definitions

• isotope is an atom with the same number of protons but different numbers of neutrons
• relative atomic mass


  average mass of an atom of an element

  ---------------------------------

  1/12th mass of an atom of c12
• relative molecular mass


  average total mass of a molecule

  -------------------------------

  1/12th mass of an atom of c12
• orbitals


  region of an atom that can hold up to two electrons with opposite spins
• atomic radius


  the distance between the nucleus and outermost electron
• ionisation energy


  minimum energy required to remove one mole of electrons from one mole of atoms in the gaseous state to form one mole of unipositive ions
• empirical formula

  simplest whole number ratio of each atom of an element in a molecule
• molecular formula

  actual number of each atom in a molecule
• ionic bonding


  strong electrostatic force of attraction between oppositely charged ions
• metallic bonding


  electrostatic force of attraction between positive metal ions and delocalised electrons
• covalent bonding


  A bond formed by a shared pair of electrons
• dative covalent bonds


  A bond formed by a shared pair of electrons where both electrons come from one atom
• electronegativity 


  the power of an atom to attract a pair of electrons in a covalent bond
• homologous series 


  family of molecules which all contain the same functional group, but each successive member differs by CH2
• saturated compounds


  compounds containing only single C-C bonds
• unsaturated compounds 


  compounds containing multiple C-C bonds, C=C, C triple bond C or an aromatic ring
• hydrocarbon 


  compound containing only hydrogen and carbon atoms
• structural isomerism 


  molecules with the same molecular formula but a different structural formula
• chain isomerism 


  different arrangement of the carbon skeleton, straight and branched chains
• position isomerism


  movement of the functional group
• functional group isomerism


  different functional group
• stereoisomerism


  same structural formula but atoms are arranged differently in space
• free radical

  species with a single unpaired electron
• substitution reaction 


  atom or a group of atoms are replaced with a different atom or group of atoms
• nucleophile 


  electron pair donor
• electrophile 


  electron pair acceptor
• definition of mass number


  total number of protons and neutrons in an atom
• definition of atomic mass


  number of protons in the nucleus
• definition of enthalpy change


  change in heat energy measured at constant pressure
• definition of standard enthalpy of formation


  enthalpy change when one mole of a compound is formed from its elements

  where all reactants and products are in their standard states under standard conditions.
• definition of standard enthalpy change of combustion 


  enthalpy change when one mole of a substance is burned in excess oxygen

  with all reactants and products in their standard states under standard conditions.
• Hess’ law


  enthalpy change for a chemical reaction is independent of the route taken
• mean bond enthalpy


  average energy required to separate completely the atoms in one mole of covalent bonds in the gas phase
• definition of rate of reaction 


  change in conc of a reactant or product per unit time
• definition of activation energy 


  minimum energy required for particles to react upon collision
• definition of catalyst


  substance that increases rate of reaction and remains chemically unchanged at end of reaction