Final answer:
The periodic table helps predict the formulas of stable ionic compounds by indicating the likely ion charges of elements, which are used to balance charges and determine compound formulas.
Step-by-step explanation:
The periodic table is a valuable tool for predicting the formulas of stable ionic compounds. Main-group elements tend to form cations with a charge equal to their group number. For example, group 1 elements form 1+ ions and group 2 elements form 2+ ions. Conversely, nonmetals, often found on the right side of the table, tend to form anions with a negative charge. Knowing an element's group number allows us to determine its likely ion charge and contribute to predicting compound formulas. Alkali metals form ions with a +1 charge, while alkaline earth metals form ions with a +2 charge and halogens form ions with a -1 charge. This information helps in determining formulas for simple ionic compounds by combining the cations and anions in such a way that the total charges balance to zero, providing the formula for a stable ionic compound.