redox, oxidation & reduction

• • oxidation is the loss of electrons
  • reduction is the gain of electrons
• oxidation state- the number of electrons the atom has lost or gained when it formed a chemical compound
• • positive oxidation state- lost electrons
  • negative oxidation state- gained electrons
• rules for oxidation states

  • metals tend to lose electrons and non-metals gain electrons
  • transition metals- variable oxidation states
  • uncombined elements- 0
  • uncombined ions- charge on ion
• exceptions for oxidation states

  • H -> usually +1 becomes -1 in a metal hydride
  • O -> usually -2 becomes -1 in a peroxide
  • Cl -> usually -1 becomes positive value in compounds with O & F
• redox reactions involve both oxidation and reduction

  half equations show either the oxidation or reduction process
• half equations

  • assign oxidation states to identify oxidation/reduction
  • add electrons to equation (oxidation=RHS, reduction=LHS)
  • balance oxygens by adding water
  • balance hydrogen
• redox equations

  • multiply to balance electrons
  • combine half equations
  • cancel electrons
  • combine product ions
• • reducing agent- loses electrons
  • oxidising agent- gains electrons