Stock Names for Covalent Compounds

The second method of naming covalent compounds is to use Stock names.

Just as we use stock names for ionic compounds that involve transition metals that make more than one kind of ion, we also can use stock names for covalent compounds. Let's look at an example with an ionic compound and compare it to an example of a covalent compound.

Note: When we deal with covalent compounds we are not dealing with ions. However, using the stock name requires that we think about the oxidation numbers of the elements. An oxidation number is similar to - but not exactly the same as - an ion charge. We will talk about oxidation number in CH 105/122; for this lesson do not concern yourself about the difference between them.

name	titanium (IV) oxide	sulfur(IV) oxide
ions/oxidation number involved	Ti⁴⁺, O^2-	S⁴⁺, O^2-
formula	TiO₂	SO₂

Just as in ionic compounds, we only use the Roman numerals for the first element in the covalent compound. The oxidation number of the second nonmetallic element is determined by its place on the periodic table.

You can look in your workbook at ex. 13 for another example comparing the stock name for an ionic compound and a covalent compound.

Practice

Now, name or write the formula for the compounds in exercise 14 using the Stock method. The correct answers follow.

Answers

a) CO₂ is named carbon(IV) oxide. (Oxygen is the second element in the formula, so based on its position in Group VIA it is assigned an oxidation number of 2-. Since we have one carbon atom for two oxygen atoms, the carbon must have an oxidation number of 4+.)

b) N₂O₄ is named nitrogen(IV) oxide. (Again oxygen has an oxidation number of 2-; with a ratio of 2:4, the nitrogen must have an oxidation number of 4+.)

c) carbon(IV) fluoride has the formula of CF₄. (The Stock name tells us that C has a 4+ oxidation number. Fluorine is in Group VIIA, so its oxidation number is 1-. We need 4 fluorine atoms for every one carbon atom.)