An atom of a pure element has an oxidation number of zero. For single atoms in an ion, their oxidation number is equal to their charge. Fluorine is always -1 in compounds. The oxidation number of a compound is equal to the sum of the oxidation numbers for each atom in the compound. Forming Ionic Compounds Knowing the oxidation number of a compound is very important when discussing ionic compounds.
Ionic compounds are combinations of positive and negative ions.
They are generally formed when nonmetals and metals bond. To determine which substance is formed, we must use the charges of the ions involved. In order to create a neutral charged molecule, you must combine the atoms in certain proportions. Scientists use subscripts to identify how many of each atom makes up the molecule. Knowledge of the charges of ions is crucial to knowing the formulas of the compounds formed.