A Level Chemistry Definitions Flashcards
(227 cards)
1
Q
acid
A
A species that releases H+ ions in aqueous solution
2
Q
acid dissociation constant Ka
A
The equilibrium constant that shows the extent of dissociation of a weak acid. For a weak acid HA(aq),
Ka = [H+(aq)][A-(AQ)]/[HA(aq)]
3
Q
acid-base pair
A
A pair of two species that transform into each other by gain or loss of a proton
4
Q
activation energy
A
The minimum energy required to start a reaction by the breaking of bonds
5
Q
actual yield
A
The amount of product obtained from a reaction
6
Q
addition polymerisation
A
Formation of a very long molecular chain, by repeating addition reactions of many unsaturated alkene molecules (monomers)
7
Q
addition reaction
A
A reaction in which two reactants join together to form one product
8
Q
adsorption
A
The process that occurs when a gas or liquid or solute is held to the surface of a solid
9
Q
alicyclic
A
Containing carbon atoms joined together in a ring that is not aromatic
10
Q
aliphatic
A
Containing carbon atoms joined together in straight or branched chains
11
Q
alkali
A
A type of base that dissolves in water forming hydroxide ions, OH-(aq) ions
12
Q
alkanes
A
The hydrocarbon homologous series with single carbon-to-carbon bonds and the general formula:
CnH2n+2
13
Q
alkenes
A
The hydrocarbon homologous series with at least one double carbon-to-carbon bonds and the general formula:
CnH2n
14
Q
alkyl group
A
A side chain formed by removing a hydrogen atom removed from an alkane parent chain, for example, CH3, C2H5; any alkyl group is often shown as R.
15
Q
alkynes
A
The hydrocarbon homologous series with at least one triple carbon-to-carbon bonds and the general formula:
CnH2n-2
16
Q
amount of substance
A
The quantity whose unit of the mole, used as a means of counting any species such as atoms, ions and molecules.
17
Q
anhydrous
A
Containing no water molecules
18
Q
anion
A
A negatively charged ion with more electrons than protons
19
Q
aromatic
A
Containing one or more benzene rings
20
Q
atom economy
A
(Sum of molar masses of desired products)/(sum of molar masses of all products)
A ~ 100%
21
Q
atomic (proton) number
A
The number of protons in the nucleus of an atom
22
Q
atomic orbital
A
A region around the nucleus that can hold up to two electrons, with opposite spins
23
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
24
Q
Avogadro constant NA
A
The number of atoms per mole of the carbon-12 isotope (6.02 x10^23 mol^-1)
25
base
A compound that neutralises an acid to form a salt
26
binary compound
A compound containing two elements only
27
bond angle
The angle between two bonds at an atom
28
bond dissociation enthalpy
The enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species
29
bonded pair
A pair of electrons shared between two atoms to make a covalent bond
30
Bronsted-Lowry acid
A species that is a proton, H+, donor
31
Bronsted-Lowry base
A species that is a proton, H+, acceptor
32
buffer solution
A system that minimises pH changes on addition of small amounts of an acid or a base
33
carbocation
An ion that contains a positively charged carbon atom
34
catalyst
A substance that increases the rate of a chemical reaction without being used up in the process; a catalyst provides an alternative route for the reaction with a lower activation energy
35
cation
A positively charged ion with fewer electrons than protons
36
chain reaction
A reaction in which the propagation steps release new radicals that continue the reaction
37
chemical shift δ
A scale, in ppm, that compares the frequency of an NMR absorption with the frequency of the reference TMS at δ = 0 ppm
38
chiral carbon
A carbon atom attached to four different atoms or groups of atoms
39
chromatogram
A visible record showing the result of separation of the components of a mixture by chromatography
40
cis-trans isomerism
A special type of E/Z isomerism in which there are two non-hydrogen groups and two hydrogen atoms around the C=C double bond: the cis isomer (Z isomer) has H atoms on each carbon on the same side; the trans isomer (E isomer) has H atoms on each carbon on different sides
41
closed system
A system isolated from its surroundings
42
collision theory
Two reacting particles must collide for a reaction to occur, and must be in the correct orientation and have sufficient energy to overcome the activation energy of the reaction
43
complex ion
A transition metal ion bonded to ligands by coordinate bonds (dative covalent bonds)
44
concentration
The amount of solute, in moles, dissolved in 1 dm^3 (1000cm^3) of solution
45
condensation reaction
A reaction in which two small molecules react together to form a larger molecule with elimination of a small molecule such as water
46
conjugate acid
A species that releases a proton to form a conjugate base
47
conjugate base
A species that accepts a proton to form a conjugate acid
48
coordinate bond
A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only; also called a dative covalent bond
49
coordination number
The total number of coordinate bonds formed between a central metal ion and its ligands
50
covalent bond
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
51
dative covalent
A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only; also called a coordinate bond
52
dehydration
An elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule
53
delocalised electrons
Electrons that are shared between more than two atoms
54
desorption
Release of an adsorbed substance from a surface
55
dipole
A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule, has a small positive charge δ+ and the other has a small negative charge δ-
56
displacement reaction
A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of its ions
57
displayed formula
A formula showing the relative positioning of all the atoms in a molecule and the bonds between them
58
disproportionation
A redox reaction in which the same element is both oxidised and reduced
59
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 and concentrations do not change
60
E/Z isomerism
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 rotation of the C=C bond
61
electron configuration
A shorthand representation that shows how electrons occupy sub-shells in an atom
62
electronegativity
A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
63
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
64
electrophilic addition
An addition reaction in which the first step is attack by an electrophile on a region of high electron density
65
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
66
elimination reaction
The removal of a molecule from a saturated molecule to make an unsaturated molecule
67
empirical formula
The formula that shows the simplest whole-number ratio of atoms of each element present in a compound
68
enantiomers
Stereoisomers that are non-superimposable mirror images of each other; also called optical isomers
69
end point
The point in a titration where the indicator changes colour; the end point indicates when the reaction is just complete
70
endothermic reaction
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 (∆H +ve).
