Determine the location of the atoms on the Periodic Table. The metals are located on the right side of the Periodic Table and the nonmetals are located on the left side of the table, except for hydrogen, H. If a metal and a nonmetal form a bond, then the compound will be ionic, such as KBr. If two nonmetals form a bond, then the compound will be covalent, such as CH4.
Know which elements form diatomic molecules. Some atoms bind to another atom of the same type in order to form a bond. Examples of such atoms are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine.
Determine the charges of each of the atoms. Elements in group 1 of the Periodic Table typically have a charge of +1, those in group 2 typically have a charge of +2, group 17 typically have a charge of -1, and oxygen typically has a charge of -2. Hydrogen has a +1 charge when combined with nonmetals and a -1 when combines with metals. For example, K has a +1 charge and Br has a -1 charge, so the compound formed is KBr, with subscripts of -1, which are omitted.