Term Definition

Acid dissociation constant, K a Ka = ¿¿

Acid-base pair A pair of two species that transform into each other by gain or loss of a proton.

Addition reaction A reactant is added to an unsaturated molecule to make a saturated molecule.

Adsorption The process by which a solid holds molecules of a gas or liquid or solute as a thin film on the surface of a solid or, more rarely, a liquid.

Alkali A base that dissolves in water forming OH−¿¿(aq) ions.

Bidentate The ligand can donate two lone pairs of electrons to the central metal ion to form two coordinate bonds.

Biodegradable polymer A polymer that breaks down completely into carbon dioxide and water.

Bronsted-Lowry acid A proton donor.

Bronsted-Lowry base A proton acceptor.

Buffer solution A mixture that minimises pH changes on addition of small amounts of acid or base.

Catalyst Increases the rate of a chemical reaction without undergoing any permanent change itself. Does this by providing an alternate route of lower activation energy.

Chemical shift, δ A scale that compares the frequency of an NMR absorption with the frequency of the reference peak for TMS at δ=0 ppm.

Chiral carbon A carbon atom attached to four different atoms or groups of atoms.

Chromatogram A visible record showing the result of separation of the components of a mixture by chromatography.

Complex ion A transition metal ion bonded to one or more ligands by coordinate bonds (dative covalent bonds).

Condensation reaction Two small molecules react together to form a larger molecule with the elimination of a small molecule such as water.

Coordination number The total number of coordinate bonds formed between a central metal ion and its ligands.

Curly arrow A symbol used in reaction mechanisms to show the movement of an electron pair in the breaking or formation of covalent bonds.

Degradable polymer A polymer that breaks down into smaller fragments when exposed to light, heat or moisture.

Delocalised electrons Shared between more than two atoms.

Dynamic equilibrium Exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction.

Electronegativity A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.

Electrophile An atom or group of atoms that is attracted to an electron rich centre, where it accepts a pair of electrons to form a new covalent bond.

Electrophilic substitution A type of substitution reaction in which an electrophile is attracted to an electron rich centre or atom, where it accepts a pair of electrons to form a new covalent bond.

End point The point in the titration at which there are equal concentrations of the weak acid and conjugate base forms of the indication.

Enthalpy change of atomisation The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state.

Entropy, S The quantitative measure of the degree of disorder in a system.

Equilibrium law For the equilibrium aA + bB ⇌ cC + dD, K c = [C ]c [D ]d

[A ]a[B ]b

Equivalence point The point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution.

Esterification The reaction of an alcohol with a carboxylic acid to produce an ester and water.

First electron affinity The enthalpy change accompanying the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.

First ionisation energy The enthalpy change accompanying the removal of one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Free energy change, ∆G The balance between enthalpy, entropy and temperature for a process: ∆G = ∆H - T∆S. A process can take place spontaneously when ∆G<0.

Functional group The part of an organic molecule responsible for its chemical reactions.

Half-life The time taken for the concentration of a reactant to reduce by half.Heterogeneous equilibrium An equilibrium in which species making up the reactants and products are in different physical states.

Homogenous equilibrium An equilibrium in which all the species making up the reactants and products are in the same physical state.

Hydrolysis A reaction with water or hydroxide ions that breaks a chemical compound into two compounds.

Initial rate of reaction The change in concentration of a reactant or product per unit time at the start of the reaction when t=0.

Intermediate A species formed in one step of a multi-step reaction that is used up in a subsequent step, and is not seen as either a reactant or a product of the overall equation.

Ionic product of water, Kw Kw = [H+¿(aq)¿][OH−¿(aq)¿], at 25degC, Kw = 1.00×10−14moldm−3

Isoelectric point The pH value at which the amino acid exists as a zwitterion.

K a Ka = 10−p Ka

Lattic enthalpy The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.

Lewis acid An electron-pair acceptor

Lewis base An electron-pair donor.

Ligand A molecule or ion that can donate a pair of electrons with the transition metal ion to form a coordinate bond.

Ligand substitution A reaction in which one ligand in a complex ion is replaced by another ligand.

Mobile phase The phase that moves in chromatography.

Neutralisation A chemical reaction in which an acid and a base react together to produce a salt and water.

Nucleophile An atom or group of atoms attracted to an electron deficient centre, where it donates a pair of electrons to form a new covalent bond.

Optical isomers (enantiomers) Stereoisomers that are non-superimposable mirror images of each other.

Order The power to which the concentration of the reactant is raised in the rate equation.

Overall order The sum of the individual orders.

Oxidation Loss of electrons, or an increase in oxidation number.

Peptide A compound made of amino acids linked by peptide bonds.

Pharmacological activity The beneficial or adverse effect of a drug on living matter.

Phase A physically distinctive form of a substance e.g. solid, liquid or gaseous.

Photodegradable polymer Synthetic polymers that break down when exposed to sunlight for prolonged periods.

pK a pK a = -log10 Ka

Rate constant, k The constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation.

Rate equation For reaction A + B → C, rate=k[A ]m[B ]n

Rate of reaction The change in concentration of a reactant or product per unit time.

Rate-determining step The slowest step in the reaction mechanism of a multi-step reaction.

Reaction mechanism A series of steps that together make up the overall reaction.

Redox reaction Both reduction and oxidation take place.

Reduction Gain of electrons, or a decrease in oxidation number.

Reflux The continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry.

Repeat unit The specific arrangement of atoms that occurs in the structure over and over again.

Retention time The time for a component to pass from the column inlet to the detector.

R fDistancemoved by componentDistancemoved by solvent front

Second electron affinity The enthalpy change accompanying the addition of one electron to each atom in one mole of gaseous 1- ions to form one mole of gaseous 2- ions.

Second ionisation energy The enthalpy change accompanying the removal of one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

Stability constant, K stabThe equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed with the same ion has undergone a ligand substitution.

Standard electrode potential The e.m.f. of a half cell compared with a standard hydrogen half cell, measured at 298 K with solution concentrations of 1 moldm−3

and a gas pressure of 100kPa.

Standard enthalpy change of formation

The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

Standard enthalpy change of hydration

The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions.

Standard enthalpy change of neutralisation, ΔH neut

The energy change that accompanies the neutralisation of an aqueous acid by an aqueous base to form one mole of H 2O (l) under standard conditions.

Standard enthalpy change of solution The enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions.

Standard entropy change of reaction, ΔS

The entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.

Stationary phase The phase that does not move in chromatography.

Stem The longest carbon chain present in an organic molecule.

Stereoisomers Species with the same structural formula but with a different arrangement of the atoms in space.

Stoichiometry The molar relationship between the relative quantities of substances taking part in a reaction.

Strong acid An acid that completely dissociates in solution.

Substitution reaction An atom or group of atoms is replaced with a different atom or group of atoms.

Suffix The part of the name added after the stem.

Transition element A d-block element that forms an ion with an incomplete d sub-shell.

Weak acid An acid that partially dissociates in solution.

Zwitterion A dipolar ionic form of an amino acid that is formed by the donation of a hydrogen ion from the carboxyl group to the amine group. There is no overall charge.