Chemistry definitions

• Relative atomic mass

  The average mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12
• Relative isotopic mass

  The mass of an atom of an isotope of an element relative to 1/12 of the mass of an atom of carbon-12
• Relative molecular mass

  the sum of the relative atomic masses of the atoms in the molecule
• Empirical formula

  The simplest whole number ratio of atoms of each element present in a compound
• enthalpy change

  Heat energy change for a reaction at constant pressure
• mean bond enthalpy


  the average energies required to break one mole of a bond from a variety of molecules in the gas state
• standard enthalpy of formation


  enthalpy change when 1 mole of a chemical is formed from its elements under standard conditions with all reactants and products in their standard states
• standard enthalpy of combustion


  enthalpy change when 1 mole of a chemical is burnt completely in excess oxygen with all reactants and products in their standard states under standard conditions
• first ionisation energy

  The energy required to remove one electron from a mole of gaseous atoms to form one mole of gaseous 1+ ions
• second ionisation energy

  The energy required to remove one electron from a mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.
• electronegativity

  the power of an atom to attract electron density towards itself in a covalent bond
• covalent bonding

  electrostatic attraction between positive nuclei and shared pair of electrons
• coordinate bond

  A covalent bond in which both electrons in the shared pair come from the same atom.
• metallic bonding

  electrostatic attraction between sea of delocalised electrons and positive ions in a layered structure
• cracking

  a process where long chain hydrocarbon molecules are broken into shorter chain molecules which are in high demand
• homologous series

  family of organic compounds with the same general formula and same functional group
• structural isomer


  Compounds that have the same molecular formula but different arrangements of atoms.
• stereoisomer


  compound with the same molecular and structural formulas but different arrangement in space
• nucleophile


  electron pair donor
• electrochemical series


  A list of elements in order of their standard electrode potentials
• mechanism


  step by step pathway for a reaction
• electrophile


  electron pair acceptor
• carbon neutral


  making no net release of carbon dioxide to the atmosphere,
• titration


  A solution of known concentration is used to determine the concentration of another solution.
• hess's law


  the enthalpy change for a process is independent to the route taken
• Le Chatilier's Principle


  if a change is made to a system at equilibrium, the equilibrium will shift to counteract this change
• periodicity


  the repeating pattern of chemical and physical properties of the elements
• Maxwell Boltzmann distributions


  show us the energies of all the particles in a system
• reaction rate


  the change in concentration of any reactants or products per unit time
• chiral centre


  carbon with four different substituents
• racemic mixture


  a mixture of equal amounts of two enantiomers
• integration


  how many hydrogens are in each environment
• splitting patterns


  these are caused by hydrogens interacting with each other
• chromatography


  A technique that is used to separate the components of a mixture by passing it in a solution or suspension through a medium in which the components move at different rates
• biodiesel


  A diesel substitute produced by extracting and chemically altering oil from plants
• primary structure


  sequence of amino acids
• secondary structure


  hydrogen bonds form between amides
• tertiary structure


  how the protein is folded and held together by interactions between side chains
• DNA


  double helix with complementary strands
• electron affinity


  enthalpy change when one mole of gaseous atoms gain an electron to form 1 mole of gaseous 1- ions