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A-level chemistry > Key Definitions > Flashcards

Key Definitions Flashcards

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1
Q

Acid

A

A proton donor

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2
Q

Activation energy

A

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

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3
Q

Addition polymer

A

A very long molecular chain, formed by repeated additional reactions of many unsaturated alkene molecules (monomers).

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4
Q

Addition polymerisation

A

The process in which unsaturated alkene molecules (monomers) add on to a growing polymer chain one at a time to form a very long saturated molecular chain (the addition polymer).

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5
Q

Addition reaction

A

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

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6
Q

Absorbtion

A

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

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7
Q

Alicyclic hydrocarbon

A

A hydrocarbon with carbon atoms joined together in a ring like structure

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8
Q

Aliphatic hydrocarbon

A

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

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9
Q

Alkali

A

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

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10
Q

Alkanes

A

The homologous series with the general formula: CnH2n+2

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11
Q

Alkyl group

A

An alkane with a hydrogen atom removed, e.g. CH3, C2H5

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12
Q

Amount of substance

A

The quantity whose unit is the mole. Chemists use ‘amount of substance’ as a means of counting atoms.

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13
Q

Anhydrous

A

A substance containing no water molecules

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14
Q

Anion

A

A negatively charged ion

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15
Q

Atom economy

A

molecular mass of the desired product
= ————————————————————- X100
sum of molecular masses of all products

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16
Q

Atomic orbital

A

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

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17
Q

Atomic (proton) number

A

The number of protons in the nucleus of an atom

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18
Q

Average bond enthalpy

A

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

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19
Q

Avogadro constant, Na

A

The number of atoms per mole of the carbon-12 isotope (6.02 x 10(23) mol -1

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20
Q

Base

A

A proton acceptor

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21
Q

Biodegradable material

A

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

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22
Q

Boltzmann distribution

A

The distribution of energies of molecules at a particular temperature, usually shown as a graph

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23
Q

Bond enthalpy

A

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

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24
Q

Carbanion

A

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

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25
Q

Carbocation

A

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

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26
Q

Catalyst

A

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

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27
Q

Cation

A

A positively charged ion

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28
Q

cis-trans isomerism

A

A special type of E/Z isomerism in which there is a non-hydrogen group and hydrogen on each C of a C=C double bond: the cis isomer (Z isomer) has the H atoms on each carbon on the same side; the trans isomer (E isomer) has the H atoms on each carbon on different sides.

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29
Q

Compound

A

A substance formed from two or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula

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30
Q

Concentration

A

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

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31
Q

Coordinate bond

A

A shared pair of electrons which has been provided by one of the bonding atoms only; also called a dative covalent bond

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32
Q

Covalent bond

A

A bond formed by a shared pair of electrons

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33
Q

Cracking

A

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

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34
Q

Curly arrow

A

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

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35
Q

Dative covalent bond

A

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

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36
Q

Dehydration

A

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

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37
Q

Delocalised electrons

A

Electrons that are shared between more than two atoms

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38
Q

Displacement reaction

A

A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of the latter’s ions

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39
Q

Displayed formula

A

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

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40
Q

Disproportionation

A

The oxidation and reduction of the same element in a redox reaction

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41
Q

Dynamic equilibrium

A

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

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42
Q

E/Z isomerism

A

A type of stereo-isomerism in which different groups attached to each carbon of a C=C double bond may be arranged different in space because of the restricted rotation of the C=C bond

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43
Q

Electron configuration

A

The arrangement of electrons in an atom

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44
Q

Electronegativity

A

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

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45
Q

Electron sheilding

A

The repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus of the outer-shell electrons

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46
Q

Electrophile

A

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

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47
Q

Electrophilic addition

A

A type of addition 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

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48
Q

Elimination reaction

A

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

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49
Q

Empirical formula

A

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

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50
Q

Endothermic reaction

A

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

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51
Q

Enthalpy, H

A

The hear content that is stored in a chemical system

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52
Q

Standard enthalpy change of combustion

A

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

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53
Q

Standard enthalpy change of formation

A

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

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54
Q

Standard enthalpy change of reaction

A

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

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55
Q

Enthalpy cycle

A

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’ law.

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56
Q

Enthalpy profile diagram

A

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

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57
Q

Esterification

A

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

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58
Q

Exothermic reaction

A

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

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59
Q

Fractional distillation

A

The separation of the components in a liquid mixture into fraction which differ in boiling point (and hence chemical composition) by means of distillation, typically using a fractionating column.

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60
Q

Fragmentation

A

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

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61
Q

Functional group

A

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

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62
Q

General formula

A

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

63
Q

Giant covalent lattice

A

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

64
Q

Giant ionic lattice

A

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

65
Q

Giant metallic lattice

A

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

66
Q

Greenhouse effect

A

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

67
Q

Group

A

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

68
Q

Hess’ law

A

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

69
Q

Heterogeneous catalysis

A

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

70
Q

Heterolytic fission

A

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

71
Q

Homogeneous catalysis

A

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

72
Q

Homologous series

A

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

73
Q

Homolytic fission

A

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

74
Q

Hydrated

A

Crystalline and containing water molecules

75
Q

Hydrocarbon

A

An organic compound of hydrogen and carbon only

76
Q

Hydrogen bond

A

A strong dipole-dipole attraction between an electron-deficiant hydrogen atom (O-H[sightly]+ or N-H[slightly]+) on one molecule and a lone pair of electrons on a highly electronegative atom (H-O:[slightly]- or H-N:[slightly]- ) on a different molecule.

