Writing Ionic Formulas

• The formula for sodium chloride (NaCl) is Na+ Cl-
• (aq) means that the substance is dissolved in water.
• The formula for calcium carbonate (CaCO3) is Ca2+ CO32-
• Ionic compounds


  Compounds made up of metals and nonmetals
• Ionic compounds


  • Atoms in the compound have a charge
  • Charges must balance in the overall compound
• Steps to write chemical formulas for ionic compounds

  1. Find elements on periodic table

  2. Determine charges of elements

  3. Balance charges by adding more atoms

  4. Write chemical formula showing number of each atom
• Lithium


  Element with +1 charge
• Oxide


  Oxygen with a charge
• Metal and nonmetal


  Indicates an ionic compound
• Nitride


  Nitrogen with a charge
• Chloride


  Chlorine with a charge
• Charges must balance in an ionic compound
• Balancing charges in Lithium Oxide


  1. Start with Li+1 and O2-

  2. Add second Li+1 to balance 2- charge

  3. Write formula as Li2O
• Balancing charges in Potassium Nitride


  1. Start with K+1 and N3-

  2. Add two more K+1 to balance 3- charge

  3. Write formula as K3N
• Balancing charges in Sodium Chloride

  Na+1 and Cl-1 charges balance, so formula is NaCl
• Balancing charges in Aluminum Oxide

  1. Start with Al3+ and O2-

  2. Add second Al3+ to get 6+ charge

  3. Add third O2- to get 6- charge

  4. Write formula as Al2O3
• Mistakes to avoid when writing ionic compound formulas:
• 1. Don't add a 1 after an element (e.g. LiO1 is wrong, write Li2O)
• 1. Remove charges when writing final formula (e.g. don't write Li+2O2-)
• To write the formula for magnesium sulfate, first identify the cation (Mg2+) and then find the anion (SO4^2-) using the suffix -ite (-1) or -ate (-2). The subscript "2" indicates that there are two Mg atoms per one SO4 molecule.
• The formula for magnesium sulfate (MgSO4) is Mg2+ SO42-
• In the case of calcium phosphate, the prefix "hypo" (-1) is used instead of "-ite". This indicates that only one Ca atom is present per PO43- molecule.
• The formula for potassium nitrate (KNO3) is K+ NO3-
• The formula for magnesium sulfate is MgSO4.
• The formula for aluminum oxide is Al2O3.
• In aluminum hydroxide, the cation is Al3+ and the anion is OH-. Balance the charges by adding more Al3+ and OH- until they cancel out.
• When writing ionic formulas, it is important to remove any charges from the final formula.
• When writing ionic formulas, it is important to remember that all elements must be represented as either positive or negative ions.
• When balancing charges in aluminum oxide, start by identifying the charges on the elements involved. In this case, we have Al3+ and O2-. To balance the charges, we need to make sure they cancel out. We can do this by adding more positive charges to the left side and negative charges to the right side until both sides have equal charges.
• When writing the formula for calcium phosphate, we need to remove the charge from both the cation and anion since they have already been accounted for in the subscripts.
• Calcium chloride has a balanced formula of CaCl2.
• When balancing charges in calcium chloride, start by identifying the cations (Ca2+) and anions (Cl-), then balance the positive and negative charges until they cancel out.
• Ions can be represented by their symbols with appropriate superscripts indicating their charges.