7/30/2019 Chemistry Glossary for A2

1/21

Chemistry Glossary for A2.

Acid dissociation constant, Ka

Acidbase pair

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

Activation energy

The minimum energy required to start a reaction by the breaking of bonds.

Addition polymer

A very long molecular chain, formed by repeated addition reactions of manyunsaturated alkene molecules (monomers).

Addition reaction

A reaction in which a reactant is added to an unsaturated molecule to make asaturated molecule.

Adsorption

The process that occurs when a gas, liquid or solute is held to the surface of a solidor, more rarely, a liquid.

Alicyclic hydrocarbonA hydrocarbon with carbon atoms joined together in a ring structure.

Aliphatic hydrocarbon

A hydrocarbon with carbon atoms joined together in straight or branched chains.

Alkali

A type of base that dissolves in water to form hydroxide ions, OH(aq) ions.

Alkanes

7/30/2019 Chemistry Glossary for A2

2/21

The homologous series with the general formula: CnH2n+2.

Alkyl group

An alkane with a hydrogen atom removed, e.g. CH3, C2H5; any alkyl group is often

shown as R.

Amount of substance

The quantity whose unit is the mole. Chemists use amount of substance as ameans of counting atoms.

Anhydrous

A substance that contains no water molecules.

Anion

A negatively charged ion.

Atom economy

Atomic (proton) number

The number of protons in the nucleus of an atom.

Atomic orbital

A region within an atom that can hold up to two electrons with opposite spins.

Average bond enthalpy

The average enthalpy change that takes place when breaking by homolytic fission1mol of a given type of bond in the molecules of a gaseous species.

Avogadros constant, NA

The number of atoms per mole of the carbon-12 isotope

(6.02 1023mol1).Biodegradable substance

A substance that is broken down naturally in the environment by other livingorganisms.

7/30/2019 Chemistry Glossary for A2

3/21

Biodegradable polymer

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

Boltzmann distribution

A diagram showing the distributionof energies of the molecules at a particulartemperature.

Bond dissociation enthalpy

The enthalpy change that takes place when breaking by homolytic fission 1mol of agiven bond in the molecules of a gaseous species.

BrnstedLowry acid

A species that is a proton, H+, donor.

BrnstedLowry base

A species that is a proton, H+, acceptor.

Buffer solution

A system that minimises pH changes on addition of small amounts of an acid or abase.

Carbanion

An organic ion in which a carbon atom has a negative charge.

Carbocation

An organic ion in which a carbon atom has a positive charge.

Catalyst

A substance that increases the rate of a chemical reaction without being used up inthe process.

Cation

A positively charged ion.

Chemical shift

A scale that compares the frequency of an NMR absorption with the frequency of the

reference peak of TMS at = 0ppm.

Chiral carbon

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

7/30/2019 Chemistry Glossary for A2

4/21

Chromatogram

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

chromatography.

cistransisomerism

A special type ofE/Zisomerism in which each carbon of the C=C double bondcarries the same atom or group: the cisisomer (Zisomer) has that group on eachcarbon on the same side; the transisomer (Eisomer) has that group on each carbonon different sides.

Complex ion

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

Concentration

The amount of solute, in mol, per 1dm3 (1000cm3) of solution.

Condensation reaction

A reaction in which two small molecules react together to form a larger molecule with

the elimination of a small molecule such as water.

Conjugate acid

A species formed when a proton is added to a base.

Conjugate base

A species formed when a proton is added to an acid.

Coordinate bondA shared pair of electrons in which the bonded pair has been provided by one of thebonding atoms only; also called a dative covalent bond.

Coordination number

The total number of coordinate bonds formed between the central metal ion and anyligands.

Covalent bond

A bond formed by a shared pair of electrons.

7/30/2019 Chemistry Glossary for A2

5/21

Cracking

The breaking down of long-chained saturated hydrocarbons to form a mixture of

shorter-chained alkanes and alkenes.

Curly arrow

A symbol used in reaction mechanisms to show the movement of an electron pairduring the breaking or formation of a covalent bond.

Dative covalent

A shared pair of electrons in which the bonded pair has been provided by one of thebonding atoms only; also called a coordinate bond.

Degradable polymer

A polymer that breaks down into smaller fragments when exposed to light, heat ormoisture.

