Chemistry A2

Front 1

Acid-base pair

Back 1

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

Front 2

Activation energy

Back 2

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

Front 3

Addition Polymer

Back 3

A very long molecular chain, formed by repeated addition reactions of many unsaturated alkene molecules.

Front 4

Addition Reaction

Back 4

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

Front 5

Adsorbtion

Back 5

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

Front 6

Alicyclic hydrocarbon

Back 6

A hydrocarbon with carbon joining together in a ring structure.

Front 7

Aliphatic hydrocarbon

Back 7

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

Front 8

Alkali

Back 8

A type of base that dissolves in water to form hydroxide ions, OH⁻ ions.

Front 9

Alkanes

Back 9

The homologous with the general formula

CnH2n+2

Front 10

Alkyl group

Back 10

An alkane with a hydrogen atom removed.

Front 11

Amount of substance

Back 11

The quantity whose unit is the mole. Chemistry use "amount of substance" as a means of counting atoms.

Front 12

Anhydrous

Back 12

A substance that contains no water.

Front 13

Anoin

Back 13

A negatively charged ion.

Front 14

Average bond enthalpy

Back 14

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

Front 15

Avogadro's constant

Back 15

The number of atoms per mole of the carbon-12 isotope. (6.02x10²³mol⁻¹)

Front 16

Biodegradable substance

Back 16

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

Front 17

Biodegradable polymer

Back 17

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

Front 18

Boltzmann distribution

Back 18

A diagram showing the distribution of energies of the molecules at a particular temperature.

Front 19

Bond dissociation enthalpy

Back 19

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

Front 20

Brønsted–Lowry acid

Back 20

A species that is a proton donor.

Front 21

Brønsted–Lowry base

Back 21

A species that is a proton acceptor.

Front 22

Buffer solution

Back 22

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

Front 23

Carbanion

Back 23

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

Front 24

Carbocation

Back 24

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

Front 25

Catalyst

Back 25

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

Front 26

Cation

Back 26

A positively charged ion.

Front 27

Chemical shift

Back 27

A scale that compares the frequency of a NMR absorption with the frequency of the reference peak of TMS at δ=0ppm.

Front 28

Chiral carbon

Back 28

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

Front 29

Chromatogram

Back 29

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

Front 30

cis-trans isomerism

Back 30

A special type of E/Z isomerism in which each carbon of the C=C double bond carries the same atom or group on each side: cis isomerism is the same both sides, trans is different on each side.

Front 31

Complex ion

Back 31

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

Front 32

Condensation Reaction

Back 32

A reaction in which two small molecules react together to form one larger molecule with the elimination of a small molecule such as water.

Front 33

Conjugate Acid

Back 33

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

Front 34

Conjugate base

Back 34

A species formed when a proton is removed from an acid.

Front 35

Coordinate Bond

Back 35

A shared pair of electrons in which the bonded pair has been provided by one bonding atom only, also called a dative covalent bond.

Front 36

Coordinate number

Back 36

The total number of coordinate bonds formed between the central metal and any ligands.

Front 37

Cracking

Back 37

The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter chained alkanes and alkenes.

Front 38

Curly Arrow

Back 38

A symbol used in a reaction to show the movement of a pair of electrons, during the breaking or formation of a covalent bond.

Front 39

Degradable polymer

Back 39

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

Front 40

Dehydration

Back 40

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

Front 41

Delocalised electrons

Back 41

Electrons that are shared between more that two atoms.

Front 42

Dipole-Dipole Force

Back 42

An attractive force between permanent dipoles in neighbouring polar molecules.

Front 43

Displacment reaction

Back 43

A reaction in which a more reactive element displaces a less reactive molecule and the bonds between them.

Front 44

Displayed formula

Back 44

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

Front 45

Disproportionation

Back 45

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

Front 46

Dynamic equilibrium

Back 46

The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction.

Front 47

E/Z Isomerism

Back 47

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

Front 48

(First) electron affinity

Back 48

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

Front 49

Electron Shielding

Back 49

The repulsion between electrons in different inner shells. Sheilding reduces the net attractive force from the positive nucleus to an outershell negative electron.

Front 50

Electronic Structure

Back 50

The arrangement of electrons in an atom.

Front 51

Electronegativety

Back 51

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

Front 52

Electrophile

Back 52

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

Front 53

Electrophilic substitution

Back 53

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.

Front 54

Elimination reaction

Back 54

The removal of a molecule from a saturated molecule to make an unsaturated molecule.

Front 55

Empirical formula

Back 55

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

Front 56

Enantiomers

Back 56

Stereoisomers that are non-superimposable mirror images of each other, also called optical isomers.

Front 57

Endpoint

Back 57

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

Front 58

Endothermic

Back 58

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

Front 59

(Standard) enthalpy change of atomisation

Back 59

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

Front 60

(Standard) enthalpy change of combustion

Back 60

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

Front 61

(Standard) enthalpy change of formation

Back 61

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.

Front 62

(Standard) enthalpy change of hydration

Back 62

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.

Front 63

(Standard) enthalpy change of reaction

Back 63

The enthalpy 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.