71
enthalpy H
The heat content that is stored in a chemical system
72
enthalpy change ΔH
The difference between the enthalpy of the products and the enthalpy of the reactants
73
enthalpy cycle
A diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess' law
74
enthalpy profile diagram
A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products
75
entropy
The used for the dispersal of energy and disorder within the chemicals making up the chemical system
76
equilibrium constant Kc
A measure of the position of equilibrium; the magnitude of an equilibrium constant indicates whether there are more reactants or more products in an equilibrium system
77
equivalence point
The point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution
78
esterification
A reaction in which a carboxylic acid reacts with an alcohol to form an ester and water
79
exothermic reaction
A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (∆H -ve)
80
fingerprint region
An area of an infrared spectrum below 1500cm^-1 that gives a characteristic pattern for different compounds
81
first electron affinity
The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
82
first ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
83
fractional distillation
The separation of components in a liquid mixture by their different boiling points into fractions with different compositions
84
fragment ions
Ions formed from the breakdown of the molecular ion in a mass spectrometer
85
fragmentation
The process in mass spectrometry that causes a positive ion to split into smaller pieces, one of which is a positive fragment ion
86
free energy change ∆G
The balance between enthalpy, entropy and temperature for a process
∆G=∆H-T∆S
A process is feasible when ∆G<0
87
functional group
The part of the organic molecule responsible for its chemical reactions
88
general formula
The simplest algebraic formula of a member of a homologous series. For example, the general formula of the alkanes is CnH2n+2
89
giant covalent lattice
A three-dimensional structure of atoms, bonded together by strong covalent bonds
90
giant ionic lattice
A three-dimensional structure of oppositely charged ions, bonded together by strong ionic bonds
91
giant metallic lattice
A three-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bonds
92
group
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
93
half-life
The time taken for the concentration of a reactant to decrease by half
94
Hess' law
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
95
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
96
heterogeneous equilibrium
An equilibrium in which the species making up the reactants and products are in different physical states
97
heterolytic fission
The breaking of a covalent bond forming a cation (positive ion) and an anion (negative ion)
98
homogeneous catalysis
A reaction in which the catalyst and reactants are in the same physical state, which is most frequently the aqueous or gaseous state
99
homogeneous equilibrium
An equilibrium in which all the species making up the reactants and products are in the same physical state
100
homologous series
A series of organic compounds with the same functional group but with each successive member differing by CH2
101
homolytic fission
The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals
102
hydrated
A crystalline compound containing water molecules
103
hydrocarbon
A compound composed of only carbon and hydrogen
104
hydrogen bond
A strong dipole-dipole attraction between an electron-deficient hydrogen atom of -NH, -OH, or HF on one molecule and a lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule
105
hydrolysis
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
106
induced dipole-dipole interaction
Attractive forces between induced dipoles in different molecules - also called London Forces
107
infrared spectroscopy
An instrumentation method of analysis that identifies bonds from absorption of the infrared radiation of different wavelengths
108
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
109
initiation
The first stage in a radical reaction in which radicals start when a covalent bond is broken by homolytic fission of a covalent bond
110
intermediate
A species formed during a reaction that reacts further and is not present in the final products
111
intermolecular force
An attractive force between molecules. Intermolecular forces can be London forces, permanent dipole-dipole interactions or hydrogen bonding
112
ion
A positively or negatively charged atom or a (covalently bonded) group of atoms (a polyatomic ion), where the number of electrons is different from the number of protons
113
ionic bonding
The electrostatic attraction between oppositely charged ions
114
ionic product of water Kw
The product of the ions formed in the partial dissociation of water, given by Kw = [H+(aq)] [OH-(aq)]
115
isotopes
Atoms of the same element with different numbers of neutrons and different masses
116
lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions
117
Le Chatelier's Principle
When a system in dynamic equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of the change and to restore equilibrium
118
ligand
A molecule or ion that can donate a pair of electrons to the transition metal ion
119
ligand substitution
A reaction in which one or more ligands in a complex ion are replaced by different ligands
120
limiting reagent
The reactant that is not in excess, which will be used up first and stop the reaction
