Summary

Compounds fall into two large groups: molecular, in which the smallest unit of the compound is the moleucle, and ionic. Ionic compounds are formed by the union of ions in a ratio such that the compound and it formula have no net charge. Each compound has a systematic name that identifies its composition. Many compounds also have common names. Compounds are given systematic names based on certain rules, many of which depend on the oxidation numbers of the elements in the compound. Another set of rules is used to assign oxidation numbers.

The formula of a compound states which elements and how many atoms of each are present in the smallest unit of the compound. It also represents the mole ratio between the elements in the compound. The formula weight of a compound can be calculated from the formula and the atomic weights of elements present in the compound. The formula weight in grams is the mass of one mole of the compound. Using formula weights, the percent composition of a compound can be calculated.

If the percent composition of a compound is known, its empirical formula can be calculated. If both the olecular weight and the perecent composition of a compound are known, the molecular formula of the compound can be calculated. Several compounds may have the same empirical formula but different molecular formulas.