Naming Compounds and Molecules

Before naming a compound, you have to know what kind it is….

1. Ionic Compounds without a transition metal Ionic compounds are formed when a metal gives its electrons to a non-metal. So, if the compound contains a metal, it is ionic. (The rules are different for transition metals. We’ll get to that later.)

For compounds without transition metals, these rules apply:

The metal ion's name does not change The non-metal's name ends in ide.For example: AlCl3 = aluminum chloride

Na2S = sodium sulfide

K2O = potassium oxide

MgH2 = magnesium hydride

(The subscripts do not affect the way we name them.)

Sometimes, you will be asked to look at the name for a compound and write the formula.

• For example, calcium phosphide:• • Using the Periodic Table, you have to find the charges for

calcium and phosphorus, which are +2 and -3, respectively. (Calcium loses two electrons to gain stability and phosphorus needs three more electrons.)

Ca+2 and P-3

To balance this and get a sum of zero, we need three Ca+2 ions and two P-3 for a total of 3(2)+ 2(-3) = 0. So the answer is Ca3P2.

Do you already feel like this guy?Sorry.. there’s more!

Polyatomic Ions

These are ions consisting of two or more elements with one overall charge.

Naming compounds with polyatomic ions

• 1. Write the name of the positive ion (cation).• 2. Find the name of the polyatomic ion. • 3. Combine the two names.

• Ex. – K2SO4 is called potassium sulfate

Writing formulas for polyatomic ions

It’s not that difficult! Just follow the rules for binary compounds with one addition: use parentheses around the polyatomic ion before adding the subscript.

Ex. – Ba(ClO3)2 – this is barium chlorate

Hydrates

Compounds with chemically attached water are called hydrates. A compound such as this is said to be anhydrous.

CaSO4 2H2O is called calcium sulfate dihydrate.

Naming covalent compounds

Can you use the prefixes to name the following compounds?

• N2O

• NO

• NO2

• N2O5