2. Chemical Formulas and Composition Stoichiometry

The word "stoichiometry" is derived from the Greek __, which means "first principle or element," and metron, which means to measure.

It describes the quantitative relationships among elements in compounds and among substances as they undergo chemical changes.

Different forms of the same element in the same physical state are called __.

There are no "molecules" of ionic substances, thus one should not refer to a "molecule of sodium chloride, NaCl." Instead, they are referred to as a __. It represents the smallest, whole-number ratios of ions that yield neutral representations of all substances (both ionic and non-ionic). Therefore, one __ of propane, C3H8, is the same as one molecule of C3H8.

It is defined as exactly 1/12 of the mass of an atom of a particular kind of carbon atom, called carbon-12.

The __ of a compound is the smallest, whole-number ratio of atoms present.