Front 64

(Standard) enthalpy change of solution

Back 64

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

Front 65

Enthalpy cycle

Back 65

A diagram showing alternative routes between reactants and products that allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess’s law.

Front 66

Enthalpy profile diagram

Back 66

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

Front 67

Enthalpy, H

Back 67

The heat content that is stored in a chemical system.

Front 68

Entropy, S

Back 68

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

Front 69

Equilibrium law

Back 69

Front 70

Equivalence point

Back 70

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 reaction that is taking place.

Front 71

Esterification

Back 71

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

Front 72

Exothermic

Back 72

A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (ΔH –ve).

Front 73

Fragmentation

Back 73

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

Front 74

Free energy change, ΔG

Back 74

The balance between enthalpy, entropy and temperature for a process: ΔG = ΔH – TΔS. A process can take place spontaneously when ΔG < 0.

Front 75

Functional group

Back 75

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

Front 76

General formula

Back 76

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

Front 77

Giant covalent lattice

Back 77

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

Front 78

Giant ionic lattice

Back 78

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

Front 79

Giant metallic lattice

Back 79

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

Front 80

Greenhouse effect

Back 80

The process in which the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and the planet’s surface.

Front 81

Group

Back 81

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

Front 82

Half-life

Back 82

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

Front 83

Hess's Law

Back 83

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

Front 84

Heterogeneous catalysis

Back 84

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

Front 85

Heterogeneous equilibrium

Back 85

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

Front 86

Heterolytic fission

Back 86

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

Front 87

High-density lipoprotein (HDL)

Back 87

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

Front 88

Homogeneous catalysis

Back 88

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

Front 89

Homogeneous equilibrium

Back 89

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

Front 90

Homologous series

Back 90

A series of organic compounds with the same functional group but with each successive member differing by CH2.

Front 91

Homolytic fission

Back 91

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

Front 92

Hydrated

Back 92

A crystalline compound containing water molecules.

Front 93

Hydrocarbon

Back 93

A compound of hydrogen and carbon only.

Front 94

Hydrogen Bond

Back 94

A strong dipole–dipole attraction between an electron-deficient hydrogen atom (O–Hδ+, N–Hδ+ or F–Hδ+) on one molecule and a lone pair of electrons on a highly electronegative atom (HδO:δ–, HδN:δ– HδF:δ–) on a different molecule.

Front 95

Hydrolysis

Back 95

A reaction with water that breaks a chemical compound into two compounds; the H and OH in a water molecule becomes incorporated into the two compounds.

Front 96

Initial rate of reaction

Back 96

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

Front 97

Initiation

Back 97

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

Front 98

Intermediate

Back 98

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

Front 99

Intermolecular force

Back 99

An attractive force between neighbouring molecules. Intermolecular forces can be van der Waals’ forces, dipole–dipole forces or hydrogen bonding.

Front 100

Ion

Back 100

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

Front 101

Ionic bonding

Back 101

The electrostatic attraction between oppositely charged ions.

Front 102

Ionic product of water, Kw

Back 102

Kw = [H+(aq)] [OH–(aq)] At 25 °C, Kw = 1.00 × 10–14 mol2 dm–6.

Front 103

(First) ionisation energy

Back 103

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

Front 104

(Second) ionisation energy

Back 104

The energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

Front 105

Isoelectric Point

Back 105

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

Front 106

Isotopes

Back 106

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

Front 107

Lattice enthalpy

Back 107

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

Front 108

Le Chatelier’s Principle

Back 108

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

Front 109

Ligand

Back 109

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

Front 110

Ligand substitution

Back 110

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

Front 111

Limiting reagent

Back 111

The substance in a chemical reaction that runs out first.

Front 112

Lone pair

Back 112

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

Front 113

Low-density lipoprotein (LDL)

Back 113

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

Front 114

Mass (nucleon) number

Back 114

The number of particles, protons and neutrons, in the nucleus.

Front 115

Mechanism

Back 115

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

Front 116

Metallic bond

Back 116

The electrostatic attraction between positive metal ions and delocalised electrons.

Front 117

Mobile phase

Back 117

The phase that moves in chromatography.

Front 118

Molar mass, M

Back 118

The mass per mole of a substance. The units of molar mass are g mol–1.

Front 119

Mole

Back 119

The amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12 g of the carbon-12 isotope.

Front 120

Molecular formula

Back 120

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

Front 121

Molecular ion, M+

Back 121

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

Front 122

Molecule

Back 122

A small group of atoms held together by covalent bonds.

Front 123

Monomer

Back 123

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

Front 124

Neutralisation

Back 124

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

Front 125

Nomenclature

Back 125

A system of naming compounds.

Front 126

Nucleophile

Back 126

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

Front 127

Order

Back 127

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

Front 128

Overall order

Back 128

The sum of the individual orders: m + n.

Front 129

Oxidation

Back 129

Loss of electrons or an increase in oxidation number.

