Posted by Shijo. S.G on July 20, 2013, 11:37 a.m.
Valency is the combining capacity of an element. Valency can be used
to find out how many atoms of an element will combine with the other
element to form a chemical formula. For example, hydrogen has a valency
+1 and chlorine has a valency –1, so one atom of hydrogen combines with
one atom of chlorine to form hydrochloric acid (HCl). Oxygen has a
valency –2, so one atom of oxygen combines with two atoms of hydrogen to
form water molecule (H2O).