Glossary Flashcards
acid
a species that releases H+ ions in aqueous solution
acid dissociation constant Ka
the equilibrium constant that shows the extent of
dissociation of a weak acid
acid–base 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
actual yield
the amount of product obtained from a reaction
addition polymerisation
formation of a very long molecular chain, by repeated addition reactions of many unsaturated alkene molecules (monomers)
addition reaction
a reaction in which a reactant is added to an unsaturated molecule to make a one saturated molecule
adsorption
the process that occurs when a gas or liquid or solute is held to the surface of a solid
alicyclic
containing carbon atoms joined together in a ring that is not aromatic
aliphatic
containing carbon atoms joined together in straight or branched chains
alkali
a type of base that dissolves in water forming hydroxide ions, OH–(aq) ions
alkanes
the hydrocarbon homologous series with single carbon-to-carbon bonds and the general formula: CnH2n+2
alkenes
the hydrocarbon homologous series with at one double carbon-to-carbon bonds and the general formula: CnH2n
alkyl group
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
alkynes
the hydrocarbon homologous series with one triple carbon-to-carbon bonds and the general formula: CnH2n–2
amount of substance
the quantity whose unit of the mole, used as a means of counting any species such as atoms, ions and molecules
anhydrous
containing no water molecules
anion
a negatively charged ion with more electrons than protons
aromatic
containing one or more benzene rings
atom economy
(sum of molar masses of desired products)/(sum of molar masses of all products) Å~100%
atomic (proton) number
the number of protons in the nucleus of an atom
atomic orbital
a region around the nucleus that can hold up to two electrons, with opposite spins
average bond enthalpy
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
Avogadro constant NA
the number of atoms per mole of the carbon-12 isotope. (6.02 × 1023 mol–1)
base
a compound that neutralises an acid to form a salt
binary compound
a compound containing two elements only
bond angle
the angle between two bonds at an atom
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.
bonded pait
a pair of electrons shared between two atoms to make a covalent bond
Brønsted–Lowry acid
a species that is a proton, H+, donor
Brønsted–Lowry 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 a base
carbocation
an ion that contains a positively charged carbon atom
catalyst
a substance that increases the rate of a chemical reaction without being used up in the process; a catalyst provide an alternative route for the reaction with lower activation energy
cation
a positively charged ion with fewer electrons than protons
chain reaction
a reaction in which the propagation steps release new radicals that continue the reaction
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
chiral carbon
a carbon atom attached to four different atoms or groups of atoms
chromatogram
a visible record showing the result of separation of the components of a mixture by chromatography
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
closed system
a system isolated from its surroundings
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
complex ion
a transition metal ion bonded to ligands by coordinate bonds (dative covalent bonds)
concentration
the amount of solute, in moles, dissolved in 1 dm3 (1000 cm3) of solution
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
conjugate acid
a species that releases a proton to form a conjugate base
conjugate base
a species that accepts a proton to form a conjugate acid
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
coordination number
the total number of coordinate bonds formed between a central metal ion and ligands
covalent bond
the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
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
dehydration
an elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule
delocalised electrons
electrons that are shared between more than two atoms
desorption
release of an adsorbed substance from a surface
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–.
displacement reaction
a reaction in which a more reactive element displaces a less reactive element from an aqueous solution of its ions
displayed formula
a formula showing the relative positioning of all the atoms in a molecule and the bonds between them
disproportionation
a redox reaction in which the same element is both oxidised and reduced
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
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
electron configuration
a shorthand representation that shows how electrons occupy sub-shells in an atom
electronegativity
a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
electrophile
an atom (or group of atoms) which is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond
electrophilic addition
an addition reaction in which the first step is attack by an electrophile on a region of high electron density
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
elimination reaction
the removal of a molecule from a saturated molecule to make an unsaturated molecule
empirical formula
the formula that shows the simplest whole-number ratio of atoms of each element present in a compound
enantiomers
stereoisomers that are nonsuperimposable mirror images of each other; also called optical isomers
end point
the point in a titration where the indicator changes colour; the end point indicates when the reaction is just complete
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 (ΔH is positive)
enthalpy H
the heat content that is stored in a chemical system
enthalpy change ΔH
the difference between the enthalpy of the products and the enthalpy of the reactants.
