39 of the Chemistry glossary’s terms, each with the part of the syllabus where you first meet it.
A method in which a known excess of a reagent is added to a sample and the amount left over is found by titration; the amount that reacted with the sample is found by difference.
Approach of a nucleophile to a carbon atom from the side directly opposite the leaving group, as in the mechanism.
In a reversible reaction, the reaction from right to left as the equation is written, turning products back into reactants.
The equilibrium constant for the reaction of a weak base with water,
The tallest peak in a mass spectrum, from the most abundant ion, assigned a relative abundance of 100.
A buffer made of a weak base and a salt of its conjugate acid, such as ammonia with ammonium chloride; its pH is above 7.
An oxide, usually ionic and of a metal, that reacts with acids to form a salt and water; if soluble it gives an alkaline solution, as does.
A vibration in which the angle between two bonds increases and decreases.
The way assessment criteria are applied: the marker chooses the level whose descriptor fits the work as a whole most fairly, even if not every point of it is met.
Describes an elementary step in which two particles collide and react (molecularity 2).
An ionic compound of only two elements, a metal and a non-metal, named with the cation first and the anion ending in "-ide", such as sodium chloride.
Able to be broken down into simpler substances by microorganisms in the environment.
A fuel similar to diesel, made by reacting vegetable oils or waste cooking oil with methanol to form smaller ester molecules.
Ethanol made by the fermentation of sugars from crops such as sugar cane, maize or sugar beet, used as a fuel on its own or blended with petrol.
A fuel produced from recently living material (biomass), whose carbon was fixed from the atmosphere by photosynthesis over a short period.
A fuel gas, mainly methane and carbon dioxide, produced by bacteria breaking down manure, sewage or food waste in the absence of oxygen.
One of the four regions of the periodic table (s, p, d and f), named after the sublevel that receives the last electron in the Aufbau order.
Vaporization throughout a liquid, with bubbles of vapour forming, at the temperature where the vapour pressure of the liquid equals the external pressure.
The temperature at which a liquid boils at a given external pressure; data tables quote it at 101.325 kPa.
A calorimeter in which a sample burns completely in pure oxygen inside a sealed steel vessel immersed in insulated water, giving accurate enthalpies of combustion.
The angle between two bonds from the same central atom, such as 104.5° for H–O–H in water.
The straight line joining the nuclei of two bonded atoms.
The separation of charge along a polar covalent bond, shown with partial charges or with an arrow pointing to the atom.
The energy needed to break one mole of a particular covalent bond in gaseous molecules to form gaseous atoms; always positive.
The distance between the nuclei of two covalently bonded atoms; more shared pairs between the same two atoms give a shorter bond.
The number of shared electron pairs between two bonded atoms (1 single, 2 double, 3 triple); in a resonance hybrid it can be fractional, such as 1.5 in benzene.
The idea that bonding changes gradually from covalent, through polar covalent, to ionic (and from covalent to metallic) rather than falling into separate categories; most real bonds have mixed character.
A pair of electrons shared between two atoms in a covalent bond.
A triangular diagram (in the data booklet) that classifies the bonding in an element or binary compound as ionic, polar covalent, covalent or metallic by plotting the electronegativity difference of its two elements against their average electronegativity.
An energy cycle for the formation of an ionic compound from its elements by way of gaseous atoms and gaseous ions, used to find a lattice enthalpy or another unknown term.
A concentrated aqueous solution of sodium chloride, electrolysed in industry to make chlorine, hydrogen and sodium hydroxide.
Breaking or shattering when struck rather than bending; ionic solids are brittle because a shifted layer brings ions of the same charge together and they repel.
An orange solution of bromine in water used to test for C=C double bonds: an alkene decolourizes it rapidly, even in the dark, while an alkane does not.
A species that donates a proton, , to another species in a reaction.
A species that accepts a proton, , from another species; it needs a lone pair of electrons to bond to the proton.
The amount of acid or alkali a buffer can absorb before its pH changes significantly; it is larger for more concentrated buffers and falls when a buffer is diluted.
The flat part of a pH curve, before equivalence for a weak acid titrated with a strong base, where both the weak acid and its conjugate base are present and the pH changes only slowly.
A solution that resists a change in pH when small amounts of acid or alkali are added; it contains a weak acid and its conjugate base, or a weak base and its conjugate acid.
A substance formed in a reaction alongside the desired product; unless a use is found for it, it is waste.