Naming Ionic formulas

• Naming/writing Ionic formulas


  1. Write down the name of the metal

  2. Write down the name of the nonmetal, changing the ending of the word to "-ide"
• Magnesium astatide


  Compound name
• Sodium phosphide


  Compound name
• Iron oxide


  Compound name
• Calcium sulphide


  Compound name
• Potassium nitride


  Compound name
• Strontium iodide


  Compound name
• Compounds formed by metal and non-metal elements


  • iron sulfide
  • magnesium nitride
  • sodium chloride
  • tin oxide
  • aluminium bromide
  • nickel iodide
  • zinc sulfide
  • lithium nitride
• Elements


  • sulfur
  • nitrogen
  • chlorine
  • oxygen
  • bromine
  • iron
  • magnesium
  • sodium
  • tin
  • aluminium
  • nickel
  • zinc
  • lithium
• Naming compounds containing oxygen


  1. Write down the name of the metal

  2. Write down the name of the non-metal, changing the ending to "-ate"
• A compound contains atoms from different elements that are chemically joined together
• A compound always contains a particular amount of each element. It has a fixed composition
• Compound names can get quite long and complicated, so the symbols of the elements are used as a shorthand
• The symbols of the elements in a compound are combined to give the formula of the compound
• How to write the formula of an ionic compound


  1. Write down the symbol for each element – the metal is always written first

  2. Calculate the charge for each type of ion

  3. Balance the number of ions so that the positive and negative charges are balanced and equal zero. This gives the ratio of ions

  4. Use the ratio to write down the formula of the ionic compound
• Formula of a compound

  Uses chemical symbols and numbers to show the ratio of atoms of each element present
• Oxidation number


  Can be referred to as a superscript or as a Roman numeral
• Roman numerals are used when writing the name of compounds to specify the oxidation number of the metal
• There is only 1 possible oxidation state for some metals, so no Roman numerals are used
• Polyatomic ionic compounds


  • Roman numerals are used to indicate the oxidation state of the metal
  • The endings for the polyatomic ions can be "-ide", "-ate" or "-ite" depending on the polyatomic ion
• The endings for polyatomic ions can provide information on how many oxygens are in the polyatomic ion
• Naming Polyatomic Ionic Compounds


  1. Identify the formula using criss-cross method

  2. Name the metal (cation) first. If it's a transitional metal determine the charge and assign the Roman numeral that's equivalent to the charge

  3. Name the polyatomic ion using its normal name
• Common Polyatomic Ions


  • Nitrate (NO3-)
  • Carbonate (CO3 2-)
  • Hydroxide (OH-)
  • Phosphate (PO4 3-)
  • Ammonium (NH4+)
  • Sulphate (SO4 2-)
• Writing Chemical Formulae – The Crisscross method

  1. Determine the oxidation number of each element or polyatomic

  2. This number becomes the subscript of the other ion (w/o the charge, i.e. crisscross)

  3. An Oxidation number of 1 is not used as a subscript

  4. Subscripts must be reduced to the smallest whole number ratio
• Examples of the crisscross method


  • Iron (II) bromide: FeBr2
  • Chromium (III) oxide: Cr2O3
  • Calcium sulfide: CaS
  • Ammonium phosphate: (NH4)3PO4
• Assigning Oxidation #


  1. The total charge on any compound or molecule is always equals to ZERO

  2. To determine unknown oxidation #s, let the unknown oxidation # be x, add up the oxidation #s of the metal and non-metal ion and set them equal to ZERO
• Name These


  • Chromium (IV) oxide
  • Lead (IV) oxide
  • Potassium dichromate (VI)
  • Tin (IV) oxide
  • Potassium manganate (VII)
• Brackets are used to separate the formula of polyatomic ions and the subscript after crossing the charges
• Charges of transition metals are written in roman numerals in brackets after the metal ion
• Subscripts must be reduced to the smallest whole number ratio