Dehydration

An elimination reaction in which water is removed from a saturated molecule to makean unsaturated molecule.

Delocalised electrons

Electrons that are shared between more than two atoms.

Dipoledipole force

An attractive force between permanent dipoles in neighbouring polar molecules.

Displacement reaction

A reaction in which a more reactive element displaces a less reactive element froman aqueous solution of its ions.

Displayed formula

A formula showing the relative positioning of all the atoms in a molecule and thebonds between them.

Disproportionation

The oxidation and reduction of the same species in a redox reaction.

7/30/2019 Chemistry Glossary for A2

6/21

Dynamic equilibrium

The equilibrium that exists in a closed system when the rate of the forward reaction

is equal to the rate of the reverse reaction.

E/Zisomerism

A type of stereoisomerism in which different groups attached to each carbon of aC=C double bond may be arranged differently in space because of the restrictedrotation of the C=C bond.

(First) electron affinity

The enthalpy change required to add one electron to each atom in one mole ofgaseous atoms to form one mole of gaseous 1 ions.

(Second) electron affinity

The enthalpy change required to add one electron to each ion in one mole ofgaseous 1 ions to form one mole of gaseous 2 ions.

Electron shielding

The repulsion between electrons in different inner shells. Shielding reduces the net

attractive force from the positive nucleus on the outer shell electrons.

Electron(ic) structure or configuration

The arrangement of electrons in an atom.

Electronegativity

A measure of the attraction of a bonded atom for the pair of electrons in a covalentbond.

Electrophile

An atom (or group of atoms) which is attracted to an electron-rich centre or atom,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-richcentre or atom, where it accepts a pair of electrons to form a new covalent bond.

Elimination reactionThe removal of a molecule from a saturated molecule to make an unsaturated

7/30/2019 Chemistry Glossary for A2

7/21

molecule.

Empirical formula

The simplest whole-number ratio of atoms of each element present in a compound.

Enantiomers

Stereoisomers that are non-superimposable mirror images of each other; also calledoptical isomers.

End point

The point in a titration at which there are equal concentrations of the weak acid andconjugate base forms of the indicator. The colour at the end point is midway betweenthe colours of the acid and conjugate base forms.

Endothermic

A reaction in which the enthalpy of the products is greater than the enthalpy of thereactants, resulting in heat being taken in from the surroundings (H+ve).

(Standard) enthalpy change of atomisation

The enthalpy change that takes place when one mole of gaseous atoms forms fromthe element in its standard state.

(Standard) enthalpy change of combustion,

The enthalpy change that takes place when one mole of a substance reactscompletely with oxygen under standard conditions, all reactants and products beingin their standard states.

(Standard) enthalpy change of formation,

The enthalpy change that takes place when one mole of a compound is formed fromits 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 isdissolved in water, forming one mole of aqueous ions, under standard conditions.

(Standard) enthalpy change of neutralisation,

The energy change that accompanies the neutralisation of an aqueous acid by an

7/30/2019 Chemistry Glossary for A2

8/21

aqueous base to form one mole of H2O(l), under standard conditions.

(Standard) enthalpy change of reaction,

The enthalpy change that accompanies a reaction in the molar quantities expressedin a chemical equation under standard conditions, all reactants and products being intheir standard states.

(Standard) enthalpy change of solution

The enthalpy change that takes place when one mole of a compound is completelydissolved in water under standard conditions.

Enthalpy cycle

A diagram showing alternative routes between reactants and products that allowsthe indirect determination of an enthalpy change from other known enthalpy changesusing Hesss law.

Enthalpy profile diagram

A diagram for a reaction to compares the enthalpy of the reactants with the enthalpyof the products.

Enthalpy, HThe heat content that is stored in a chemical system.

Entropy, S

The quantitative measure of the degree of disorder in a system.

(Standard) entropy change of reaction,

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

Equilibrium law

7/30/2019 Chemistry Glossary for A2

9/21

Equivalence point

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

the volume of the second solution. This matches the stoichiometry of the reactionthat is taking place.

Esterification

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

Exothermic

A reaction in which the enthalpy of the products is smaller than the enthalpy of thereactants, resulting in heat loss to the surroundings (Hve).

Fragmentation

The process in mass spectrometry that causes a positive ion to spilt into pieces, oneof which is a positive fragment ion.

