Periodic Table of Elements

Steps to writing chemical formulas

  • 1. Write the symbols

    • Most chemical compounds have two names. The first name is the cation (positive ion) and the second name is the anion (negative ion).
    In a binary compound, the first name will be a metal ion. The second name will be a nonmetal ion.
    In a ternary compound, the first name will be a metal ion with the exception of ammonium. The second name will almost always be a polyatomic ion.
    Examples:

    Binary Ionic Compounds:
    Sodium Chloride: Sodium is Na and Chloride is Cl
    Magnesium Nitride: Magnesium is Mg and Nitride is N
    Ternary Ionic Compounds:
    Barium Phosphate: Barium is Ba and Phosphate is PO4
    Ammonium Carbonate: Ammonium is NH4 and Carbonate is CO3

  • 2. Determine the valence or charge of each symbol and write it as a superscript.

    • Examples:

    Binary Ionic Compounds:
    Sodium Chloride: Na+1, Cl-1
    Magnesium Nitride: Mg+2, N-3
    Ternary Ionic Compounds:
    Barium Phosphate: Ba+2, PO4-3
    Ammonium Carbonate: NH4+1, Carbonate is CO3-2

  • 3. Determine the common multiple of the charges and balance the total positive and negative charge on the cation and anion.

    • Examples:

    Binary Ionic Compounds:
    Sodium Chloride: Since each sodium is +1 and each chloride is -1 then it will take one Na+ to balance one chloride with a -1.
    Magnesium Nitride: Since each magnesium is +2 and each nitride is -3 then it will take three Mg+2 to balance two nitrides with -3.
    Ternary Ionic Compounds:
    Barium Phosphate: Since each barium is +2 and each phosphate is -3 then it will take three Ba+2 to balance two phosphates with -3.
    Ammonium Carbonate: Since each ammonium is +1 and each carbonate is -2 then it will take two NH4+1 to balance one carbonate with -2.

  • 4. The number of units of the cation and anion determined in step 3 above, those become the subscripts which are placed right after the respective symbol.
    Use parenthesis () incase of polyatomic ions.

    • Examples:

    Binary Ionic Compounds:
    Sodium Chloride: NaCl
    Magnesium Nitride: Mg3N2.
    Ternary Ionic Compounds:
    Barium Phosphate: Ba3(PO4)2
    Ammonium Carbonate: (NH4)2CO3