Question

Using the example of calcium chloride explain how the formulae of compounds are derived (given that the valency of calcium is 2 and that of chlorine is 1).

Answer 1

The steps involved in writing the formula for a compound are as follows:
1. Note down the symbols of the elements or their radicals. Then note down the valencies as superscript on the symbols of the elements.
2. If there is a common factor in the valencies, then divide it to a simple one.
3. Exchange the valencies and write them as subscripts.
[Note: If the radicals contain more than 2 atoms, they will be written in brackets and the exchanged valence number is written as subscript.]

Let's use the above steps for writing the formula for calcium chloride.
* The elements in calcium chloride are calcium and chlorine. The valency of calcium is 2 and chlorine is 1. Therefore, we write the symbols as Ca² and​ Cl¹.
* The common factor among the numbers 1 and 2 is nil.
* The valencies are exchanged and written as subscripts to the elements. Therefore, the formula of calcium chloride would be CaCl₂.