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Binary Ionic Compounds


    To learn how to interpret and write binary ionic compounds, simply follow the rules below.

   The first element in the name is the metal. For example: use the name Sodium to name the metal NaCl. Use the name Calcium to name the metal CaCl2.

   The second element, which is the non-metal, is named as an ion. In other words: the suffix "-ide" is attached to the name. For example: NaCl is called Sodium Chloride. This allows us to name the non-metal NaCl.

   Be sure to put the parts of the name together. For example: NaCl is called Sodium Chloride, and CaCl2 is called Calcium Chloride. 

Remember: names of ionic compounds do not contain the prefixes "mono, di, tri, etc..."


Writing Formulas for Binary Ionic Compounds



Step 
1

Write the unbalanced formula, placing the metal ion first.

Example: Magnesium Fluoride

Mg = Magnesium
F = Fluorine

So: MgF

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Step 2
Write the charge of the ion on the top of the appropriate symbol. Recall that metal ions from Group 1 have a charge of +1. Metal Ions from Group 2 have a charge of 2+. Halogen ions have a charge of -1. Oxide ions have a charge of -2.

Example: Magnesium Fluoride

Mg2+ F-1


Step 3
Cross over the numerical value of each charge and write this number as the subscript for the other ion in the compound. Do not include negative or positive signs, and do not include the subscript #1 in the formula.

Example: Magnesium Fluoride

Mg+2  F-1

MgF2

We give the 2 to the F and the -1 to the Mg, but we do not write "-1 or 1" because there is an understanding that when an element is written as such, the 1 is present (just not visibly written).


Remember: if the numbers on each element are not equal, that is, if they are +2 and -3, or +1 and -2, take them for a walk! They will switch sides. (Be+2  N-3 becomes Be3N2, while Na+1  S-2 becomes Na2S).