77
Q

Hydrolysis

A

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

78
Q

Initiation

A

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

79
Q

Intermolecular force

A

An attractive force between neighbouring molecules. Intermolecular forces can be van der Waals’ forces (induced dipole-dipole forces), permanent dipole-dipole forces or hydrogen bonds.

80
Q

Ion

A

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

81
Q

Ionic bond

A

The electrostatic attraction between oppositely charged ions.

82
Q

(first) ionisation energy

A

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

83
Q

(second) ionisation energy

A

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

84
Q

(successive) ionisation energy

A

A measure of the energy required to remove each electron in turn, e.g. the second ionisation energy is 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

85
Q

Isotopes

A

Atoms of the same element with different number of neutrons and different masses

86
Q

le Chatelier’s principle

A

When a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change

87
Q

Limiting reagent

A

The substance in a chemical reaction the runs out first

88
Q

Lone pair

A

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

89
Q

Mass (nucleon) number

A

The number of particles (protons and neutrons) in the nucleus

90
Q

Mechanism

A

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

91
Q

Metallic bond

A

The electrostatic attraction between positive metal ions and delocalised electrons

92
Q

Molar mass, M

A

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

93
Q

Molar volume

A

The volume per mole of a gas. The units of molar volume are dm3 mol-1. At room temperature and pressure the molar volume is approximately 24.0 dm3mol-1

94
Q

Mole

A

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

95
Q

Molecular formula

A

The number of atoms of each element in a molecule

96
Q

Molecular ion, M+

A

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

97
Q

Molecule

A

A small group of atoms help together by covalent bonds

98
Q

Monomer

A

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

99
Q

Nomenclature

A

A system of naming compounds

100
Q

Nucleophile

A

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

101
Q

Nucleophilic substitution

A

A type of substitution reaction in which a nucleophile is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond

102
Q

Oxidation

A

Loss of electrons or an increase in oxidation number

103
Q

Oxidation number

A

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

104
Q

Oxidising agent

A

A reagent that oxidises (takes electrons from) another species

105
Q

Percentage yield

A

actual amount, in mol, of product
= ———————————————————— x100
Theoretical amount, in mol, of product

106
Q

Period

A

A horizontal row of elements in the periodic table. Elements show trends in properties across a period

107
Q

Periodicity

A

A regular periodic variation of properties of elements with atomic number and position in the periodic table

108
Q

Permanent dipole

A

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

109
Q

Permanent dipole-dipole force

A

An attractive force between permanent dipoles in neighbouring polar molecules

110
Q

pi-bond

A

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

111
Q

Polar covalent bond

A

A bond with a permanent dipole

112
Q

Polar molecule

A

A molecule with an overall dipole, taking into account any dipoles across bonds

113
Q

Polymer

A

A long molecular chain built up from monomer units

114
Q

Precipitation reaction

A

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

115
Q

Principal quantum number, n

A

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

116
Q

Propagation

A

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

117
Q

Radical

A

A species with an unpaired electron

118
Q

Radical substitution

A

A type of substitution reaction in which a radical replaces a different atom or group of atoms

119
Q

Rate of reaction

A

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

120
Q

Redox reaction

A

A reaction in which both reduction and oxidation take place

121
Q

Reducing agent

A

A reagent that reduces (add electrons to) another species

122
Q

Reduction

A

Gain of electrons of a decrease in oxidation number

123
Q

Reflux

A

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

124
Q

Relative atomic mass, Ar

A

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

125
Q

Relative formula mass

A

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

126
Q

Relative isotopic mass

A

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

127
Q

Relative molecular mass, Mr

A

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

128
Q

Repeat unit

A

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

129
Q

Salt

A

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

130
Q

Saturated hydrocarbon

A

A hydrocarbon with single bonds only and have the maximum number of hydrogen atoms bonded to it. CnH2n+2

131
Q

Shell

A

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

132
Q

Simple molecular lattice

A

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

133
Q

Skeletal formula

A

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

134
Q

Species

A

Any type of particle that takes part in a chemical reaction

135
Q

Specific heat capacity

A

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

136
Q

Spectator ions

A

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

137
Q

Standard conditions

A

A pressure of 100kPa (1 atomsphere), a stated temperature, usually 298 K (25 degrees C), and a concentration of 1 mol dm-3 (for reaction with aqueous solutions).

138
Q

Standard solution

A

A solution of known concentration. Standard solutions are normally used in titrations to determine unknown information about another substance.

139
Q

Standard state

A

The physical state of a substance under the standard conditions of 100kPa (1 atmosphere) and 298 K (25 degrees C).

140
Q

Stereoisomers

A

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

141
Q

Stoichiometry

A

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

142
Q

Stratosphere

A

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

143
Q

Structural formula

A

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

144
Q

Structural isomers

A

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

145
Q

Sub-shell

A

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

146
Q

Substitution reaction

A

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

147
Q

Termination

A

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

148
Q

Thermal decomposition

A

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

149
Q

Troposphere

A

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

150
Q

Unsaturated hydrocarbon

A

A hydrocarbon containing carbon-to-carbon multiple bonds

151
Q

van der Waals’ forces

A

Very weak attractive forces between induced dipoles in neighbouring molecules.

152
Q

Volatility

A

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

153
Q

Water of crystallisation

A

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

A-level chemistry (15 decks)

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