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’s law
enthalpy profile diagram
a diagram for a reaction to compares the enthalpy of the reactants with the enthalpy of the products
entropy
the used for the dispersal of energy and disorder within the chemicals making up the chemical system
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
equivalence point
the point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution
esterification
a reaction in which a carboxylic acid reacts with an alcohol to form an ester and water
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 (ΔH is negative)
fingerprint region
an area of an infrared spectrum below 1500 cm–1 that gives a characteristic pattern for different compounds
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
first ionisation energy
the energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
fractional distillation
the separation of components in a liquid mixture by their different boiling points into fractions with different compositions
fragment ions
ions formed from the breakdown of the molecular ion in a mass spectrometer
fragmentation
the process in mass spectrometry that causes a positive ion to spilt into smaller pieces, one of which is a positive fragment ion
free energy change ΔG
the balance between enthalpy, entropy and temperature for a process given by ΔG = ΔH − TΔS. A process is feasible when ΔG < 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
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 strong ionic bonds
giant metallic lattice
a three-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bonds
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
half-life
the time taken for the concentration of a reactant to decrease by half
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
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 have different physical states
heterolytic fission
the breaking of a covalent bond with both of the bonded electrons going to each atom, forming a cation (positive ion) and an anion (negative ion)
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
homogeneous equilibrium
an equilibrium in which all the species making up the reactants and products have the same physical state
homologous series
a series of organic compounds with the same functional group but with each successive member differing by CH2
homolytic fission
the breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals
hydrated
a crystalline compound containing water molecules
hydrocarbon
a compound of hydrogen and carbon only
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
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
induced dipole–dipole interaction
attractive forces between induced dipoles in different molecules – also called London Forces
infrared spectroscopy
an instrumentation method of analysis that identifies bonds from absorption of the infrared radiation of different wavelengths
initial rate of reaction
the change in concentration of a reactant or product per unit time at the start of the reaction: t = 0.
initiation
the first stage in a radical reaction in which radicals starts when a covalent bond is broken by homolytic fission of a covalent bond
intermediate
a species formed during a reaction that reacts further and is not present in the final products
intermolecular force
an attractive force between molecules. Intermolecular forces can be London forces, permanent dipole-dipole interactions or hydrogen bonding
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
ionic bonding
the electrostatic attraction between positive and negative ions
ionic product of water Kw
the product of the ions formed in the partial dissociation of water, given by Kw = [H+(aq)] [OH−(aq)]
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 ionic compound from its gaseous ions under standard conditions
Le Chatelier’s principle
when a system in dynamic equilibrium is subjected to a external change, the system readjusts 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 the transition metal ion
ligand substitution
a reaction in which one or more ligands in a complex ion are replaced by different ligands
limiting reagent
the reactant that is not in excess, which will be used up first and stop the reaction.
lone pair
an outer shell pair of electrons that is not involved in chemical bonding
mass number
the sum of the number of protons and neutrons in the nucleus – also known as nucleon number
metallic bond
the electrostatic attraction between positive metal ions and delocalised electrons
mobile phase
the phase that moves in chromatography
molar gas volume Vm
the volume per mole of gas molecules at a stated temperature and pressure
molar mass M
the mass per mole of a substance, in units of g mol−1
mole
the amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12 g of the carbon-12 isotope, that is, 6.02 × 10 to the power of 23 particles
molecular formula
a formula that shows the number and type of atoms of each element present in a molecule
molecular ion
the positive ion formed in mass spectrometry when a molecule loses an electron
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
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
nomenclature
a system of naming compounds
non-polar
with no charge separation across a bond or in a molecule
nucleophile
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
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
optical isomers
stereoisomers that are nonsuperimposable mirror images of each other; also called ‘enantiomers’
order
the power to which the concentration of a reactant is raised in the rate equation
overall order
the sum of the individual orders of reactants in the rate equation: 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 of another element. Oxidation numbers are derived form a set of rules
oxidation state
the oxidation number
oxidising agent
a reagent that oxidises (takes electrons from) another species
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
partial dissociation
the splitting of some of a species in solution into aqueous ions.
