Stock Names of Covalent Compounds

Sometimes covalent compounds are named using stock names. This system works similarly to naming ionic compounds with stock names. Think about why we use stock names with ionic compounds; we use stock names when more than one compound can be formed with the same elements. That occurs when the metal is a transition metal that forms more than one ion.

Nonmetals often can combine to make more than one compound also - for example, carbon and oxygen can combine in a 1-to-1 ratio in CO or in a 1-to-2 ratio in CO₂. Using stock names is another way to distinguish between the possible compounds. Remember that with ionic compounds, the Roman numerals in a stock name indicated the charge on the metal ion. Covalent compounds do not contain ions, so how can we use a stock name? Since nonmetals have different electronegativities, the atoms are not sharing their electrons equally; one of the atoms in a polar bond will have a stronger pull for those shared electrons. One method for keeping track of the electrons in a compound is to assign an oxidation number to each element. We are not going to be concerned in this lesson about the specific differences between oxidation numbers and ion charges (we will revisit oxidation numbers in CH 105/122). For now, you can simplify the concept by thinking about oxidation numbers as "pseudo-charges". When we figure out the correct ratios for the elements we will deal with the oxidation numbers as if they are actual charges (even though we know that is not completely correct).

Let's look at an example of an ionic compound that has a stock name.

Stock name:	Ions present:
iron(II) oxide	Fe²⁺ and O²
Formula:	FeO

Now here's an example of a covalent compound with its stock name.

Stock name:	Oxidation states:
carbon(II) oxide	C²⁺ and O^2- (The Roman numeral tell us the oxidation number of the element directly in front of it, just like in ionic compounds. The oxidation number of the other element is determined by its position on the periodic table.
Formula:	CO

Try your hand at the following practice problems, also found in exercise 14 in your workbook.

Practice Problems

CO₂

N₂O₄

carbon(IV) fluoride

Answers:

CO₂ is carbon(IV) oxide. (Oxide should be O^-2 so with a ratio of 2 O to 1 C, the C should be C⁴⁺ )

N₂O₄ is nitrogen(IV) oxide. (Oxide is O^2- again so the nitrogen must be N⁴⁺ since the ratio is 2 O to 4 N.)

carbon(IV) fluoride is CF₄. (The Roman numeral shows that we have C⁴⁺ and F is F^1-, so they must be combined in a 1-to-4 ratio.)

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E-mail instructor: Eden Francis