Names molecular compounds

When two nonmetals combine with each other, the product is most often a binary molecular compound. There is no simple way to deduce the formulas of such compounds. There is, however, a systematic way of naming molecular compounds that differs considerably from that used with ionic compounds. 

Some compounds, namely molecular compounds, contain only nonmetals. Normally the compounds you need to name are binary compounds (containing only two elements). If you have highlighted the metalloids on your periodic table, everything to the right of the metalloids is a nonmetal. The following rules apply to both nonmetals and metalloids. The only nonmetal excluded from these nomenclature rules is hydrogen. 

Naming molecular compounds uses Greek prefixes to indicate the number of... 

In naming molecular compounds, an element s name and its number of atoms are written in Greek, as shown below. 

Formula Common name Molecular compound name... 

This flow chart summarizes how to name molecular compounds when their formulas are known. 

A few other rules are helpful when naming molecular compounds. If only one atom of the first element is listed, the prefix mono is usually omitted. Also, if the vowel combinations 0-0 or a-o appear next to each other in the name, the first of the pair is omitted to simplify pronunciation. Thus, mononitrogen monooxide, NO, becomes nitrogen monoxide. 

Now you are ready to practice naming molecular compounds. Several different molecules can be formed when different numbers of nitrogen and oxygen atoms combine. Look at their formulas in the first colrnnn of Table 5.6, and try to name them without looking at the names listed in the second column. The brown gas pictured is NO2. 

If you answered incorrectly, review Naming Molecular Compounds, page 52. 

TABLE 2.4 Greek Prefixes Used in Naming Molecular Compounds... 

Formula Common Name Molecular Compound Name... 

LiH (lithium hydride) ionic compound BeH2 (beryllium hydride) covalent compound B2H6 (diborane, you aren t expected to know that name) molecular compound CH4 (methane, do you know that one ) molecular compound NH3 (ammonia, you should know that one) molecular compound H2O (water, if you didn t know that one, you should be ashamed) molecular compound HF (hydrogen fluoride) molecular compound. LiH and BeH2 are solids, B2H6, CH4, NH3, and HF are gases, and H2O is a liquid. 

The form for naming molecular compounds is to have the first element preceded by a prefix to indicate the number of atoms present. This is then followed by the second element with its corresponding prefix and -ide placed on the end of the second element. 

Unlike ionic compounds, molecular compounds are composed of individual covalently bonded units, or molecules. Chemists use two nomenclature systems to name binary molecules. The newer system is the Stock system for naming molecular compounds, which requires an understanding of oxidation numbers. This system will be discussed in Section 2. 

The old system of naming molecular compounds is based on the use of prefixes. For example, the molecular compound CCl is named carbon tetrachloride. The prefix tetra- indicates that foiu chloride atoms are present in a single molecule of the compound. The two oxides of carbon, CO and CO2, are named carbon monoxide and carbon rftoxide, respectively. These prefix-based names are often the most widely-recognized names for some molecular compounds. However, either naming system is acceptable, unless specified otherwise. 

Some covalent compounds do not consist of individual molecules. Instead, each atom is joined to aU its neighbors in a covalently bonded, three-dimensional network. There are no distinct units in these compounds, just as there are no such units in ionic compounds. The subscripts in a formula for a covalent-network compound indicate the smallest whole-number ratio of the atoms in the compound. Naming such compounds is similar to naming molecular compounds. Some common examples are given below. 

When naming a molecular compound, the first nonmetal in the formula is named by its element name the second nonmetal is named using the first syllable of its element name, followed by ide. When a subscript indicates two or more atoms of an element, a prefix is shown in front of its name. Table 6.11 lists prefixes used in naming molecular compounds. 

In naming molecular compounds having two elements, prefixes are used to indicate the number of atoms of each nonmetal in a formula. Organic compounds of C and H, such as CH4 and C2H5, use a different system of naming that we will discuss in the next section. A fiowchart for naming the various types of compounds is shown in Figure 6.6. 

---