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
percentage yield
% yield =
(actual amount, in mol, of product / theoretical amount, in mol, of product)
× 100
period
a horizontal row of elements in the periodic table. Elements show trend in properties across a period
periodicity
a repeating trend in properties of the elements across each period of the periodic table
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 electrongativities
permanent dipole–dipole interaction
an attractive force between permanent dipoles in neighbouring polar molecules
pH
the expression, pH = −log[H+(aq)].
polar (molecule)
with δ+ and δ− charges at different ends of the molecule
polar covalent bond
a bond with a permanent dipole, having δ+ and δ− partial changes on the bonded atoms
polar molecule
a molecule with an overall dipole, having taken into account any dipoles across bonds and the shape of the molecule
polyatomic ion
an ion containing more than one atom
polymer
an large molecule formed from many thousands of repeat units of smaller molecules known as monomers
position of equilibrium
the relative quantities of reactants and products, indicating the extent of a reversible reaction at equilibrium
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
primary
on a carbon atom at the end of a chain
primary alcohol
an alcohol in which the OH group is attached to a carbon atom that is attached to two or three hydrogen atoms
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
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
proton number
the number of protons in the nucleus of an atom; also known as atomic number
radical
a species with an unpaired electron
rate constant k
the constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation
rate equation
for 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
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
reaction mechanism
the sequence of bond breaking and bond-forming steps that shows the path taken by electrons during a reaction
redox reaction
a reaction involving reduction and oxidation
reducing agent
a reagent that reduces (adds electron to) another species
reduction
gain of electrons or a decrease in oxidation number
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
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
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 an atom of carbon-12
relative molecular mass Mr
the weighted mean mass of a molecule of a compound compared with one-twelfth of 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 of which is the symbol n.
retention time
in gas chromatography. The time for a component to pass from the column inlet to the detector
reversible reaction
a reaction that takes place in both forward and reverse directions
Rf value
Rf =
distance moved by component / distance moved by solvent
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
salt
the product of a reaction in which the H− ions from the acid are replaced by metal or ammonium ions
saturated
containing single bonds only
saturated hydrocarbon
a hydrocarbon with single bonds only
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
second ionisation energy
the energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions.
secondary
on a carbon atom to which two carbon chains are attached
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
shell
a group of atomic orbitals with the same principal quantum number, n. Also known as a main energy level
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
simple molecular lattice
a three-dimensional structure of molecules, bonded together by weak intermolecular forces
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 1 g of a substance by 1 °C
spectator ions
ions that are present but take no part in a chemical reaction
spin-spin coupling
in an NMR spectrum, the interaction between spin states of non-equivalent nuclei that results in the splitting of a signal
standard conditions
a pressure of 100 kPa, a stated temperature, usually 298 K (25 °C) and a concentration of 1 mol dm−3 (for reactions with aqueous solutions).
standard electrode potential Eɵ
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 100 kPa
standard enthalpy change of atomisation
the enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state
standard enthalpy change of combustion ΔcHɵ
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
standard enthalpy change of formation ΔfHɵ
the enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.
standard enthalpy change of hydration
the enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions
standard enthalpy change of neutralisation ΔneutHɵ
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
standard enthalpy change of reaction ΔrHɵ
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
standard enthalpy change of solution
the enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions
standard solution
a solution of known concentration
standard state
the physical state of a substance under standard conditions of 100 kPa and a stated temperature (usually 298 K).
stationary phase
the phase that does not moves in chromatography
stereoisomers
compounds with the same structural formula but with a different arrangement of the atoms in space
stoichiometry
the ratio of the amount, in moles, of each substance in a chemical equation (essentially the ratio of the balancing numbers)
strong acid
an acid that dissociates completely in solution
structural formula
a formula showing the minimal detail for the arrangement of atoms in a molecule
structural isomers
molecules with the same molecular formula but with different structural formulae
sub-shell
a group of orbitals of the same type within a shell
substitution reaction
a reaction in which an atom or group of atoms is replaced with a different atom or group of atoms
surroundings
everything that is not the chemical system
system
the chemicals involved in the reaction
termination
the step at the end of a radical substitution when two radicals combine to form a molecule
tertiary alcohol
an alcohol in which the −OH group is attached to a carbon atom that is attached to three carbon atoms and no hydrogen atoms
theoretical yield
the yield resulting from complete conversion of reactants into products
thermal decomposition
the breaking up of a chemical substance with heat into at least two chemical substances
titre
the volume added from the burette when the volume of one solution has exactly reacted with the other solution
transition element
a d-block element which forms an ion with an incomplete d-sub-shell
unsaturated
containing a multiple carbon-carbon bond
volatility
the ease at which a liquid turns into a gas. Volatility increases as boiling point decreases
water of crystallisation
water molecules that are bonded into a crystalline structure of a compound
weak acid
an acid that dissociates only partially in solution