121
lone pair
An outer shell pair of electrons that is not involved in chemical bonding
122
mass number
The sum of the number of protons and neutrons in the nucleus - also known as nucleon number
123
metallic bond
The electrostatic attraction between positive metal ions and delocalised electrons
124
mobile phase
The phase that moves in chromatography
125
molar gas volume Vm
The volume per mole of gas molecules at a stated temperature and pressure
126
molar mass M
The mass mole of a substance in units of g mol-1
127
mole
The amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12g of the carbon-12 isotope, that is, 6.02 x10^23 particles
128
molecular formula
A formula that shows the number and type of atoms of each element present in a molecule
129
molecular ion
The positive ion formed in mass spectrometry when a molecule loses an electron
130
molecule
The smallest part of a covalent compound that can exist while retaining its chemical identity, consisting of two or more atoms covalently bonded together
131
monomer
A small molecule that combines with many other monomers to form a polymer
132
neutralisation
A chemical reaction in which an acid and a base react together to produce a salt and water
133
nomenclature
A system of naming compounds
134
non-polar
With no charge separation across a bond or in a molecule
135
nucleophile
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
136
nucleophilic substitution
A reaction in which a nucleophile is attracted to an electron-deficient carbon atom, and replaces an atom or group of atoms on the carbon atom
137
optical isomers
Stereoisomers that are non-superimposable mirror images of each other; also called 'enantiomers'
138
order
The power to which the concentration of a reactant is raised in the rate equation
139
overall order
The sum of the individual orders of reactants in the rate equation: m + n
140
oxidation
Loss of electrons or an increase in oxidation number
141
oxidation number
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
142
oxidation state
The oxidation number
143
oxidising agent
A reagent that oxidises (takes electrons from) another species
144
π-bond
A bond formed by the sideways overlap of two p-orbitals, with the electron density above and the plane of the bonding atoms
145
partial dissociation
The splitting of some of a species in solution into aqueous ions
146
Pauling electronegativity value
A value assigned as a measure of the relative attraction of a bonded atom for the pair of electrons in a covalent bond
147
percentage yield
% yield = (actual amount, in mol, of product) / (theoretical amount, in mol, of product) x 100
148
period
A horizontal row of elements in the periodic table. Elements show trend in properties across a period
149
periodicity
A repeating trend in properties of the elements across each period of the periodic table
150
permanent dipole
A small charge difference that does not change across a bond, with δ+ and δ- partial changes on the bonded atoms: the result of the bonded atoms having different electronegativities
151
Permanent dipole-dipole interaction
An attractive force between permanent dipoles in neighbouring polar molecules
152
pH
The expression:
| pH = -log[H+(aq)]
153
polar (molecule)
With δ+ and δ- charges at different ends of the molecule
154
polar covalent bond
A bond with a permanent dipole, having δ+ and δ- partial changes on the bonded atoms
155
polar molecule
A molecule with an overall dipole, having taken into account any dipoles across bonds and the shape of the molecule
156
polyatomic ion
An ion containing more than one atom
157
polymer
A large molecule formed from many thousands of repeat units of smaller molecules known as monomers
158
position of equilibrium
The relative quantities of reactants and products, indicating the extent of a reversible reaction at equilibrium
159
precipitation reaction
The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together
160
primary
On a carbon atom at the end of a chain
161
primary alcohol
An alcohol in which the OH group is attached to a carbon atom that is attached to two or three hydrogen atoms
162
principal quantum number n
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
163
propagation
The steps that continue a free radical reaction, in which a radical reacts with a reactant molecule to form a new molecule and another radical, causing a chain reaction
164
proton number
The number of protons in the nucleus of an atom; also known as atomic number
165
radical
A species with an unpaired electron
166
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
167
rate equation
For a reaction: A + B → C with orders m for A and n for B, the rate equation is given by:
rate = k[A]^m[B]^n
168
rate-determining step
The slowest step in the reaction mechanism of a multi-step reaction
169
reaction mechanism
The sequence of bond breaking and bond-forming steps that shows the path taken by electrons during a reaction
170
redox reaction
A reaction involving reduction and oxidation
171
reducing agent
A reagent that reduces (adds electrons to) another species
172
reduction
Gain of electrons or a decrease in oxidation number
173
reflux
The continual boiling and condensing of a reaction mixture back to the original container to ensure that the reaction takes place without the contents of the flask boiling dry
174
relative atomic mass Ar
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12
175
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