Front 130

Oxidation number

Back 130

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

Front 131

Oxidising agent

Back 131

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

Front 132

Peptide

Back 132

A compound containing amino acids linked by peptide bonds. Often the number of amino acids is indicated by the prefix, di-, tri-, tetra-:
dipeptide = 2 amino acids
tripeptide = 3 amino acids
tetrapeptide = 4 amino acids.

Front 133

Percentage yeild

Back 133

(actual amount / theoretical amount) x 100

Front 134

Period

Back 134

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

Front 135

Periodicity

Back 135

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

Front 136

Permanent dipole

Back 136

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

Front 137

pH

Back 137

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

Front 138

Pharmacological activity

Back 138

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

Front 139

Phase

Back 139

A physically distinctive form of a substance, such as the solid, liquid and gaseous states of ordinary matter.

Front 140

pi-bond

Back 140

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

Front 141

Polar covalent bond

Back 141

A bond with a permanent dipole.

Front 142

Polar molecule

Back 142

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

Front 143

Polymer

Back 143

A long molecular chain built up from monomer units.

Front 144

Precipitation reaction

Back 144

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

Front 145

Principal quantum number, n

Back 145

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

Front 146

Propagation

Back 146

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

Front 147

Radical

Back 147

A species with an unpaired electron.

Front 148

Rate constant, k

Back 148

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.

Front 149

Rate equation

Back 149

For a reaction: A + B → C, the rate equation is given by:
rate = k[A]m[B]n.
m is the order of reaction with respect to A.
n is the order of reaction with respect to B.
m + n = overall order.

Front 150

Rate of Reaction

Back 150

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

Front 151

Rate-determining step

Back 151

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

Front 152

Reaction mechanism

Back 152

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

Front 153

Redox reaction

Back 153

A reaction in which both reduction and oxidation take place.

Front 154

Reducing agent

Back 154

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

Front 155

Reduction

Back 155

Gain of electrons or a decrease in oxidation number.

Front 156

Reflux

Back 156

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

Front 157

Relative atomic mass, Ar

Back 157

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

Front 158

Relative formula mass

Back 158

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

Front 159

Relative isotopic mass

Back 159

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

Front 160

Relative molecular mass, Mr

Back 160

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

Front 161

Repeat unit

Back 161

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.

Front 162

Retention time

Back 162

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

Front 163

Rf value

Back 163

Front 164

Salt

Back 164

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

Front 165

Saturated hydrocarbon

Back 165

A hydrocarbon with single bonds only.

Front 166

Shell

Back 166

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

Front 167

Simple molecular lattice

Back 167

A three-dimensional structure of molecules, bonded together by weak intermolecular forces.

Front 168

Skeletal formula

Back 168

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

Front 169

Specific heat capacity, c

Back 169

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

Front 170

Spectator ions

Back 170

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

Front 171

Spin–spin coupling

Back 171

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

Front 172

Stability constant, K stab

Back 172

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

Front 173

Standard conditions

Back 173

A pressure of 100 kPa (1 atmosphere), a stated temperature, usually 298 K (25 °C) and a concentration of 1 mol dm–3 (for reactions with aqueous solutions).

Front 174

Standard electrode potential,

Back 174

The e.m.f. of a half cell compared with a standard hydrogen half cell, measured at 298 K with solution concentrations of 1 mol dm–3 and a gas pressure of 101 kPa (1 atmosphere).

Front 175

Stationary phase

Back 175

The phase that does not move in chromatography.

Front 176

Stem

Back 176

The longest carbon chain present in an organic molecule.

Front 177

Stereoisomers

Back 177

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

Front 178

Stoichiometry

Back 178

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

Front 179

Stratosphere

Back 179

The second layer of the Earth’s atmosphere, containing the ‘ozone layer’, between about 10 km and 50 km above the Earth’s surface.

Front 180

Strong acid

Back 180

An acid that completely dissociates in solution.

Front 181

Structural formula

Back 181

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

Front 182

Structural isomers

Back 182

Molecules with the same molecular formula but with different structural arrangements of atoms.

Front 183

Sub-shell

Back 183

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

Front 184

Substitution reaction

Back 184

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

Front 185

Suffix

Back 185

The part of the name added after the stem.

Front 186

Termination

Back 186

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

Front 187

Thermal decomposition

Back 187

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

Front 188

Transition element

Back 188

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

Front 189

Troposphere

Back 189

The lowest layer of the Earth’s atmosphere, extending from the Earth’s surface up to about 7 km (above the poles) to about 20 km (above the tropics).

Front 190

Unsaturated hydrocarbon

Back 190

A hydrocarbon containing multiple carbon-to-carbon bonds.

Front 191

Valence shell

Back 191

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

Front 192

van der Waals’ force

Back 192

An attractive force between instantaneous dipoles and induced dipoles in neighbouring molecules.

Front 193

Volatility

Back 193

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

Front 194

Water of crystillisation

Back 194

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

Front 195

Weak acid

Back 195

An acid that partially dissociates in solution.

Front 196

Zwitterion

Back 196

A dipolar ionic form of an amino acid that is formed by the donation of a hydrogen ion from the carboxyl group to the amino group. As both charges are present there is no overall charge.