Free energy change,G

The balance between enthalpy, entropy and temperature for a process:G=HTS. A process can take place spontaneously whenG< 0.

Functional group

The part of the organic molecule responsible for its chemical reactions.

General formula

The simplest algebraic formula of a member of a homologous series. For example,the general formula of the alkanes is CnH2n+2.

Giant covalent lattice

A three-dimensional structure of atoms, bonded together by strong covalent bonds.

Giant ionic lattice

A three-dimensional structure of oppositely charged ions, bonded together by strongionic bonds.

Giant metallic lattice

A three-dimensional structure of positive ions and delocalised electrons, bondedtogether by strong metallic bonds.

Greenhouse effect

7/30/2019 Chemistry Glossary for A2

10/21

The process in which the absorption and subsequent emission of infrared radiationby atmospheric gases warms the lower atmosphere and the planets surface.

Group

A vertical column in the Periodic Table. Elements in a group have similar chemicalproperties and their atoms have the same number of outer-shell electrons.

Half-life

The time taken for the concentration of a reactant to reduce by half.

Hesss Law

If a reaction can take place by more than one route and the initial and final conditionsare the same, the total enthalpy change is the same for each route.

Heterogeneous catalysis

A reaction in which the catalyst has a different physical state from the reactants;frequently reactants are gases whilst the catalyst is a solid.

Heterogeneous equilibrium

An equilibrium in which the species making up the reactants and products are indifferent physical states.

Heterolytic fission

The breaking of a covalent bond with both of the bonded electrons going to eachatom, forming a cation (+ ion) and an anion ( ion).

High-density lipoprotein (HDL)

A type of lipoprotein that can remove cholesterol from the arteries and transport itback to the liver for excretion or re-utilisation.

Homogeneous catalysis

A reaction in which the catalyst and reactants are in the same physical state, whichis most frequently the aqueous or gaseous state.

Homogeneous equilibrium

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

Homologous seriesA series of organic compounds with the same functional group but with each

7/30/2019 Chemistry Glossary for A2

11/21

successive member differing by CH2.

Homolytic fission

The breaking of a covalent bond with one of the bonded electrons going to eachatom, forming two radicals.

Hydrated

A crystalline compound containing water molecules.

Hydrocarbon

A compound of hydrogen and carbon only.

Hydrogen bond

A strong dipoledipole attraction between an electron-deficient hydrogen atom (OH+, NH+ or FH+) on one molecule and a lone pair of electrons on a highlyelectronegative atom (HO:, HN: HF:) on a different molecule.

Hydrolysis

A reaction with water that breaks a chemical compound into two compounds; the Hand OH in a watermolecule becomes incorporated into the two compounds.Initial rate of reaction

The change in concentration of a reactant or product per unit time at the start of thereaction: t= 0.

Initiation

The first step in a radical substitution in which the free radicals are generated byultraviolet radiation.

Intermediate

A species formed in one step and used up in a subsequent step and so never seenas either a reactant or a product.

Intermolecular force

An attractive force between neighbouring molecules. Intermolecular forces can bevan der Waals forces, dipoledipole forces or hydrogen bonding.

Ion

7/30/2019 Chemistry Glossary for A2

12/21

A positively or negatively charged atom or a (covalently bonded) group of atoms (amolecular ion).

Ionic bondingThe electrostatic attraction between oppositely charged ions.

Ionic product of water, Kw

Kw = [H+(aq)] [OH(aq)]

At 25C, Kw = 1.00 1014 mol2dm6.

(First) ionisation energy

The energy required to remove one electron from each atom in one mole of gaseousatoms to form one mole of gaseous 1+ ions.

(Second) ionisation energy

The energy required to remove one electron from each ion in one mole of gaseous1+ ions to form one mole of gaseous 2+ ions.

Isoelectric point

The point at which an amino acid has no overall charge.

Isotopes

Atoms of the same element with different numbers of neutrons and different masses.

Lattice enthalpy

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

Le Chateliers Principle

When a system in dynamic equilibrium is subjected to a change, the systemreadjusts itself to minimise the effect of the change and to restore equilibrium.

Ligand

A molecule or ion that can donate a pair of electrons to a transition metal ion.

