Chemical Formulas

4

These skills are usually tested on the SAT Subject Test in Chemistry. You
should be able to...

Recall and use the basic rules about ionic charges to write correct

formulas for ionic compounds. This includes writing formulas with

polyatomic ions.

Recall and use the basic rules about writing compounds for

covalent (molecular) compounds.

Name compounds (acids, bases, and salts) using the Stock system

and the prefix system, and write their formulas.

Calculate the formula mass of a compound and the percent

composition of each element.

Calculate the empirical formula when given the percent

composition of each element. When given the formula mass, you

should be able to find the true formula.

Write a simple balanced equation, indicating the phase (or state)

of the reactants and products.

This chapter will review and strengthen these skills. Be sure to do the
Practice Exercises at the end of the chapter.

NAMING AND WRITING CHEMICAL FORMULAS

With the knowledge you have about atomic structure, the significance of each
element’s placement in the periodic table, and the bonding of atoms in ionic and
covalent arrangements, you can now use this information to write appropriate
formulas and name the resulting products. Obviously, many compounds can result.
Some system of writing the names and formulas of these many combinations was
needed. The system explained in this text is an organized way of accomplishing
this. It uses three categories:

CATEGORY I—Binary ionic compounds where the metal present forms

only a single type of positively charged ion (cation)