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

Formula is the symbolic representation of compounds. If we know the symbols, radicals and valencies of different elements, we can write the formula of any compound easily.
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 aluminium chloride would be CaCl₂.