After that, any other elements appear in alphabetical order. S 2- P olyatomic Ions Ionic compounds also contain clusters of atoms with a net negative charge. Chlorine, bromine, and iodine each form four different oxyanions that are distinguished by prefixes and suffixes. These anions are named from the parent anion by adding hydrogen. For any metal that forms more than one stable cation, the charge is specified by using a Roman numeral in parentheses after the name of the metal.
Many ionic compounds have water molecules incorporated into their crystalline structures.
Such compounds are called hydrates . A structural formula not only gives the number of atoms in a molecule but also shows how the atoms are connected to one another. Atoms are held together by attractive forces called bonds. For now, understand that a chemical bond is formed between a pair of electrons shared between two atoms. In a structural formula, the bonds between atoms are represented by lines connecting the elemental symbols.