Ionic compounds have a set formula, based on the charges of the ions they are made from. For example, calcium chloride is CaCl2
This is the case because the calcium ion has a charge of 2+ and each fo the chloride ions have a charge of 1-. Overall, this means that the two positive charges and the two negative charges cancel each other out.
A good way of laying this out on paper is by using an ionic equation to show the formation of the ionic compound from its ions:
This is the case because the calcium ion has a charge of 2+ and each fo the chloride ions have a charge of 1-. Overall, this means that the two positive charges and the two negative charges cancel each other out.
A good way of laying this out on paper is by using an ionic equation to show the formation of the ionic compound from its ions:
Ca2+ + Cl- --> ?
So if we left the above equation as it is, we would get CaCl+ as only one of the positive charges on the calcium ion is cancelled by the negative charge on the chloride.
However, if we were to introduce a second chloride ion in the formula, then the negative charge it has would cancel the second negative charge on the calcium ion:
Ca2+ + 2Cl- --> CaCl2
And that's it - that's why ionic substances have the formula that they do. I would strongly recommend that you get familiar with the list of ions below, as in the new GCSE's you don't get them given to you on a data sheet as previous years did.
