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Ionic compound formula

What are ionic compounds?

Ionic compounds are neutral compounds made up of positive cations and negative anions.Every ionic compound has discrete ionic units with a specific charge. An Ionic compound always contains equal amount of positive and negative charge. The chemical formula of an ionic compound represents its ionic units and cation to anion ratio.

Chemical formulas of ionic compounds are not complicated to write. Write the cation symbol followed by anion symbol. Then, find the lowest multiple of the ions to make the compound neutral.Ionic compounds consist of positively and negatively charged ions, but the overall compound and its formula are electrically neutral. In other words,

   Total Positive charge of cation = Total Negative charge of anion

Ionic compounds usually consist of a combination of metals and nonmetals.These are the guidelines to ensure uniformity in writing the ionic compound formula.

  1.    The cation is always placed before anion.
  2.    Polyatomic ion formula is always written as a unit.
  3.    Polyatomic ions are placed in parentheses with the following subscript to represent different ratios from 1:1.

Example 1

Identify which of the following substance are ionic.


To determine the ionic compound, look for Group 1 or Group 2 metals or Polyatomic ions.

In , the presence of strontium which is a Group 2 metal shows that strontium chloride is an ionic compound.  

In , Chlorine exists as a -1 anion but there are no cation in carbon tetrachloride, therefore  is not ionic.

Example 2

Determine the chemical formula of the ionic compound Calcium Chloride.


The names of cations and anions identify the chemical formulas along with changes of each ion.The charges indicate the ion ratio that needs to appear in the chemical formula.

Calcium chloride contains Ca+ of Group 2 and Cl- of Group 17. That’s the reason there must be two anions for every cation. Therefore, the chemical formula of calcium chloride is

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