AS Chemistry Glossary

Complete glossary of essential terms for as chemistry, applicaticable for all as chemistry exam boards. 

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AS Chemistry (OCR) Glossary
Acid- A species that is a proton donor
Activation Energy- The minimum energy required to start a reaction by the breaking of
Addition Polymer- A very long molecular chain, formed by repeated addition reactions of
many unsaturated alkene molecules (monomers)
Addition Polymerisation- 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)
Addition Reaction- A reaction in which a reactant is added to an unsaturated molecule to
make a saturated molecule
Adsorption- The process that occurs when a gas, liquid or solute is held to the surface of a
solid, or more rarely a liquid
Alicyclic Hydrocarbon- A hydrocarbon with carbon atoms in a ring structure
Aliphatic Hydrocarbon- A hydrocarbon chain with carbon atoms joined together in
straight or branched chains
Alkali- A type of base that dissolves in water forming hydroxide ions
Alkanes- The homologous series with the general formula CnH2n+2
Alkyl Group- AN alkane with a hydrogen atom removed
Amount of Substance- The quantity whose unit is the mole. Chemists use `amount of
substance' as a means of counting atoms
Anhydrous- A substance containing no water molecules
Anion- A negatively charged ion
Atom Economy- Molecular mass of desired product/Sum of all product masses x100
Atomic Orbital- A region within an atom that can hold up to two electrons with opposite
Atomic (Proton) Number- The number of protons in the nucleus of an atom
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, N- Number of atoms per mol of the carbon-12 isotopes, 6.02x1023
Base- A species that is a proton acceptor
Biodegradable Material- A substance that is broken down naturally in the environment by
living organisms
Boltzmann Distribution- The distribution of energies of molecules at a particular
temperature, usually shown as a graph
Bond 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
Carbanion- An organic ion in which a carbon atom has a negative charge
Carbocation- An organic ion in which a carbon atoms has a positive charge
Catalyst- A substance that increases the rate of a chemical reaction without being used
up in the process

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Cation- A positively charged ion
Cis-Trans Isomerism- A special type of E/Z isomerism in which there is a non-hydrogen
group and a hydrogen on each C of a C=C double bond. This cis/Z isomer has the H atoms
on the same side.…read more

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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
Enthalpy- The heat content that is stored in a chemical system
Enthalpy Change of Combustion- The enthalpy change that takes place when one mole
of a substance reacts completely with oxygen under standard conditions, all reactants
being in their standard states
Enthalpy Change of Formation-The enthalpy change that takes place when one mole of a
compound in…read more

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Heterolytic Fission- The breaking of a covalent bond with both of the bonded electrons
going to one of the atoms, forming a cation and an anion
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
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…read more

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Molecular Ion- The positive ion formed in mass spectrometry when a molecule loses an
Molecule- A small group of atoms held together by covalent bonds
Monomer- A small molecule that combines with many other monomers to form a polymer
Nomenclature- A system of naming compounds
Nucleophile- An atom that is attracted to an electron deficient center or atom, where it
donates a pair of electrons to form a new covalent bond
Nucleophilic Substitution- A type of substitution reaction in which a nucleophile is
attracted…read more

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Reflux- The continual boiling and condensing of a reaction mixture to ensure that the
reaction takes place without the contents of the flask boiling dry
Relative Atomic Mass- The weighted mean 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 a formula unit compared with one
twelfth of the mass of an atom of carbon 12
Relative Isotopic Mass- The mass of an atom of an isotope…read more

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Termination- The step at the end of a radical substitution when two radicals combine to
form a molecule
Thermal Decomposition- The breaking up of a chemical substance with heat into at least
two chemical substances
Troposphere- The lowest layer of the Earth's atmosphere, extending from the earth's
surface up to about 7km above the poles and 20km above the tropics
Unsaturated Hydrocarbon- A hydrocarbon containing carbon-carbon multiple bonds
Van der Waals' Forces- Very weak attractive forces between induced dipoles in
neighbouring molecules
Volatility- The ease…read more


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