A Level Chemistry Definitions Flashcards
Isotopes
Atoms of the same element with different numbers of neutrons and different mass numbers.
Relative Isotopic Mass
The mass of an isotope compared with 1/12 of the mass of an atom of carbon-12.
Relative Atomic Mass
The weighted mean mass of an atom compared with 1/12 of the mass of an atom of carbon-12.
Mole
The amount of substance that contains 6.02 x 10^23 (Avogadro’s number) particles.
Empirical Formula
The simplest whole number ratio of atoms of each element present in a compound.
Molecular Formula
The number and type of atoms of each element present in a molecule.
Anhydrous
A compound that doesn’t contain any water of crystallisation.
Hydrated
A compound that contains water(s) of crystallisation.
Water Of Crystallisation
Water molecules that form an essential part of a compound’s crystalline structure.
Acid
A substance that releases H+ ions in aqueous solution.
Alkali
A substance that releases OH- ions in aqueous solution.
Weak Acid
An acid that partially dissociates in solution.
Strong Acid
An acid that fully dissociates in solution.
Orbital
A region around the nucleus that can hold up to 2 electrons in opposite spin.
Ionic Bonding
Electrostatic attraction between oppositely charged ions.
Covalent Bonding
Electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
Dative Bond
A covalent bond where both of the shared electrons are donated by one of the bonding atoms.
Electronegativity
The ability of an atom to attract a shared pair of electrons in a covalent bond.
Periodicity
Repeating trends in physical/chemical properties across periods of the periodic table.
First Ionisation Energy
The amount of energy required to remove one mole of electrons from one mole of gaseous atoms in order to form one mole of gaseous 1+ ions.
Metallic Bonding
Electrostatic attraction between metal cations and delocalised electrons.
Disproportionation
Oxidation and reduction of the same element in a reaction.
Exothermic
More energy is released forming bonds than energy taken in breaking bonds.
Endothermic
More energy is taken in breaking bonds than energy released forming bonds.
Enthalpy
A measurement of the amount of thermal energy within a system.
Activation Energy
The minimum amount of energy a particle needs in order to react.
Enthalpy Change Of Formation
The enthalpy change when forming one mole of a compound from its elements in their standard states under standard conditions.
Enthalpy Change Of Combustion
The enthalpy change when one mole of substance undergoes complete combustion/reacts with excess oxygen under standard conditions.
Enthalpy Change Of Neutralisation
The enthalpy change when one mole of water is formed by an acid and an alkali under standard conditions.
Average Bond Enthalpy
The amount of energy required to break 1 mole of bonds in gaseous molecules.
Catalyst
A substance that increases the rate of reaction without being used up in the overall reaction by providing an alternative reaction pathway with a lower activation energy.
Homogeneous Catalyst
Catalyst in the same state as the reactants.
Heterogeneous Catalyst
Catalyst in a different state to the reactants.
Dynamic Equilibrium
A closed system where the rate of the forward reaction is equal to the rate of the reverse reaction.
Homologous Series
A series of organic compounds with the same functional group where each successive member differs by CH2.
Functional Group
The group of atoms responsible for the characteristic reactions of a compound.
Aliphatic Compound
A compound containing C/H atoms joined together in straight/branched chains or non-aromatic rings.
Alicyclic Compound
An aliphatic compound arranged in a non-aromatic ring.
Aromatic Compound
A compound that contains a benzene ring.
Unsaturated
Contains a C=C or C≡C or benzene ring.
Saturated
Doesn’t contain any C=C or C≡C bonds.
Structural Isomers
Compounds with the same molecular formula but different structural formulae.
Stereoisomers
Compounds with the same structural formula but different spatial arrangements.
Homolytic Fission
The breaking of a covalent bond where each bonded atom receives 1 electron from the shared pair forming 2 radicals.
Heterolytic Fission
The breaking of a covalent bond where one of the bonded atoms receives both electrons from the shared pair.
Radical
A species that contains an unpaired electron.
Electrophile
A species that accepts a pair of electrons in order to form a covalent bond.
Nucleophile
A species that donates a pair of electrons in order to form a covalent bond.
Pi Bond Formation
Sideways overlap of adjacent p-orbitals above and below the bonding carbon atoms.
E/Z Isomerism
Stereoisomerism caused by the restricted rotation around a C=C double bond when there are 2 different groups attached to each of the carbon atoms.
Cis-Trans Isomerism
A special case of E/Z isomerism in which there is an identical group attached to both carbon atoms of the C=C bond.
Standard Conditions
298K & 101KPa
SI Volume
SI Pressure
SI Temperature
SI Mass
m^3
Pa
K
Kg
Lattice enthalpy
The energy released when 1 mole of an ionic compound is formed from its constituent ions in their gaseous state under standard conditions.
enthalpy change of solution
The enthalpy change that takes place when 1 mole of a solute is completely dissolved in water under standard conditions.
enthalpy change of hydration
The energy released when 1 mole of gaseous ions are dissolved in water under standard conditions.
entropy
A measure of the dispersal of energy within a system.
