Writing Formulas and Naming Compounds

Binary Compound This is a compound that is composed of two elements.

In order to write formulas for compounds, you need to know the oxidation number. The oxidation number tells you how many electrons have been gained, lost or shared. For ionic compounds, this is the same as the charge on the ion.

Compounds are neutral This is because the positive and negative ions must balance. For example, sodium chloride is made up of a sodium ion with a 1+ charge and a chloride ion with a 1- charge. This makes a neutral ion.

But what if an ion has a 2+ charge? Let’s take a look at the compound calcium fluoride. Calcium has a 2+ charge and fluorine has a 1- charge. How can this balance?

Let’s look at aluminum oxide: 1. Find the oxidation numbers. 2. Find the least common multiple to balance the charge in the compound. 3. Write the compound with the correct subscripts.

Aluminum oxide

Steps for writing formulas (p. 617 in book)

Steps for naming formulas 1. Write the name of the positive ion. 2. Determine the oxidation number. 3. Write the root name of the negative ion. (Ex. Chlor-) 4. to the root. Ex. - NaCAdd – ide l is Sodium chloride

Polyatomic ions