than hydrogen (lithium, sodium, potassium, rubidium, caesium, francium): a soft, reactive metal with one valence electron that forms ions.
An element of group 2 (beryllium, magnesium, calcium, strontium, barium, radium): a reactive metal with two valence electrons that forms ions.
A saturated hydrocarbon with only C–C and C–H single bonds and the general formula
A hydrocarbon containing a C=C double bond, general formula
The functional group –O–R, an oxygen atom bonded to two carbon atoms; it defines the ethers.
A group formed by removing one H atom from an alkane,
A hydrocarbon containing a C≡C triple bond, general formula
One of two or more structural forms of the same element in the same physical state, such as diamond, graphite, graphene and fullerenes for carbon; allotropes differ in bonding and so in properties.
A mixture of a metal with one or more other elements (usually metals), made by melting them together; different-sized atoms disrupt the layers, so alloys are usually harder than the pure metal.
A helium nucleus, , of two protons and two neutrons, emitted by some radioactive nuclei; used in the gold-foil experiment.
A compound containing an amido group, –CONH₂, such as ethanamide,
The group that joins the residues of an acid and an amine in an amide or a polyamide.
The functional group –CONH₂ (or –CONH– when the N carries a carbon group): a nitrogen atom bonded to the carbon of a C=O; it defines the amides.
A compound containing an amino group, such as ethylamine,
An organic molecule with both an amino group () and a carboxyl group (); amino acids are the monomers of proteins.
The functional group –NH₂ (or –NHR, –NR₂) bonded to carbon; it defines the amines.
A measure of the number of specified particles in a sample, symbol , measured in moles.
Able to act as both a Brønsted–Lowry acid and a Brønsted–Lowry base, by donating or accepting a proton; examples are ,
Able to react both as an acid and as a base. Aluminium oxide,
The substance or solution being analysed in a titration, usually measured into the conical flask with a pipette.
Containing no water; an anhydrous salt is the form left when the water of crystallization has been removed, such as white .
A negatively charged ion, with more electrons than protons; non-metals form anions by gaining electrons.
The electrode at which oxidation takes place. In a voltaic cell (including a fuel cell) it is the negative electrode.
The insoluble residue of less reactive metals, such as silver, gold and platinum, that collects beneath the anode during electrolytic refining.
A base taken to neutralize excess hydrochloric acid in the stomach, such as calcium carbonate, magnesium hydroxide or sodium hydrogencarbonate.
A compound that contains a benzene ring, such as methylbenzene,
The equation , which describes how the rate constant depends on temperature and activation energy. Its linear form is
The constant in the Arrhenius equation, which takes into account the frequency of collisions with the proper orientation. It has the same units as .
A graph of against : a straight line with gradient and intercept
The molar mass of the desired product as a percentage of the total molar mass of all the reactants in the balanced equation; it measures how much of the reactants' mass can end up in the desired product.
The number of protons in the nucleus of an atom, symbol ; it identifies the element and gives its position in the periodic table.
A region of space around the nucleus with a high probability of finding an electron; each orbital holds a maximum of two electrons of opposite spin.
Half the distance between the nuclei of two neighbouring atoms of the same element bonded together. It decreases across a period and increases down a group.
Electrons occupy the orbitals of lowest available energy first; up to Z = 36 the order of filling is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p.
The reaction in which water molecules transfer protons to each other,
The mean bond enthalpy of a particular bond taken over a range of compounds that contain it, as listed in the data booklet.
The mean of the electronegativities of two bonded elements, ; on the bonding triangle a low value indicates metallic bonding and a high value covalent bonding.
The change in concentration (or another measured quantity) divided by the time interval over which it occurs; the gradient of a chord on a graph against time.
The number of elementary entities in one mole, (fixed exactly at
Equal volumes of all gases, measured at the same temperature and pressure, contain equal numbers of molecules.
One of the two positions on the vertical axis of a trigonal bipyramid, 180° apart, each with three neighbouring electron domains at 90°.