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The diatomic element.

The prefix “mono-” is never used for the first element, and only used for the second element if ambiguity exists in the naming. A few examples for using the prefix “mono-” on the second element are:

● carbon monoxide

● dinitrogen monoxide

● nitrogen monoxide

Note: If the final vowel in a prefix is “a” or “o” it is dropped before the vowel in a stem name, for ease of pronunciation.

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Experiment Naming Ionic and Molecular Compounds

Converting a Molecular Compound Formula to a Name

Example 1: Writing a Nonmetal + Nonmetal Name: P2S5 1. Read the formula and look at the subscripts.

P2S5

Note that P and S are nonmetals, which can be determined by referencing a periodic table like the one in Figure 1.

2. Write the name of the first element with the correct Greek prefix.

P2 = diphosphorus

3. Write the root name of the second element with the suffix “-ide.”

S = sulfur = sulfide

4. Write the correct Greek prefix of the second element.

S5 = pentasulfide

5. Write the name of the molecular compound.

P2S5 = diphosphorus pentasulfide

Example 2: Writing a Nonmetal + Nonmetal Name: CO

1. Read the formula and look at the subscripts.

CO

2. Write the name of the first element with the correct Greek prefix. If the 1st element has the prefix “mono”, it is dropped.

C = carbon (NOT monocarbon)

3. Write the root name of the second element with the suffix “-ide.”

O = oxygen = oxide