Binary Molecular Compounds: Naming and Numerical Prefixes

Binary Molecular Compounds

Introduction to Binary Molecular Compounds

Binary molecular compounds are chemical compounds composed of exactly two different elements. These compounds are typically formed between nonmetals and are distinct from ionic compounds. Examples include H2O and NO.

• Binary molecular compounds contain two different elements.

• Numerical prefixes are always required in naming to indicate the number of atoms of each element present in the compound.

Numerical Prefixes for Binary Compounds

Numerical prefixes are used to specify the number of atoms of each element in a binary molecular compound. The table below lists the prefixes for numbers 1 through 10:

Number	Prefix
1	Mono
2	Di
3	Tri
4	Tetra
5	Penta
6	Hexa
7	Hepta
8	Octa
9	Nona
10	Deca

Rules for Naming Binary Molecular Compounds

Naming binary molecular compounds follows a systematic approach to ensure clarity and consistency:

1. Step 1: The first nonmetal is named normally and uses a numerical prefix except for "mono" (which is typically omitted for the first element).

2. Step 2: The second nonmetal keeps its base name, uses any numerical prefix, and has its ending changed to -ide.

3. Additional info: When naming, if the letter "a" of the numerical prefix is next to a vowel in the element name, it is often dropped for ease of pronunciation. For example, "tetraoxide" becomes "tetroxide".

Examples of Naming Binary Molecular Compounds

• Disulfur monochloride: S2Cl

• Tetraphosphorus pentaeselene: P4Se5

• Dibromine heptoxide: Br2O7

Practice Problems

Apply the rules for naming binary molecular compounds to the following examples:

• SeF6: Hexafluoride is the prefix for six fluorine atoms. The compound is Selenium hexafluoride.

• IO: Monoxide is the prefix for one oxygen atom. The compound is Iodine monoxide.

• N2S4: Tetrasulfide is the prefix for four sulfur atoms. The compound is Dinitrogen tetrasulfide.

Key Terms and Definitions

• Binary molecular compound: A compound composed of two different nonmetal elements.

• Numerical prefix: A prefix used to indicate the number of atoms of an element in a compound (e.g., di-, tri-, tetra-).

• -ide ending: The suffix added to the second element in a binary molecular compound.

Summary Table: Prefixes and Examples

Prefix	Number	Example Compound	Systematic Name
Mono	1	CO	Carbon monoxide
Di	2	SO2	Sulfur dioxide
Tri	3	N2O3	Dinitrogen trioxide
Tetra	4	CCl4	Carbon tetrachloride
Penta	5	P2O5	Diphosphorus pentoxide

Equations and Formulas

• General formula for a binary molecular compound: $A_xB_y$

• Where $A$ and $B$ are nonmetals, and $x$ and $y$ are the number of atoms indicated by the numerical prefixes.