Ligand substitution

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

7/30/2019 Chemistry Glossary for A2

13/21

Limiting reagent

The substance in a chemical reaction that runs out first.

Lone pair

An outer-shell pair of electrons that is not involved in chemical bonding.

Low-density lipoprotein (LDL)

A type of lipoprotein responsible for carrying cholesterol and triglycerides from theliver to the tissues.

Mass (nucleon) numberThe number of particles, protons and neutrons, in the nucleus.

Mechanism

A sequence of steps, showing the path taken by electrons in a reaction.

Metallic bond

The electrostatic attraction between positive metal ions and delocalised electrons.

Mobile phase

The phase that moves in chromatography.

Molar mass, M

The mass per mole of a substance. The units of molar mass are

gmol1.

MoleThe amount of any substance containing as many elementary particles as there are

carbon atoms in exactly 12g of the carbon-12 isotope.

Molecular formula

The actual number of atoms of each element in a molecule.

Molecular ion, M+

The positive ion formed in mass spectrometry when a molecule loses an electron.

7/30/2019 Chemistry Glossary for A2

14/21

Molecule

A small group of atoms held together by covalent bonds.

Monomer

A small molecule that combines with many other monomers to form a polymer.

Neutralisation

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

Nomenclature

A system of naming compounds.

Nucleophile

An atom (or group of atoms) which is attracted to an electron-deficient centre oratom, where it donates a pair of electrons to form a new covalent bond.

Optical isomers

Stereoisomers that are non-superimposable mirror images of each other; also calledenantiomers.

Order

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

Overall order

The sum of the individual orders: m+ n.

Oxidation

Loss of electrons or an increase in oxidation number.

Oxidation number

A measure of the number of electrons that an atom uses to bond with atoms ofanother element. Oxidation numbers are derived from a set of rules.

Oxidising agent

A reagent that oxidises (takes electrons from) another species.

Peptide

A compound containing amino acids linked by peptide bonds. Often the number ofamino acids is indicated by the prefix, di-, tri-, tetra-:

7/30/2019 Chemistry Glossary for A2

15/21

dipeptide = 2 amino acids

tripeptide = 3 amino acids

tetrapeptide = 4 amino acids.

Percentage yield

Period

A horizontal row of elements in the Periodic Table. Elements show trends inproperties across a period.

Periodicity

A regular periodic variation of properties of elements with atomic number andposition in the Periodic Table.

Permanent dipole

A small charge difference across a bond resulting from a difference inelectronegativities of the bonded atoms.

pH

pH =log[H+(aq)][H+(aq)] = 10pH.

Pharmacological activity

The beneficial or adverse effects of a drug on living matter.

Phase

A physically distinctive form of a substance, such as the solid, liquid and gaseous

states of ordinary matter.

pi-bond

The reactive part of a double bond formed above and below the plane of the bondedatoms by sideways overlap of p-orbitals.

Polar covalent bond

A bond with a permanent dipole.

Polar molecule

7/30/2019 Chemistry Glossary for A2

16/21

A molecule with an overall dipole, having taken into account any dipoles acrossbonds.

PolymerA long molecular chain built up from monomer units.

Precipitation reaction

The formation of a solid from a solution during a chemical reaction. Precipitates areoften formed when two aqueous solutions are mixed together.

Principal quantum number, n

A number representing the relative overall energy of each orbital, which increases withdistance from the nucleus. The sets of orbitals with the same n-value are referred toas electron shells or energy levels.

Propagation

The two repeated steps in radical substitution which build up the products in a chainreaction.

Radical

A species with an unpaired electron.

Rate constant, k

The constant that links the rate of reaction with the concentrations of the reactantsraised to the powers of their orders in the rate equation.

Rate equation

For a reaction: A + BC, the rate equation is given by:

rate= k[A]m[B]n.

mis the order of reaction with respect to A.

nis the order of reaction with respect to B.

m+ n= overall order.

Rate of reaction

The change in concentration of a reactant or a product in a given time.

Rate-determining step

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

7/30/2019 Chemistry Glossary for A2

17/21

Reaction mechanism

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

Redox reaction

A reaction in which both reduction and oxidation take place.

Reducing agent

A reagent that reduces (adds electrons to) another species.

Reduction

Gain of electrons or a decrease in oxidation number.

