Naming Molecular Compounds - Online Tutor, Practice Problems & Exam Prep

Molecular compounds, also known as covalent compounds, consist of nonmetals bonded together and require numerical prefixes for naming due to their ability to combine in various proportions. The naming process involves three steps: the first nonmetal is named normally (excluding the prefix 'mono'), the second nonmetal retains its base name but ends with 'ide' and can use any numerical prefix. When the prefix ends with 'a' and is followed by an 'o', the 'a' is dropped to avoid awkward pronunciation. For example, 'tetroxide' becomes 'tetraoxide' when adhering to this rule. Understanding the correct application of these rules is crucial for accurately naming covalent compounds.

Naming Molecular Compounds

Here we're going to learn how to name molecular compounds. First off, molecular compounds are the same thing as covalent compounds. And remember that covalent compounds are compounds containing only nonmetals bonded together. We're going to say here that they use numerical prefixes. Now, numerical prefixes are always required because these compounds can combine in different proportions, and our numerical prefixes go from mono all the way to deca, so mono one.

Some of them are pretty familiar to us. Pentagon five sides, so penta is five, hexagon is 6 sides, so hexa is 6. Some may not be as common for us, Hepta meaning 7 and nona meaning 9. Now how exactly do we go about naming these covalent or molecular compounds? Well, here we're going to say step one is that the first nonmetal is named normally and uses all numerical prefixes except for mono. It does not use mono.

The second nonmetal keeps its base name, uses any numerical prefix, and has its ending changed to ID. And then finally what we need to realize with this is when naming if the letter A of the numerical prefix is next to a letter O, we must just drop the letter A. So for example we have tertroxide. Tetroxide means we have oxygen because the base name is OX and there are 4 oxygens, Tetra meaning 4. But we have an A and an O next to each other, and when we have an A and an O next to each other, we just drop the A, so this becomes tertroxide.

Now that we know what molecular or covalent compounds are, and we know the rules for them, let's look at some questions and apply what we just learned.

Naming Molecular Compounds Example 1

In this example question it says write the formula for each of the following compounds. So for the first one we have is disulfir monochloride. So dye means 2 to sulfurs so that's S2 and then mono chloride. Chloride is the base name of chlorine and model means we have one of it. So this would be S2Cl.

For the next one we have Tetraphosphorus pentaclenide. Alright, so Tetra means 44 phosphoruses, so P4 penta means 5 and Celine is the base name of selenium which is Se and they're being 5 of it would be P4Se5.

Then finally we have dibromo heptoxide, so dye means 2 to bromines so Br2 and we have Hept oxides. So Hept comes from Hepta which means 7 and then AUX means oxygen. So there are 7 oxygen's. So Dibromo heptoxide is Br2O7.

So just remember the first non metal keeps its name as normal uses all numerical prefixes except for mono. The 2nd nonmetal uses any numerical prefixes, but has its ending changed to ID.

Give the systematic name for the following compound:SeF₆

• A. selenium fluoride
• B. selenium hexafluoride
• C. monoselenium hexafluoride
• D. monoselenium fluoride
• E. selenium fluorite

Give the systematic name for the following compound:IO₅

• A. iodine oxide
• B. monoiodine oxide
• C. iodine pentoxide
• D. iodide pentoxide
• E. monoiodide pentoxide

Give the systematic name for the following compound:N₂S₄

• A. nitrogen tetrasulfide
• B. dinitrogen tetrasulfide
• C. dinitrogen sulfide
• D. nitrogen sulfide
• E. nitrogen sulfite

Here’s what students ask on this topic:

How do you name covalent compounds?

Naming covalent compounds involves a few simple rules. First, the name of the compound is constructed by using the full name of the first element (or a modified version if it's a polyatomic group), followed by the name of the second element with an "-ide" suffix. For example, CO is carbon monoxide.

If there are multiple atoms of an element, you use prefixes to indicate the number of atoms. These prefixes are: mono- (1), di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6), hepta- (7), octa- (8), nona- (9), and deca- (10). For instance, $N_2{O}_5$ is dinitrogen pentoxide. Note that the prefix mono- is often omitted for the first element, so CO is carbon monoxide, not monocarbon monoxide.

Remember that these rules apply to binary covalent compounds, which are compounds composed of two different nonmetal elements. When naming compounds with more than two elements, such as those containing polyatomic ions, the naming can become more complex and often involves memorizing the names of common polyatomic ions.

How is naming ionic and covalent compounds different?

When naming ionic compounds, which consist of metals and nonmetals, you first name the cation (metal) and then the anion (nonmetal). For the anion, you use the root of the element's name and add the suffix '-ide.' For example, NaCl is named sodium chloride. If the ionic compound contains a polyatomic ion (a charged group of covalently bonded atoms), you use the name of that ion directly, such as in sodium sulfate (${\mathrm{Na}}_2{\mathrm{SO}}_4$).

In contrast, when naming covalent compounds, which are formed between nonmetals, you use prefixes to denote the number of atoms of each element present in the compound (mono-, di-, tri-, etc.). The first element retains its name, and the second element's name is modified to end with '-ide' just like in ionic compounds. However, the prefix 'mono-' is typically omitted for the first element. For example, ${\mathrm{CO}}_2$ is carbon dioxide, and $P_4{O}_{10}$ is tetraphosphorus decoxide. Remember that these naming conventions do not apply to compounds with transition metals, which often require Roman numerals to indicate the charge on the cation, such as in copper(II) oxide for ${\mathrm{Cu}}_{\mathrm{O}}$.

What are the rules for naming covalent compounds?

In covalent compounds, atoms share electrons to achieve stability. When naming these compounds, there are specific rules to follow:

1. The element with the lower group number in the periodic table (or the one that is furthest left if both are in the same group) is written first. If both elements are in the same group, the one with the higher period number is named first.
2. The second element is named by taking its root and adding the suffix "-ide."
3. Prefixes are used to denote the number of atoms of each element in the compound (mono- for one, di- for two, tri- for three, tetra- for four, penta- for five, etc.). The prefix "mono-" is often omitted for the first element.
4. If the prefix ends in a vowel and the element name starts with a vowel, the final vowel of the prefix is often dropped to make the name easier to pronounce.

For example, $\mathrm{CO}$ is carbon monoxide, not monocarbon monoxide, and ${\mathrm{CO}}_2$ is carbon dioxide.