3.3 - Oxidation Numbers

• Oxidation state


  shows total number f electrons removed or added to an element to get it to its present state
• increase in oxidation state

  element has lost electrons so has been Oxidised
• decrease in oxidation state

  element has gained electrons so has been reduced
• Oxidation numbers rules


  uncombined elements have an oxidation state of 0

  Oxidation state of a monoatomic ion is the same as its charge

  oxidation numbers of molecular ions added together = charge

  sum of oxidation numbers in neutral compounds is 0
• Oxidation state of group 1 metals

  always +1
• oxidation state of group 2 metals

  always +2
• oxidation state of Oxygen

  usually -2

  exept peroxides (O2)2- and with F
• Oxidation state of hydrogen

  usually + I

  exept hydride H-
• Oxidation state of fluorine

  always -1
• Oxidation state of chlorine

  usually -1

  exept with O and F
• roman numerals and oxidation state

  tells you the oxidation number when an element has multiple oxidation states or isn't in it's normal oxidation state
• ending of oxoacids

  -ic or -ous

  -ic is for acid where central atom has the higher oxidation number

  e.g: sulfuric acid (H2SO4), sulfurous acid (H2SO3)
• endings for salts of oxoacids

  -ate and -ite

  e.g: sulfate (SO4)2-, sulfite(SO3)2-
• what -ide ending shows

  a compound has just the two elements mentioned in the name

  the more electronegative element comes second