Reflux

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

Relative atomic mass, Ar

The weighted mean mass of an atom of an element compared with one-twelfth of themass of an atom of carbon-12.

Relative formula mass

The weighted mean mass of the formula unit of a compound compared with one-twelfth of the mass of an atom of carbon-12.

Relative isotopic mass

The mass of an atom of an isotope compared with one-twelfth of the mass of anatom of carbon-12.

Relative molecular mass, Mr

The weighted mean mass of a molecule of a compound compared with one-twelfthof the mass of an atom of carbon-12.

Repeat unit

A specific arrangement of atoms that occurs in the structure over and over again.Repeat units are included in brackets, outside which is the symbol n.

7/30/2019 Chemistry Glossary for A2

18/21

Retention time

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

Rf value

Salt

A chemical compound formed from an acid, when an H+ ion from the acid has beenreplaced by a metal ion or another positive ion, such as the ammonium ion, NH4+.

Saturated hydrocarbon

A hydrocarbon with single bonds only.

Shell

A group of atomic orbitals with the same principal quantum number, n. Also knownas a main energy level.

Simple molecular latticeA three-dimensional structure of molecules, bonded together by weak intermolecularforces.

Skeletal formula

A simplified organic formula, with hydrogen atoms removed from alkyl chains,leaving just a carbon skeleton and associated functional groups.

Specific heat capacity, c

The energy required to raise the temperature of 1g of a substance by 1 C.

Spectator ions

Ions that are present but play no part in a chemical reaction

Spinspin coupling

The interaction between spin states of non-equivalent nuclei that results in a group ofpeaks in an NMR spectrum.

7/30/2019 Chemistry Glossary for A2

19/21

Stability constant, Kstab

The equilibrium constant for an equilibrium existing between a transition metal ionsurrounded by water ligands and the complex formed when the same ion hasundergone a ligand substitution reaction.

Standard conditions

A pressure of 100kPa (1atmosphere), a stated temperature, usually 298K (25C)and a concentration of 1 mol dm3 (for reactions with aqueous solutions).

Standard electrode potential,

The e.m.f. of a half cell compared with a standard hydrogen half cell, measured at

298K with solution concentrations of 1 moldm3 and a gas pressure of 101 kPa (1atmosphere).

Stationary phase

The phase that does not move in chromatography.

Stem

The longest carbon chain present in an organic molecule.

Stereoisomers

Compounds with the same structural formula but with a different arrangement of theatoms in space.

Stoichiometry

The molar relationship between the relative quantities of substances taking part in areaction.

StratosphereThe second layer of the Earths atmosphere, containing the ozone layer, between

about 10km and 50km above the Earths surface.

Strong acid

An acid that completely dissociates in solution.

Structural formula

A formula showing the minimal detail for the arrangement of atoms in a molecule.

7/30/2019 Chemistry Glossary for A2

20/21

Structural isomers

Molecules with the same molecular formula but with different structuralarrangements of atoms.

Sub-shell

A group of the same type of atomic orbitals (s, p, d or f) within a shell.

Substitution reaction

A reaction in which an atom or group of atoms is replaced with a different atom orgroup of atoms.

SuffixThe part of the name added afterthe stem.

Termination

The step at the end of a radical substitution when two radicals combine to form amolecule.

Thermal decomposition

The breaking up of a chemical substance with heat into at least two chemicalsubstances.

Transition element

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

Troposphere

The lowest layer of the Earths atmosphere, extending from the Earths surface up to

about 7km (above the poles) to about 20 km (above the tropics).

Unsaturated hydrocarbon

A hydrocarbon containing multiple carbon-to-carbon bonds.

Valence shell

The outermost shell of an atom, which contains the electrons most likely to react andbond to other atoms.

van der Waals forceAn attractive force between instantaneous dipoles and induced dipoles in

7/30/2019 Chemistry Glossary for A2

21/21

neighbouring molecules.

Volatility

The ease with which a liquid turns into a gas. Volatility increases as boiling point

decreases.Water of crystallisation

Water molecules that form an essential part of the crystalline structure of acompound.

Weak acid

An acid that partially dissociates in solution.

ZwitterionA dipolar ionic form of an amino acid that is formed by the donation of a hydrogenion from the carboxyl group to the amino group. As both charges are present there isno overall charge.