Naming Binary Molecular Compounds: Study with Video Lessons, Practice Problems & Examples

Binary molecular compounds consist of two different nonmetals, such as water (H₂O) and nitrogen oxides (NO). Naming these compounds involves using numerical prefixes: mono (1), di (2), tri (3), tetra (4), penta (5), hexa (6), hepta (7), octa (8), nona (9), and deca (10). The first nonmetal is named normally without "mono," while the second takes the base name, a prefix, and ends in "ide." If a prefix ending in "a" is adjacent to "o," the "a" is dropped, as in "tetroxide" for four oxygens.

Naming Binary Molecular Compounds Concept 1

Now, binary molecular compounds are molecular compounds that contain two different elements together. These elements being nonmetals. For example, we have water, and we have nitrogen with oxygen. Here we have hydrogen with oxygen. That's two different elements together. Here we have nitrogen with oxygen. Again, two different nonmetals together. Now, we're going to say that these molecular compounds utilize numerical prefixes, and that's because these numerical prefixes are always required because these compounds can combine in different proportions. Now with numerical prefixes, we have mono, which is 1, di, which is 2, tri, which is 3, tetra, which is 4, penta, which is 5, hexa is 6, hepta is 7, octa is 8, nona, a little weird sounding, is 9, and then, of course, deca is 10. So, just remember when we talk about binary molecular compounds, that's molecular compounds, covalent compounds that contain two different nonmetals together.

Naming Binary Molecular Compounds Concept 2

So when it comes to naming binary molecular compounds, these are the rules you need to keep in mind. Step 1, we're going to say the first nonmetal is named normally and uses all numerical prefixes except for mono. So it doesn't ever use mono. The second nonmetal keeps its base name, uses any numerical prefix, and has its ending changed to -ide. And when naming, if the letter "a" of the numerical prefix is next to a letter "o", we can just drop the letter "a". For example, we say tetraoxide, meaning we have 4 oxygens within our molecular compound. Here "a" and "o" are next to each other and we're going to do what it says. We're going to drop the letter "a". So tetraoxide would become tetroxide. Keep these steps or rules in mind when naming any type of binary molecular compound.

Naming Binary 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 disulfur monochloride. So "di" means 2, so there are 2 sulfurs. So that's S₂, and then "mono" indicates there is one of it, so for chloride (chlor being the base name of chlorine), the formula becomes S₂Cl. For the next one, we have tetraphosphorus pentaselenide. Alright, "tetra" means 4, indicating 4 phosphoruses, so P₄. "Penta" means 5, and selen is the base name of selenium which is Se, so there being 5 of it would be Se₅, resulting in the formula P₄Se₅. Then finally, we have dibromoheptoxide. So "di" means 2, indicating 2 bromines, so Br₂, and we have heptoxide, where "hept" comes from "hepta", which means 7, and "ox" means oxygen, so there are 7 oxygens. So, dibromoheptoxide is Br₂O₇. So just remember, the first nonmetal keeps its name as normal, uses all numerical prefixes except for mono. The second nonmetal uses any numerical prefixes, but has its ending changed to "ide".

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:

What are binary molecular compounds and how are they different from ionic compounds?

Binary molecular compounds consist of two different nonmetals bonded together through covalent bonds, where electrons are shared between atoms. Examples include water (H₂O) and nitrogen dioxide (NO₂). In contrast, ionic compounds are formed between metals and nonmetals, where electrons are transferred from the metal to the nonmetal, creating ions. An example of an ionic compound is sodium chloride (NaCl). The key difference lies in the type of bonding: covalent for molecular compounds and ionic for ionic compounds.

What are the rules for naming binary molecular compounds?

To name binary molecular compounds, follow these rules: 1) The first nonmetal is named normally and uses numerical prefixes except for 'mono'. 2) The second nonmetal keeps its base name, uses any numerical prefix, and ends in 'ide'. 3) If a prefix ending in 'a' is adjacent to 'o', the 'a' is dropped. For example, 'tetraoxide' becomes 'tetroxide'. Numerical prefixes include mono (1), di (2), tri (3), tetra (4), penta (5), hexa (6), hepta (7), octa (8), nona (9), and deca (10).

Why are numerical prefixes important in naming binary molecular compounds?

Numerical prefixes are crucial in naming binary molecular compounds because they indicate the number of atoms of each element in the compound. These compounds can combine in different proportions, leading to different compounds with distinct properties. For example, CO (carbon monoxide) and CO₂ (carbon dioxide) are different compounds with different properties. The prefixes help distinguish between these compounds by specifying the exact number of atoms involved.

How do you name a compound with the formula N₂O₄?

To name the compound N₂O₄, follow the naming rules for binary molecular compounds: 1) The first nonmetal (nitrogen) is named normally with the prefix 'di' for two atoms, becoming 'dinitrogen'. 2) The second nonmetal (oxygen) uses the base name 'oxide' with the prefix 'tetra' for four atoms, becoming 'tetraoxide'. Since 'a' and 'o' are adjacent, drop the 'a'. The name is 'dinitrogen tetroxide'.

What is the significance of dropping the 'a' in prefixes like 'tetra' when naming binary molecular compounds?

Dropping the 'a' in prefixes like 'tetra' when it is adjacent to 'o' in naming binary molecular compounds simplifies pronunciation and avoids awkward combinations of vowels. For example, 'tetraoxide' becomes 'tetroxide'. This rule helps maintain clarity and ease of communication in chemical nomenclature.