When naming a molecular compound, such as CO, would I write it as mono carbon monoxide or carbon monoxide? My textbook has the rule written as prefix+1st element prefix+2nd element, but I am not sure if the mono applies to the carbon or not.

carbon monoxide

This makes the difference clear between carbon monoxide CO and carbon dioxide CO2
You do not need to say
mono carbon monoxide or mono carbon dioxide because they are both one carbon and there is no confusion.

When naming a molecular compound such as CO, the use of the prefix "mono" is generally not required for the first element. In this case, CO is named as carbon monoxide. The "mono" prefix is used when there is more than one atom of the second or the third element in the compound. For example, if you have CO2, it would be named as carbon dioxide, with the "di" prefix indicating two oxygen atoms. But when there is only one atom of the first element, like in CO, there is no need for the "mono" prefix.

When naming a molecular compound, such as CO (carbon monoxide), you would write it simply as "carbon monoxide" and not "mono carbon monoxide." The use of the prefix "mono" is not necessary in this case.

The rule you mentioned, "prefix + 1st element prefix + 2nd element," is a commonly accepted system for naming molecular compounds. The prefixes used in this system indicate the number of atoms of each element present in the compound. However, there are exceptions to this rule.

Specifically, the prefix "mono" is only used when there is only one atom of the first element in the compound. In the case of carbon monoxide (CO), there is already just one carbon atom present, so we don't need to use the prefix "mono." If there were more than one carbon atom, then the appropriate prefix would be used. For example, if you had C2O, you would name it "dicarbon monoxide."

In summary, for molecular compounds like CO, you would typically name them by stating the name of the first element, followed by the name of the second element, without using the prefix "mono" unless it is necessary.