176
relative isotopic mass
The mass of an atom of an isotope compared with one twelfth of the mass of an atom of carbon-12
177
relative molecular mass
The weighted mean mass of a molecule of a compound compared with one twelfth of the mass of an atom of carbon-12
178
repeat unit
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
179
retention time
In gas chromatography, it is the time for a component to pass from the column inlet to the detector
180
reversible reaction
A reaction that takes place in both forward and reverse directions
181
Rf value
Rf = distance moved by component / distance moved by solvent
182
σ bond
A bond formed by the overlap of one orbital from each bonding atom, consisting of two electrons and with the electron density centred around a line directly between the nuclei of the two atoms
183
salt
The product of a reaction in which the H- ions from the acid are replaced by metal or ammonium ions
184
saturated
Containing single bonds only
185
saturated hydrocarbon
A hydrocarbon with single bonds only
186
second electron affinity
The enthalpy change that takes place when one electron is added to each ion in one mole of gaseous 1- ions to form one mole of gaseous 2- ions
187
second ionisation energy
The energy needed to remove 1 electron from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions
188
secondary
On a carbon atom to which two carbon chains are attached
189
secondary alcohol
An alcohol in which the -OH group is attached to a carbon atom that is attached to two carbon chains and one hydrogen atom
190
shell
A group of atomic orbitals with the same principal quantum number, n. Also known as a main energy level
191
shielding effect
The repulsion between electrons in different inner shells. Shielding reduces the net attractive force between the positive nucleus on the outer shell electrons
192
simple molecular lattice
A three-dimensional structure of molecules, bonded together by weak intermolecular forces
193
skeletal formula
A simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups
194
specific heat capacity c
The energy required to raise the temperature of 1 g of a substance by 1 °C
195
spectator ions
Ions that are present but take no part in a chemical reaction
196
spin-spin coupling
In an NMR spectrum, the interaction between spin states of non-equivalent nuclei that results in the splitting of a signal
197
standard conditions
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)
198
standard electrode potential E
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 100kPa
199
standard enthalpy change of atomisation
The enthalpy change that takes place when one mole of gaseous atoms forms from the element it its standard state
200
standard enthalpy change of combustion ∆cH
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states
201
standard enthalpy change of formation ∆fH
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
202
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
203
standard enthalpy change of neutralisation ∆neutH
The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O (l), under standard conditions, with all reactants and products in their standard states
204
standard enthalpy change of reaction ∆rH
The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, with all reactants and products in their standard states
205
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
206
standard solution
A solution of known concentration
207
standard state
The physical state of a substance under standard conditions of 100 kPa and a stated temperature (usually 298 K)
208
stationary phase
The phase that does not move in chromatography
209
stereoisomers
Compounds with the same structural formula but with a different arrangement of the atoms in space
210
stoichiometry
The ratio of the amount, in moles, of each substance in a chemical equation (essentially the ratio of the balancing numbers)
211
strong acid
An acid that dissociates completely in solution
212
structural formula
A formula showing the minimal detail for the arrangement of atoms in a molecule
213
structural isomers
Molecules with the same molecular formula but with different structural formulae
214
sub-shell
A group of orbitals of the same type within a shell
215
substitution reaction
A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms
216
surroundings
Everything that is not the chemical system
217
system
The chemicals involved in the reaction
218
termination
The step at the end of a radical substitution when two radicals combine to form a molecule
219
tertiary alcohol
An alcohol in which the hydroxyl (-OH) group is attached to a carbon that is in turn attached to three other carbon atoms and no hydrogen atoms
220
theoretical yield
The yield resulting from complete conversion of reactants into products
221
thermal decomposition
The breaking up of a chemical substance with heat into at least two chemical substances
222
titre
The volume added from the burette when the volume of one solution has exactly reacted with the other solution
223
transition element
A d-block element which forms an ion with an incomplete d-sub-shell
224
unsaturated
Containing a multiple carbon-carbon bond
225
volatility
The ease at which a liquid turns into a gas. Volatility increases as boiling point decreases
226
water of crystallisation
Water molecules that are bonded into a crystalline structure of a compound
227
weak acid
An acid that dissociates only partially in solution
