what is valency?
what is chemical formula?
how can it be applied
The combining power or the combining capacity of an atom or an element is called its valency. The number of atoms of other elements with which one atom of an element combines is decided by the valency of that element. In AlCl3, the valency of Al is 3 and it combines with three atoms of Al.
Chemical formula is an expression which is used to denote the number and types of elements that are present in one molecule of a compound. In other words, it is a symbolic representation of a chemical compound using only chemical symbols for elements and numbers to denote the relative ratios in which they are present. For example the chemical formula for water is H2O, while that for common salt (sodium chloride) is NaCl.
The chemical formula is formulated from the knowledge of symbols that are used to denote the chemical elements and their valencies. For example consider Sodium chloride. The symbol of sodium is Na and its valency is 1. Similarly the symbol of chlorine is chlorine is Cl and its valency is 1. This means that one sodium ion will combine with one chloride ion. So the chemical formula of sodium chloride is NaCl.
Similarly consider calcium chloride. The symbol for calcium is Ca and its valency is 2. Similarly the symbol of chlorine is chlorine is Cl and its valency is 1. This means that one calcium ion will combine with two chloride ions. So the chemical formula for Calcium chloride will be CaCl2.