Chemistry 2

Naming and Formulas for Ionic Compounds

  1. Ionic compounds are formed between oppositely charged ions usually consisting of a metal and one or more non-metals.
  2. An ion can be a single charged atom or a small group of atoms (molecule) with a charge.
  3. Binary Ionic Compounds (compounds composed of two single atom ions)
    1. Naming
      1. We can form ionic compounds from choosing a metal and a nonmetal, because they have a large difference in their electronegativity. This is best taught by example
      2. Sodium and chlorine form Sodium Chloride.
      3. Magnesium and oxygen form Magnesium Oxide.
      4. Calcium and sulfur form Calcium Sulfide.
      5. Binary ionic compounds are named by removing the end of the name from the nonmetal and adding -ide.
    2. Formula writing
      1. To write the correct formula you must know the charges present on each ion. To determine this you would look on the periodic table or your common ion sheet.
      2. The positive and negative charges must exactly balance each other in order to have the correct ratio of ions to form a neutral compound.
      3. Sodium can form a +1 charged ion and is written: Na+1
      4. Sulfur can form a -2 charged ion and is written: S-2
      5. The formula for Sodium Sulfide is Na2S
      6. Some other common ions that you should memorize: K+1, Ag+1,Mg+2, Zn+2, Al+3, Ca+2, O-2, Cl-1
      7. Click here to see how binary ionic compounds dissolve compared to molecular compounds.
      8. Try some examples below:
        Calcium Fluoride = Potassium Chloride =
        Lithium Oxide = Aluminum Sulfide =
  4. Polyatomic Ionic Compounds
    1. Sometimes a group of atoms can have a charge. This is called a poly atomic ion.
    2. Some common poly atomic ions which you should memorize are: nitrate NO3-1, sulfate SO4-2, carbonate CO3-2, bicarbonate (or hydrogen carbonate) HCO3-1, and hydroxide OH-1
    3. Notice that the names of these ions end in -ate.
    4. When you see a name ending in -ate it probably implies that it is a polyatomic ionic compound.
    5. The groups of atoms can be thought of as a single entity with a charge, just like a single atom can have a charge. For example, Sodium Nitrate needs one +1 sodium ion to neutralize one -1 nitrate ion, so the formula is NaNO3.
    6. If you need more than one polyatomic ion then you put parenthesis around it in the formula. For example, Calcium Nitrate needs one +2 calcium ion to neutralize two -1 nitrate ions, so the formula is Ca(NO3)2.
    7. Click here to see how polyatomic ionic compounds dissolve.
    8. Try some examples below:
      Sodium Sulfate = Zinc Phosphate =
      Barium Hydroxide = Ammonium Sulfate =
  5. Ions with multiple charges
    1. Some atoms can commonly form 2 or 3 different charges. These atoms are typically transition elements.
    2. Copper, for example, usually forms +1 or +2 charged ions.
    3. This can cause problems if a compound is named Copper Oxide. This could have the formula CuO or Cu2O depending on the charge of the copper atom.
    4. To clear up this ambiguity we can name the ions by specifically adding on a number to their name. Cu+1 is Copper(I) and Cu+2 is Copper(II). So the names of the copper compounds listed above are Copper(II)Oxide for CuO and Copper(I)Oxide for Cu2O.
    5. Try some examples below:
      Iron(II)Oxide = =CuSO4
      Iron(III)Oxide = = Cr(NO3)3