Assignment 4 - Writing Formulas

Anions and cations always combine to form neutral compounds.

formula unit - group of atoms or ions explicitly symbolized in the formula

ionic compounds - ionic bonds hold the atoms together.

molecular compounds - covalent bonds hold the atoms together.

chemical formula - a notation to indicate the type and number of atoms that make up a molecule or the smallest ratio of atoms/ions in an ionic compound

Rules for writing formulas for ionic compounds

- Each atom present is represented by its element symbol.

- The number of each type of atom is indicated by a subscript written to the right of the element symbol.

- The subscript 1 is not written.

- Formulas for ionic compounds are written with the smallest subscripts so that the overall charge is 0. The cation is written first.

- Charges are not written.

- The formula does not depict the structure of the ionic compound but only the simplest ratio of cations and anions.

- Cations or anions can be monatomic or polyatomic. The atoms in a polyatomic ion are bonded by covalent bonds.

- Polyatomic ions are written in parentheses if the subscript is 2 or higher.

- The formula is referred to as a formula unit to distinguish it from a molecule.

Do the following assignments on page 121f: # 11, 12, 15, 16

Chemical Formulas and Nomenclature - Quiz on __________